Zoological Journal of the Linnean Society (2001), 132: 5-0.
With 5 figures
doi: 10.1006/zjls.2OO0.0263, available online a t http;//www.idealibrary.comon
@
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A cladistic analysis of Siboglinidae Caullery, 1914
(Polychaeta, Annelida):formerly the phyla
Pogonophora and Vestimentifera
GREG W. ROUSE
School of Biological Sciences A08, University of Sydney, NSW 2006, Australia
Received August 1999; accepted for publication June 2000
It has been proposed in recent years that the phyla Pogonophora and Vestimentifera are a derived clade of polychaete
annelids. It has also been proposed that if this clade belongs among polychaetes, then the taxon name Pogonophora
is misleading and should revert to a name first formulated for the group, Siboglinidae Caullery, 1914. This
recommendation is adopted in this paper, and a cladistic study using terminals of ‘generic’ rank in the former
Pogonophora (including Vestimentifera) is undertaken. The purpose of this is to assess which taxon names should
now be used for clades within Siboglinidae, and to provide a revised taxonomy, based on phylogenetic principles.
Another major aim is t o assess the position of the vestimentiferan clade within Siboglinidae. The results show that
Vestimentifera is the sister group to Sclerolinum, and this clade is then sister group to Frenulata, i.e. the remaining
Siboglinidae. The results suggest that all taxa within Siboglinidae that are not genera or species are redundant,
except for the following: Siboglinidae is defined as the first polychaete, and all its descendants, to have an gut
occluded by expanded endoderm filled with chemoautotrophic bacteria, as seen in the holotype of Riftia pachyptila
Jones, 1981. Monilifera can be defined based on apomorphy-based system such that it is the first siboglinid, and
all its descendants, to have rings of chaetae (uncini) in the opisthosoma, as seen in the holotype of Sclemlinum
magdulenae Southward, 1972. Vestimentifera can be defined as the first siboglinid and all its descendants to have
a vestimentum as seen in the holotype of Riftia pachyptia. Frenulata is defined as the siboglinid, and all its
descendants, to have a mid-trunk girdle, as seen in the holotype of Siboglinum weberi Caullery, 1914. The taxa of
generic rank are not defined here since their monophyly was not investigated.
0 2001 The Linnean Society of London
ADDITIONAL KEYWORDS: phylogenetic taxonomy - systematics - phylogeny - Monilifera - Frenulata.
INTRODUCTION
with reducing sediments, methane seeps, or with
sunken terrestrial-plant debris.
In his original description, Caullery (1914) noted
that Siboglinum weberi lacked a n obvious digestive
tract, amongst other unusual features, and described
it as having a dorsal nerve cord. He placed S. weberi
in a new family, Siboglinidae, but did not place it
within any other taxon, though he compared it with
deuterostomes such as hemichordates. Uschakov
(1933), apparently unaware of Caullery’s work, described a similar animal, Lamellisabella zachsi Uschakov, 1933from the north-eastern Pacific and placed
it in a new sabellid polychaete subfamily, Lamellisabellinae Uschakov, 1933.Johansson (1937,1939) reassessed the placement of L. zachsi, and decided it
was not a polychaete. He erected a separate taxon
name for it, Pogonophora, with the rank of class, but
did not place it within any other taxon. Subsequent
The varied and complex taxonomic history of Pogonophora and Vestimentifera represents one of the
more fascinating tales in animal systematics. The fact
that they tend to be found in deep-sea sediments
resulted in the first member of this group, Siboglinum
weberi Caullery, 1914, not being described until early
in the 20th century. There are now more than 100
nominal species described, most from abyssal regions,
though exceptionally they are found in depths of less
than 100m (Miura, Tsukahara & Hashimoto, 1997;
Webb, 1964a). Some are large and spectacular members of hydrothermal-vent communities (Jones, 1981a,
b), while others are smaller and found in association
E-mail: [email protected]
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55
0 2001 The Linnean Society of London
56
G. W.ROUSE
workers (e.g. Beklemishev, 1944) then ranked Pogonophora (with reference to Lamellisabella only) as
a phylum among deuterostomes.
Ivanov (1951) compared Siboglinum and Lamellisabella and was the first to recognize that both
must belong t o the same taxon and moved Siboglinum
weberi (and hence Siboglinidae) into Pogonophora. Ivanov (1952) described several new pogonophores and
later published a large monograph on the group (Ivanov, 1960,1963).He regarded pogonophores as having
deuterostome features such as radial cleavage, a dorsal
nerve cord, and a tripartite coelom (formed by enterocoely). Soon after, Webb (1964d) described the hitherto
missing segmented, chaetal-bearing, posterior end
(now called the opisthosoma). After this discovery some
authors felt pogonophores were still deuterostomes
(Ivanov, l970,1975a,b; Johansson, 1968), while others
suggested they were protostomes showing spiral cleavage, a ventral nerve cord, chaetae and metameric
segmentation (Liwanow & Porfirjewa, 1967; N0rrevang, 1970a,b; Southward, 1971b; George & Southward, 1973; van der Land & Nerrevang, 1975).
The resolution of the placement of Pogonophora became more complicated with the description of Lamellibrachia barhami Webb, 1969a from slope depths
off California. Webb (1969a) placed L. barhami in a
new pognophoran taxon, Vestimentifera. Later, closely
related taxa were found at hydrothermal vents, and
these massive worms were described by Jones (1981a,
b), who subsequently placed them in a separate
phylum, Vestimentifera (Jones, 1985a). Jones (1985a)
argued that, in spite of the many similarities between
Vestimentifera and Pogonophora, Vestimentifera was
more closely related to Annelida than to Pogonophora,
thus justifymg their separation. Southward (1988) considered recognition of the phylum Vestimentifera as
untenable, and that vestimentiferans must belong in
the Pogonophora. This view was reinforced by Rouse
& Fauchald (1995) who listed eight synapomorphies
that grouped Pogonophora and Vestimentifera and
showed Jones’ (1985a) reasoning for erecting a phylum
to be flawed. Molecular sequence data (Black et al.,
1997;Kojima et al., 1997;Halanych, Lutz &Vrijenhoek,
1998) also suggest that Pogonophora and Vestimentifera form a monophyletic group.
The idea postulated by Uschakov (1933) and Hartman (1951, 1954) that Pogonophora are polychaetes
was revived by Bartolomaeus (1995), Nielsen (1995)
and Rouse & Fauchald (1995). Rouse & Fauchald
(1997) conducted a series of cladistic analyses of polychaetes and showed that Pogonophora (including Vestimentifera) represents a member of a polychaete clade
called Sabellida. They argued that since the name
Pogonophora was misleading at this level, the name
of the group should revert to that of the first family
group name originally formulated for members of the
group, that of Siboglinidae Caullery, 1914. This name
change was also proposed by McHugh (1997) who,
based on molecular sequence data on a variety of
animals including a vestimentiferan, found that the
latter was nested among polychaetes. It has also been
endorsed in two recent papers on the position of the
group (Halanych et al., 1998; Boore & Brown, 2000).
The suggestion by Rouse & Fauchald (1997) and
McHugh (1997) requires a reassessment of the utility
of the current taxonomy of Pogonophora and Vestimentifera, with both of these names treated, from
this point on, as subsidiary to the name Siboglinidae.
Here cladistic analyses are performed t o assess which
taxon names should now be used for clades within
Siboglinidae. Another major aim is to assess the position of the vestimentiferan clade within Siboglinidae.
A new systematization, based on phylogenetic taxonomy is then provided.
BACKGROUND To CURRENT SYSTEMATICS
Aspects of taxonomy within Siboglinidae ( =Pogonophora and Vestimentifera) are briefly outlined here.
Further details are given in Table 1. Ivanov (1960,
1963) divided the group referred to here as Frenulata
(all Siboglinidae except for Sclemlinum and Vestimentifera, see below) into Thecanephria and
Athecanephria. This was based on the development
of the anterior nephridial system. Unfortunately, it
appears that the only taxa whose nephridia were investigated by Ivanov were members of Siboglinum,
Oligobrachia (Ivanov, 1957) and Lamellisabella, and
there is simply not enough information to assess the
utility of the nephridial system as a character. Nevertheless, Ivanov (1960, 1963) used additional features
such as spermatophore shape to justify his taxonomic
divisions. Within Athecanephria Ivanov (1960, 1963)
placed Oligobrachiidae Ivanov, 1957 with Birstenia
Ivanov, 1952, Nereilinum Ivanov, 1961, Oligobrachia
Ivanov, 1957 (with Crassibrachia Southward, 1978a
and Unibrachium Southward, 1972 added later), and
Siboglinidae with Siboglinum and Siboglinoides Ivanov, 1961. Within Thecanephria he placed Polybrachiidae Ivanov, 1952, with Cyclobrachia Ivanov,
1960, Diplobrachia Ivanov, 1960, Galathealinum Kirkegaard, 1956, Heptabrachia Ivanov, 1952, Polybrachia Ivanov, 1952, Sclemlinum Southward, 1961,
and Zenkevitchianu Ivanov, 1957 [Choanophorus
Bubko, 1965 was added later, though this was then
questioned by (Webb, 1971)l; Lamellisabellidae with
Lamellisabella (and subsequently Siphonobrachia
Nielsen, 1965), and Spirobrachiidae Ivanov, 1952 with
Spimbrachia Ivanov, 1952. This taxonomic system has
remained largely unchanged, with the exception of the
position of Sclemlinum (see below).
When Webb (1969a) described the first vestimentiferan, Lamellibrachia barhami, he assigned
CLADISTICS OF SIBOGLINIDAE (POLYCHAETA)
57
Table 1. Taxonomic arrangements of taxa considered in this paper from when they were considered as Pogonophora
(including Vestimentifera). The taxa Frenulata and Monilifera are as formulated by Ivanov (1991). Athecanephria and
Thecanephria are as formulated by Ivanov (1963)with some subsequent additional taxa. Vestimentifera is as formulated
by Jones (1985a), with some subsequent additional taxa
Higher taxa
Frenulata
Family rank
Generic rank
Siboglinidae
Siboglinum, Siboglinoides
Athecanephria
Oligobranchiidae
Oligobranchia, Nereilinum,
Birstenia, Unibrachium,
Crassi branchia*
Thecanephria
Polybrachiidae
Choanophoms, Cyclobrachia,
Diplobrachia,
Galat hea linu m ,
Heptabrachia, Polybrachia,
Zenkev itchiana
~~
Monilifera
Lamellisabellidae
Lamellisabella,
Siphonobrachia
Spirobrachiidae
S p i n brachia
Sclerolinidae**
Sclemlinum * *
Escarpiidae
Escarpia
Lamellibrachiidae
Lamelli brachia
Ridgeiidae
Ridgeia
Lamellibrachiida
Basibranchia
Tevniida
Vestimentifera
Tevniidae
~~~
Oasisia, Tevnia
~
Arcovestiidae** *
_
Axonobranchia
~~
~
_
_
_
~
Arcovestia
~
?
Alaysiidae
Alaysia
Riftiida
Riftiidae
Riftia
~
* Crussibrachia was originally placed in Polybrachiidae by Southward (1968) and then moved to Oligobrachiidae by
Southward (1978a).
** Monilifera was erected by Ivanov (1991) to accommodate Sclemlinum, which he removed from Frenulata.
*** Arcovestia was associated with Tevniida by Southward & Galkin (1997).
this new taxon to a new class of Pogonophora, Afrenulata, new order, Vestimentifera, and new family,
Lamellibrachiidae. He assigned all previously described pogonophore taxa to a new class Frenulata. The
name Frenulata will be used through the remainder
of this paper to refer to all Siboglinidae, except for
Sclemlinum (see below) and Vestimentifera (Table l),
since this represents the formulation found in some
other recent papers (Ivanov, 1991; Ivanov & Selivanova, 1992), though it should be noted that Southward (1993, 1999) uses the name Perviata for this
assemblage (and includes Sclemlinum). Jones (1981a)
erected two subphyla within Pogonophora, Obturata
containing the class Afrenulata, and Perviata containing Frenulata. Subsequently, a separate phylum
was erected for Obturata by Jones (1985a), which
he called Vestimentifera because this was the most
familiar name. The names Perviata and Obturata are
disregarded here, since they provide no additional
taxonomic information and Perviata (at the time) was
exactly the same taxonomic circumscription as the
older name Frenulata. Jones (1985a) divided Vestimentifera into Axonobranchia and Basibranchia on
the structure of the branchial lamellae (i.e. palpal
crown). In Axonobranchia he placed Riftiidae Jones,
1981a with Riftia Jones, 1981a, and in Basibranchia;
EscarpiidaeJones, 1985a with Escarpia Jones, 1985a,
Lamellibrachiidae with Lamellibmchia, Ridgeiidae
Jones, 1985awith Ridgeia; and TevniidaeJones, 1985a
with Oasisia Jones, 1985a and Tevnia Jones, 1985a.
Subsequently Alaysia spiralis Southward, 1991placed
in Alaysiidae Southward, 1991, and Arcovestia ivanovi
Southward & Galkin, 1997 placed in Arcovestiidae
Southward & Galkin, 1997 were erected. Both these
taxa were placed into Basibranchia.
The taxon Sclemlinurn was originally placed in Polybrachiidae by Southward (1961). Subsequently
Sclerolinurn was placed into SclerolinidaeWebb 1964a,
who regarded this taxon as the most plesiomorphic
pogonophore. Ivanov (1991) and Ivanov & Selivanova
(1992) noted similaritiesbetween Sclerolinurn and Vestimentifera on one hand, and F’renulata on the other
and so decided it should be placed into a new taxon,
Monilifera, with equal rank to Frenulata and Vestimentifera (Table 1).
MATERIAL AND METHODS
TERMINAL, TAXA
The decision made here with regards to terminals was
to use taxa of the ‘generic’rank and assume that they
are monophyletic. The type species of each genus was
not always used to score the characters since in many
cases there was considerable missing information for
the types that could be supplemented by information
from other taxa in the genus. This means that the
scoring for a terminal was in some cases based on
information from a number of different nominal species. Information from types was used where there
was polymorphism for the terminal. Among vestimentiferans this is not particularly problematic,since
six of the eight genera are monotypic anyway. Ridgeia
phaeophiale Jones, 1985a was recently made a synonym of Ridgeia piscesae Jones, 1985a by Southward,
Tunnicliffe & Black (1995), making this genus monotypic, and Larnellibrachia, with five nominal species,
and Escarpia with two nominal species presented no
polymorphisms when it came to coding characters for
this study. Other monotypic siboglinid taxa include
Birstenia, Cyclobrachia, and Zenkevitchiana. Most
other Siboglinidaehave a only a few nominal species,
such as Crassibmhia (2), Diplobrachia (6), Galathealinurn (3), Heptabrachia (7), Lamellisabella (7),
Oligobrachia (8),Nereilinurn (Z), Polybrachia (6), Sclerolinurn (6),Siphonobrachia (Z), and Unibrachiurn (2).
This leaves Siboglinurn as by far the largest taxon,
with 65 nominal species. In general, the taxa were
anatomically relatively uniform, and presented little
difficulty in scoring for the characters used in this
study. There were, however, five instances where polymorphisms were apparent within a terminal. In all of
these cases the condition that is found in the type
species of the genus was med to determine the score.
The five taxa with polymorphisms were Diplobrachia
(number of palps); Nereilinum (the presence of pinnules
and raised ventral glandular areas); Siboglinurn (direction of teeth in uncini); Siphonobrachia (direction
of teeth in uncini); Unibrachiurn (zone of thickened
papillae). Further explanation for each of these problem areas can be found in Appendix 2. In future, the
monophyly of each non-monotypic taxon does need to
be assessed in more restricted analyses. No attempt
was made here to identify apomorphies for the terminals and some taxa are scored as exactly the same
for all characters (i.e. Galathealinurn, Heptabrachia,
and Polybrachia; Larnellisabella and Spimbrachia).
OUTGROUP
In five of the six cladistic analyses on polychaete relationships Rouse & Fauchald (1997) found Siboglinidae (as Frenulata and Vestimentifera)to fall as
the sister group to a clade comprised of Sabellariidae,
Sabellidae, and Serpulidae. In the other analysis Siboglinidae did appear as the sister group t o terebellimorph polychaetes. These analyses differed on in
the number of taxa included, on the character coding
used and on a priori weighting of characters, On the
basis of the overall congruence of results found in
the various analyses in Rouse & Fauchald (1997),
Sabellariidae is chosen as the outgroup for this study,
though further study on the placement of Siboglinidae
is admittedly required. Sabellariids have a pair of
peristomial palps, an anterior pair of large nephridia,
and uncini (Rouse & Fauchald, 1997). This makes
them the most appropriate of the proximate taxa t o
polarize the characters used here since terebellimorphs, sabellids and serpulids have prostomial
palps, and terebellimorph polychaetes also lack the
distinctive pair of large anterior nephridia (Rouse &
Fauchald, 1997).
MORF’HOLOGICAL, FEATURES USED TO DEVELOP
CHARACTERS
The morphology of Siboglinidae is reviewed here with
special reference to those features that provided characters for the cladistic analysis. The characters are
listed and justified Appendix 1and 2 and the matrices
provided in Appendix 3. Siboglinidae have unusual
anatomy and there are several issues concerning their
basic structure that remain t o be resolved, particularly
over the position and delineation of the peristomium
and the first segment. A major factor contributing to
this is that the terminology used t o describe them has
not been that used to described polychaete anatomy.
Studies of larval development (see Bakke, 1990;Southward, 1988) now allow for a reinterpretation of their
structure in terms of polychaete terminology.Note that
CLADISTICS OF SIBOGLINIDAE (POLYCHAETA) 59
the interpretation offered here differs slightly from
that of Rouse & Fauchald (1997).
Pmstomium and peristomium
The structure referred t o as the protosoma by Ivanov
(1994),the tentaculomere by Webb (1969b), ‘segment 1’
by Southward (1988),or the cephalic lobe by Southward
(1993), would appear t o be the prostomium and the
peristomium in most Siboglinidae (Fig. 1A-E). The
small conical prostomium (usually called the cephalic
lobe) is usually clearly distinguishable from the peristomium but in adult vestimentiferans it is either
absent, or completely surrounded by the palps (Fig.
1A-E). There are no eyes or other structures on the
prostomium. The peristomium forms a complete ring,
usually terminated by a clear groove (e.g. labelled s l
fig. B92 in Ivanov, 1963) and bears the palps in most
siboglinids, though, in vestimentiferans the delimitation of the peristomium is uncertain and further
developmental studies are required (Fig. 1A-E). Note
that Rouse & Fauchald (1997) interpreted the region
bearing the frenulum or the vestimentum as being
peristomial, but here it is considered t o be segmental
(though further investigation is required; see below). A
character based on whether the prostomium is clearly
identifiable is used here. The uncertainty about the
peristomium in vestimentiferans precludes the use of
characters associated with this region at this time.
Palps
The palps of Siboglinidae arise behind the larval prototroch (Fig. lB), and hence are peristomial structures
(Rouse & Fauchald, 1997). There can be as few as a
single palp (Siboglinum, Unibrachium), or a pair of
palps (e.g. Crassibrachia, Diplobrachia, Nereilinum,
Sclerolinum). Those taxa with ‘numerous’ palps can
have from 8 or 9 (Cyclobrachia,Heptabrachia) to 1 4 4 0
(e.g. Lamellisabella, Polybrachia, Siphnobrachia,
Zenkeuitchiana), to hundreds (e.g. vestimentiferans,
Galathealinum, Spimbrachia). Sabellariidae (and
many other polychaete taxa) have a pair of peristomial
palps (Rouse & Fauchald, 1997). Dividing the palpal
organization of Siboglinidae into homology hypotheses
is difficult. The adult condition of having a pair of
palps (Crassibrachia, Sclerolinum, S i boglinoides, etc.),
or of having only a single palp (e.g. Siboglinum, Unibrachium) are seen here as clear primary homology
statements (Fig. lB, C). Other taxa are regarded here
as having ‘numerous’ palps (Fig. 1E). The palps of
most siboglinids have pinnules associated with them
(Fig. 1C). The pinnules are comprised of a single cell
in most taxa (Ivanov, 1963), but in vestimentiferans
the pinnules are multicellular (Selivanova, 1989).
Members of Crassibrachia, Choanophorus, Nereilinum
(one of two nominal species), Sclerolinum and some
Siboglinum lack pinnules. The palps can be free from
each other (e.g. Heptabrachia, Polybrachia), or fused
together by the cuticle in frenulates such as Siphnobrachia, Lamellisabella and Spirobrachia, and
in all vestimentiferans. In two vestimentiferan taxa,
Lamellibrachia and Alaysia, the outer palps fuse
(Jones, 1985a) to form lamellar sheaths (Fig. 1E).
Vestimentiferans have a paired structure called the
obturaculum (Fig. 1E). Southward (1988) found that
the obturaculum develops after the larva has a number
of palps, and that it had no counterpart with other
siboglinids. In contrast Ivanov (1989) argued that the
obturaculum is in fact the first pair of palps t o develop,
though they are quickly obscured by the other palps
until a relatively late stage. Jones & Gardiner (1989)
suggested that the first pair of palps (‘larval branchiae’)
disappear, but did not ascertain the origin and development of the obturaculum. Further investigation
seems required on the origin of the obturaculum. The
adult obturaculum can have parasagittal (Oasisia, Riftia, Tevnia) or frontal musculature (Escarpia, Lamellibrachia, Ridgeia). It can also be ornamented with
an axial rod (Escarpia, Oasisia, Riftia, Teunia), and
may have a terminal crust (Escarpia, Tevnia), or saucers (Oasisia, Ridgeia). The obturacular stalk can be
grooved (Alaysia, Amvestia, Lamellibrachia, Oasisia,
Ridgeia, Riftia, Tevnia)) or ridged (Escarpia, Lamellibrachia). The feature used to divide Vestimentifera into Axonobranchia and Basibranchia by
Jones (1985a) is not informative in this analysis, since
only Riftia has the palps fused with the obturaculum
(Southward, 1991).
Segmented region
A vexing question in siboglinid morphology is whether
the bulk of the body can be referred t o as a single
segment or two segments (see Southward, 1971b). In
most siboglinids the region immediately behind the
head, termed the mesosoma by Ivanov (1994), the
frenulomere by Webb (1969b), and the forepart by
Southward (1993), bears a cuticular structure called
the frenulum (Fig. 1A-D). In vestimentiferans the
equivalent region is called the vestimental region (Fig.
1E) and has no frenulum (Gardiner & Jones, 1993).
The next body region is generally referred t o as the
trunk or metasoma (Ivanov, 1994; Southward, 1988).
Southward (1980, 1988) regarded the trunk plus the
area bearing the vestimentum, or frenulum, as a single
segment. However, Nerrevang (1970a) in describing
the early development of Siboglinum clearly described
the development of the diaphragm and it does suggest
that the forepart (or vestimental region) and trunk are
two (or more) segments, not one. This issue appears
t o require further investigation, and is not of major
relevance here.
60 G. W.ROUSE
Figure 1. Features of Siboglinidae used to generate characters. A, generalized siboglinid. The prostomium and
peristomium (bearing the palps) comprise what was formerly regarded as the protosoma. The next region (dark stipple)
that has the frenulum, and terminates a t the diaphragm, was formerly regarded as the mesosoma. This area may be
part of the first segment. The trunk (light stipple) is either the bulk of the first segment or comprises the second
segment. The trunk can have an anterior metameric papillate region dorsally, an area of thickened dorsal papillae
and posterior rows or lines of dorsal papillae. There may also be posterior ventral raised glandular areas. The midregion of the trunk has a girdle of uncini. The body terminates with the multi-segmented opisthosoma bearing peglike chaetae or uncini (redrawn from Southward, 1975b). B, lateral view of a Siboglinum larva. The palp develops
behind the ciliary band known as the prototroch, thus making it a peristomial structure. The limit of the peristomium
is indicated based on comparison with adult morphology. The first segment may be the region that has the frenulum
and terminates at the diaphragm, or this area may be only part of the first segment. The trunk then is either the bulk
of the first segment or the second segment (redrawn from Southward, 1975b). C, lateral view of the anterior end of
CLADISTICS OF SIBOGLINIDAE (POLYCHAETA)
The frenulum (or bridle) is a pair of cuticular crests
that run obliquely around the forepart (Fig. 1A-D).
Developmental evidence from Nereilinum suggests the
frenulum develops from cuticular plaques (Ivanov,
1994). Similar plaques are scattered on the vestimental
region of vestimentiferans and just behind the palps
in Sclemlinum. The condition of scattered plaques in
the vestimental region is scored as a state in the
character ‘Frenulum’ in the Multistate analysis, but a
frenulum proper is not considered present in Vestimentifera. However, in members of Sclemlinum there
are two rows of plaques that positionally would appear
justifiably to be called a frenulum (Ivanov, 1994). The
vestimentum of vestimentiferans is a pair of longitudinal flaps along the dorsal part of the vestimental
region that overlap mid-dorsally forming a longitudinal
space over the segment (Fig. 1E). The vestimentum
also projects forward to form a collar around the base
of the palpal crown. In most siboglinids the region
bearing the frenulum terminates a t the muscular diaphragm with a clear external groove (Fig. 1A-C). In
Sclemlinum and vestimentiferans there is no clear
demarcation (Fig. lD, E). The pair of excretory organs
are for the most part in the frenular or vestimental
region, and usually have separate openings on each
side of the peristomium, or a t the base of the obturaculum in vestimentiferans. The vestimentiferans
61
Lamellibrachia and Escarpia are unusual in that there
is a single mid-dorsal exit for the nephridia (Jones,
1988). A single pore for the pair of anterior nephridia
is found in sabellids and serpulid polychaetes, though
in Sabellariidae there are separate openings for each
of the two nephridia (Orrhage, 1980). Although Ivanov
(1960, 1963) used nephridial structure as the basis for
his taxonomy there is too little information across the
group to use his criterion as a character.
The next body region, the trunk (possibly the second
segment), comprises most of the body in siboglinids
(Fig. 1A). The anterior region (usually called the preannular region) often has two rows of papillae (Fig.
lA, C). This ‘metameric’ region is absent in groups
such as Nereilinum and Sclemlinum which have longitudinal ridges of pyriform glands. In vestimentiferans there are scattered pyriform glands in
this area (Gardiner & Jones, 1993; Webb, 1969a).
Behind the anterior trunk section are more scattered
papillae followed, in some taxa (e.g. Oligobrachia, Heptabrachia), by a region of enlarged papillae and a
ventral ciliated region (Fig. lA, F). In some cases (e.g.
Siboglinoides, Cyclobrachia) the papillae of this region
of the trunk in front of the uncini are simply scattered.
A girdle of uncini in the mid-region of the trunk is
present in all siboglinids (Fig. lA, B, H), except for
Sclemlinum and vestimentiferans. The uncini typically
~
Siboglinum pinnulatum Ivanov, 1960 showing the prostomium, peristomium with a single palp (bearing pinnules),
and frenulum. Metameric papillae begin immediately behind the diaphragm (redrawn from Ivanov, 1963). D, lateral
view of Sclemlinum sibogae showing a pair of palps and a frenulum. The prostomium is distinguishable as a projecting
ventral lobe but the peristomium has yet to be demarcated. There is no clear diaphragm between the region bearing
the frenulum and the trunk (redrawn from Southward, 1961). E, dorsal view of anterior end of Lamellibrachia satsuma,
showing the obturaculum, ‘numerous’ palps that are fused into outer lamellar sheaths and the vestimentum. The
vestimentum region is supposed to be homologous with the region bearing the frenulum in other siboglinids (redrawn
from Miura et al., 1997). F, dorsal view of the region of thickened papillae of Polybrachia canadensis (Ivanov, 1962)
(redrawn from Ivanov, 1963). G, dorsal view of girdle with two rows of uncini of Siboglinum caulleryi Ivanov, 1951
(redrawn from Ivanov, 1963).H, lateral view of girdle uncinus of Polybrachia annulata Ivanov, 1952 showing teeth
facing in opposite directions (redrawn from Ivanov, 1963). I, peg-like chaeta from opisthosoma of Siboglinum poseidoni
(drawn from micrographs in Flugel & Callsen-Cencic,1992; Southward, 1993).J, dorsal view of Polybrachia canadensis
showing girdle with two rows of uncini and posterior trunk papillae in rows (redrawn from Ivanov, 1963). K, lateral
view of posterior trunk of Nereilinum murmanicum Ivanov, 1961, showing regularly spaced dorsal papillae and ventral
glandular shields (redrawn from Ivanov, 1963).L, opisthosoma of Polybrachia canadensis showing a clear demarcation
between the trunk and opisthosoma and the peg-like chaetae in each opisthosomal segment (redrawn from Southward,
1969). M, opisthosoma of Sclemlinum magdalenae Southward, 1972 showing rows of uncini in each segment. There is
no clear separation between the trunk and the opisthosoma and the first row of uncini correspond t o the girdle chaetae
of most siboglinids (redrawn from Southward, 1972). N, opisthosoma of Arcovestia ivanoui showing rows of uncini on
each segment (redrawn from Southward & Galkin, 1997). 0, narrow spindle-like spermatophore of Siboglinum fedetoui
Ivanov, 1957 with elongate filament (redrawn from Ivanov, 1963). P, broad, flattened leaf-like spermatophore of
Lamellisabella johanssoni Ivanov, 1957, with elongate filament (redrawn from Ivanov, 1963). Q, rigid tube with funnels
as found in Lamellisabella, Spirobrachia and vestimentiferans (redrawn from Webb, 1971). R, membranous and
collapsed anterior end of tube as seen in many siboglinids (redrawn from Webb, 1971).Abbreviations: cb = ciliary band,
d = diaphragm groove, f = frenulum, g = mid-trunk girdle of uncini, mp = metameric papillae, o = obturaculum, op =
opisthosoma, outer sheath lamellae, p = prostomium, pa = palp, pe =peristomium, pi =pinnules, pg = peg-like chaetae,
pp =line or row of posterior trunk papillae, pr = prototroch, ru =rows of uncini, s = septum, t = trunk, tp =thickened
zone of papillae, tu = row of uncini on posterior trunk, v = vestimentum, vg =ventral glandular shields.
62
G. W. ROUSE
lie as two pairs of semicircular bands on epidermal
ridges (Fig. 1G). Behind the uncini there may be a
transverse row of dorsal papillae (e.g. Larnellisabellu),
or the papillae may be single at any one point and so
form a longitudinal row (e.g. Oligobrachia, Nereilinum). There may also be ventral glandular shields
opposite the papillae (e.g. Siboglinurn, Nereilinum)
(Fig. lA, J, K). In Sclemlinurn and vestimentiferans
there are only scattered papillae along the length of
the trunk. The trunk in most siboglinids terminates
with an obvious septum and external groove (Fig.
lA, L). The remainder of the body is a short multisegmented region called the opisthosoma, or telosoma
(Fig. lA, B, L N ) . Southward (1972) and Ivanov (1994)
have noted that the opisthosoma of Sclemlinurn and
vestimentiferans (e.g. Ridgeia, Riftia) has no clear
demarcation (Fig. lM, N). It appears that chaetae in
front of the first opisthosomal septum in these groups
are at the end of the trunk, and so correspond to the
girdle of uncini on the trunk of other siboglinids. The
anterior segments of the opisthosoma have chaetae
that, in Sclemlinurn and vestimentiferans, are uncini
in rows (Fig. lM, N). In other siboglinids there are 4
‘peg-like’chaetae in most segments (Fig. lB, I, L). The
uncini of nearly all siboglinids have two groups of teeth
that face in opposite directions (Fig. lH), a feature not
seen in polychaete uncini. It should be noted that
Cyclobrachia auriculata Ivanov, 1960 and some members of Diplobrachia, Siboglinum and Siphnobrachia
do have uncini where all teeth face in the same direction (Ivanov, 1963; Nielsen, 1965).
Reproduction
Males of all siboglinids, except Sclemlinurn and vestimentiferans, produce masses of broad, leaf-shaped
or narrow, spindle-shaped spermatophores that are
spawned into the water (Fig. 10, P). Some taxa such
as Siphonobrachia and Zenkvitchiana have spermatophores which seem to fall between the two states
defined by Ivanov (1963). For Sclemlinurn there were
initial reports of spermatophores but these were later
discounted. It would appear that in Sclemlinurn and
Vestimentifera sperm are spawned freely, or in unenclosed bundles (spermatozeugmata) (Southward,
1971b; Southward & Coates, 1989), though the spawning method is unknown for many in the latter taxon.
Gut
Nutritional requirements for siboglinids are met
through their symbiotic relationship with chemoautotrophic bacteria that occupy cells (baderiocytes)
in the expanded endoderm (trophosome). Adult siboglinids have no obvious mouth and the gut lumen
is nearly completely occluded by the endoderm, though
a small lumen does appear to be present in those that
have been studied (e.g. Southward, 1982). According
to Southward (1982), this was previously referred to
as the medial coelomic cavity by Ivanov (1963). A
transitory opening to the gut, either posteriorly or
anteriorly, has been shown in Siboglinum poseidoni
Flugel & Langhof 1983 by Callsen-Cencic & Flugel
(1995) and in Ridgeia spp. (Jones & Gardiner, 1988;
Southward, 1988), and this appears t o be the pathway
whereby bacteria are acquired to occupy the trophosome.
mbes
The tubes of siboglinids are distinctive, and their structure and variability was reviewed by Webb (1971),
who also commented on their systematic value. Webb’s
(1971) conclusion that there are two fundamental tube
types in siboglinids is used here for character construction (Fig. lQ, R). He found that tubes could have a
collapsibleanterior end (e.g. Oligobrachia,Nereilinum,
Sclemlinurn, Siboglinoides, Siboglinum), or it could be
rigid, often resembling a series of funnels stacked on
each other ( C h a n o p h r u s , Lamellibrachia, Spimbrachia, Larnellisabella). All vestimentiferans are
considered here to have these rigid tubes. Webb (1971)
found that some taxa that had been included in Polybrachia and Galuthealinum by Ivanov (1963) probably
should be excluded from these taxa on the basis of
their tube morphology, but did not resolve where they
should actually be transferred to. These nominal species were not considered when coding their respective
terminals for this study. Like many polychaetes, the
tubes of Sclemlinum and Vestimentifera are attached
to hard substrates while other siboglinids are unique
in having tubes that are buried in sediment for at least
a third of their length (Webb, 1971).
MORPHOLOGICAL FEATURES NOT USED
There are a number of features that have been used
in siboglinid descriptions that are not implemented
here. As mentioned above the organizationof nephridia
was used by Ivanov (1957) t o erect Thecanephria and
Athecanephria. However, he only discussed descriptions for members of Siboglinum, Oligobrachia,
and Larnellisabellu, and seems to have relied on other
features such as spermatophore structure t o place
taxa into Thecanephria or Athecanephria. Southward
(1993) has added further data on Siphnobrachia and
showed that the distinctions between the Thecanephria and Athecanephria conditions are not as clear
as Ivanov (1963) suggested. The lack of any published
data for most of the taxa under investigation here
precludes the use of any nephridial characters beyond
the one involving the number of excretory openings.
Most Siboglinidae would appear to have cuticular
plaques on various regions of the body. Aspects of their
CLADISTICS OF SIBOGLINIDAE (POLYCHAETA)
shape and distribution on papillae have been used
as a character t o distinguish among nominal species
(Ivanov, 1963). However, there has been no systematic
documentation of these structures across the group. It
appears that, at the hierarchical level used here, no
purpose would be served by including this data owing
t o difficulties in establishing primary homology hypotheses and polymorphisms. This problem is discussed by Nielsen (1965). The papillae that are found
behind the girdle of chaetae in many siboglinids are
characterized as being in repeated rows in many taxa
and as a series of individual papillae forming a line in
others (Oligobrachia, Nereilinum, Siboglinoides, Siboglinum). However, as discussed by Nielsen (1965)
there is considerable polymorphism of these features
and so a general character based on the presence of
orderly rows, or a line, of papillae was used.
63
using Sabellariidae as outgroup. Unknown character
states were coded with a ‘?. Zero-lengthbranches were
collapsed and MULF’AFtS was activated. Tree searches
were performed using the random addition search
command with 100 replicates. Analysis of character
optimizations were performed using PAUP and MacClade 3.07 (Maddison & Maddison, 1997).Where there
are various possible most-parsimonious transformations for a given character the ACCTRAN transformation is used here, where possible, since this
maintains the primary homology hypotheses t o a large
extent (de Rnna, 1991). For Multistate characters
there is often no way that one can choose between
alternative optimizations and they are all discussed.
The matrices are shown in Appendix 3 and can also
be found, along with the resulting tree files from the
following
addresses:
TreeBASE
(httpjherbaria.harvard.edu/treebasa, and the author’s website
(http j//www.bio.usyd.edu.au/papers/gregrf)
CLADISTIC ANALYSIS
Problems with character coding for cladistic analyses
have been addressed by several authors (e.g. Pleijel,
1995; Wilkinson, 1995b). Here the same strategy used
by Rouse & Fauchald (1997) is implemented in that
both Absenmesent coding (Pleijel, 1995) and Multistate coding is used. For the Absenmesent matrix
all 44 characters were treated either as of equal weight
(as the A/Pe analysis) even if they were linked (e.g.
characters based on the substructures of the obturaculum are linked to the presence of the obturaculum in the first place). Weighting to control for
such linkage was applied, as in Rouse & Fauchald
(1997), for the characters with linkage (as the A/pw
analysis). This meant that all arguably independent
characters were given a weight of 1. Subsidiary characters were given a weight of 0.5. These characters
were those involving substructures of the multiple
palps (‘lamellar sheaths’ ‘fused palps’), obturaculum
(‘frontal’or ‘parasagittal’obturacular musculature, ‘axial rod, ‘groovedor ‘ridged obturacular stalk) pinnules
(‘single-celledor ‘multicellular’),and the types of spermatophores (‘leaf‘or ‘spindle’).Two characters (‘crust’
and ‘saucers’)that were subordinate t o the presence
of an axial rod in the obturaculum were given a weight
of 0.25. For the Multistate analysis, coding various
features that are arguably ‘homologous’ as states
within one character (e.g. spermatophores can be
‘broad o r ‘narrow’) was used. For taxa where such
characters are inapplicable, a ‘-’ is used that is treated
as a missing state by the program, with various inherent problems (Nixon & Davis, 1991; Platnick, Griswold & Coddington, 1991; Pleijel, 1995; Wilkinson,
1995a).
Cladistic analyses were performed using PAUP* version 4.0b4a (Swofford, 2000). Trees were rooted, and
hence characters polarized (Nixon & Carpenter, 1993),
RESULTS
The three separate ways of treating the data gave
results that had the same overall implications in terms
of the revised taxonomy adopted here, but there were
some minor differences that will be outlined. The A/
Pe analysis resulted in 240 most parsimonious trees
of length 79 (consistency index CI =0.56; retention
index RI = 0.86; rescaled consistency index RC = 0.48).
The strict consensus tree is shown in Figure 2A. The
A/pw analysis resulted in 1104 shortest trees of length
66.75 (CI = 0.55; RI = 0.86; RC = 0.48). These 1104trees
are not congruent with the shortest trees from the A/
Pe analysis and represent, when reweighted according
the A/Pe system, 684 trees that correspond to trees of
length 80, and 420 trees that are of length 81, i.e. one
or two steps longer than the A/Pe analysis results. The
strict consensus tree of the A/F’w trees is shown in
Figure 2B. The Multistate analysis found 6112 most
parsimonious trees of length 58 steps (CI = 0.70; RI =
0.89; RC = 0.63). When the length of these trees is
measured using the A/Pe matrix they range between
79 and 86 steps, with the 112 trees of length 79
representing a subset of the 240 shortest trees found
in the A/pe analysis. The strict consensus of the Multistate shortest trees is very similar t o that of the A/
Pe analysis and is shown in Figure 2C.
In the all three analyses there were several consistent clades:
1. Vestimentiferans (in the traditional usage, Table
1) formed a clade that was the sister group to
Sclemlinum and this clade is the sister group t o
the remaining ingroup taxa.
2. The remaining siboglinids, (Frenulata in Table l),
64
G. W.ROUSE
I
T1
Figure 2. Consensus trees from the three parsimony analyses. In all three analyses Sclerolinum was always the sister
group to the vestimentiferan clade. The relationships among the other siboglinids (Frenulata) varied in each analysis
and none of them matched the currently accepted groupings of the genera. A, strict consensus of 240 shortest trees
(length 79) generated from the m e matrix. B, strict consensus trees of 1104 shortest trees (length 66.75) found using
the A/Pw matrix. C , strict consensus trees of 6112 shortest trees (length 58) found with the Multistate matrix.
CLADISTICS OF SIBOGLINIDAE (POLYCHAETA)
formed a clade, and of these Nereilinum and Crassibrachia always formed a grade with respect t o the
remaining taxa.
3. Cyclobrachia, Lamellisabella, Siphonobrachia and
Spimbrachia formed a clade.
In A/p coding, under both weighting schemes, Lamellibrachia and Escarpia form a clade in all trees that
was the sister group t o the remaining vestimentiferans.
Within this clade the relationships varied among the
trees, but Ridgeia and Oasisia were always sister
groups, and formed a clade with Tevnia (Fig. 2A, B).
In the A/Pw analysis there was considerable topological
variation in relationships within Frenulata, which was
largely caused by the variable placement of Diplobrachia. However, Zenkevitchiana was always the
sister group t o the clade formed by Cyclobrachia, Lamellisabella, Siphonobrachia and Spimbrachia (Fig.
2B).
In Multistate coding there was considerable variability in the topologies for the relationships among
vestimentiferans (Fig. 2C). However, the relationships
among Frenulata in the Multistate analysis were basically the same as found by the @e analysis in that:
Choanophorus was always the sister group to the
remaining Frenulata.
Diplobrachia, Galathealinum, Heptabrachia and
Polybrachia always formed a clade.
This clade was always sister group t o the Cyclobrachia, Lamellisabella, Siphonobrachia and
Spimbrachia clade.
Zenkevitchiana and Siboglinoides always formed
a grade with respect to the clade described in 3.
TRANSFORMATIONS
The tree used t o show transformations for the @ and
Multistate matrices is one of the 240 shortest trees
(length=79) found in the @e analysis that is also
one of the 6112 trees found in the Multistate analysis.
The results of the A/pw analysis are the same as the
@e and Multistate analyses with respect to the major
clades. The transformations that supported the major
clades in all trees in each of the three analyses are
outlined here (Figs 3, 4) and summarized in Table 2.
A / P analyses
In both A/P analyses the monophyly of Siboglinidae
was supported by the presence of a frenulum (19)
(under ACCTRAN, and this means this feature was
lost in vestimentiferans), a trunk (22), an opisthosoma
(32), uncini with groups of teeth facing in opposite
directions (34) (subsequently lost in Cyclobmhia and
Siphonobrachia), a gut lumen that is largely occluded
(41), and a tube with a collapsible anterior end (43)
(under ACCTRAN, and this means this feature was
65
lost in vestimentiferans and some other siboglinids).
The clade formed by Sclemlinum and vestimentiferans
was supported by the presence of uncini at the posterior
end of the trunk (26), scattered trunk papillae (28),
uncini only in all posterior segments (33), rings of
chaetae in posterior segments (36) and, under an
ACCTRAN transformation that assigned spermatozeugmata to Sclemlinum, the presence of spermatozeugmata (40). The monophyly of Frenulata was
indicated by the presence of a number of features: a
clear diaphragm groove at the beginning of the trunk
(21), a mid-trunk girdle of uncini (25), a zone of
thickened papillae on the trunk (27) (subsequently
lost in some taxa), ventral glandular shields on the
posterior trunk (29) (subsequently lost and regained
in one clade), dorsal papillae in a line or rows on the
posterior trunk (30), a marked opisthosomal diaphragm (31), ‘peg’-like chaetae (35), spermatophores
(37), that are narrow (39) (subsequently lost in one
clade), and a tube that lies buried unattached in the
sediment (44).
The monophyly of the vestimentiferan clade was
indicated by the gain of an indistinct prostomium (l),
‘numerous’palps (4), pinnules (5), that are multi-celled
(7), a cuticle that fuses the palps (at least in part) (8),
an obturaculum (lo), a vestimentum (18), and the
presence of a rigid tube (42). It was also supported by
the loss of a pair of palps (3) and loss of a frenulum (19)
(under ACCTRAN). The clade formed by Cyclobrachia,
Lamellisabella, Siphonobrachia and Spimbrachia was
supported in all @analyses trees by the (homoplastic)
presence of fused palps (8). The sister group of this
clade (in the @e analysis), comprised of Diplobrachia,
Galathealinum, Heptabrachia and Polybrachia was
supported by the (homoplastic) presence of a zone of
thickened papillae (27), and the loss of scattered papillae (28). The sister group relationship of these two
clades was supported by the loss of narrow spermatophores (39), and the presence of broad spermatophores (38). With the exception of vestimentiferans,
all taxa with ‘numerous’palps (4) formed a clade but
this (and the loss of a pair of palps, 3) was the only
feature supporting its monophyly. The other relationships shown in Figure 3 were also only generally
supported by one or a few character transformations.
The situation was similar in the Multistate analysis
and the transformations for the same tree as for the
@e analysis is shown in Figure 4.
Multistate analyses
Most of the transformations occur in the basal part
of the Multistate analysis trees and there was little
support for clades at more restrictive levels (Fig. 4).
When there are multiple equally parsimonious transformations for a character, the nature of unordered
66
G.W. ROUSE
'IBble 2. List of unambiguous apomorphies (i.e. those that occur in each most parsimonious transformation) found in
both the A/P and Multistate coding analyses supporting the four major clades named in this study. *ACCl"
transformation (see text for details)
Multistate analysis
Unambiguous apomorphies
A/P analyses
Unambiguous apomorphies
Presence of: Frenulum* (19); Trunk (22);
Opisthosoma (32); Uncini opposed teeth (34);
Occluded gut (41); Collapsible tube* (43)
Presence of: Frenulum (12:l); Trunk (15:l);
Ridges with pyriform glands on the anterior
trunk (161); Opisthosoma (21:l); Uncini with
opposed teeth (25:l); Occluded gut (282);
Collapsible tube (291)
Monilifera
Presence of: Uncini at posterior of trunk (26);
Scattered trunk papillae (28); Uncini only in all
posterior segments (33); Rings of opisthosomal
chaetae (36);Spermatozeugmata*(40)
Presence of: Rings of opisthosomal chaetae (24:l);
Spermatozeugmata*(26:2). Also various
ambiguous transformations.
Frenulata
Presence of: Anterior Diaphragm (21); Midtrunk with chaetal girdle (25); Zone of thick
papillae (27); Ventral glandular shields (29);
Dorsal papillae (lines or rows) (30);
Opisthosomal diaphragm (31); 'Peg' chaetae
(35); Spermatophores(37); that are Narrow
(39); Buried tube (44)
Presence of: Anterior diaphragm (14:l); Ventral
glandular shields (191); Buried tube (301). Also
various ambiguous transformations.
Vestimentifera
Presence of: Indistinct prostomium (1);
'Numerous' palps (4);Pinnules (5), that are
multicelled (7); Fused palps (8); Obturaculum
(10); Vestimentum (18); Rigid tube (42). Loss of:
Paired palps (2); Frenulum* (19)
Presence of: Indistinct prostomium (1:l);
'Numerous' palps (2:2); Multicelled pinnules (3:
1);Fused palps (4:l); Obturaculum (6:l);
Vestimentum (1l:l);Frenulum area has
scattered plaques only (12:2); Anterior trunk
with metameric papillae (16:3); Rigid tube (29:2).
Siboglinidae
( = Pogonophora)
multistate characters means it can be impossible to
decide along which branch transformations between
states for that particular character may occur. For
example, Multistate character 17 (Segment 1 or 2
(Trunk) with girdle of uncini) has three states: 0.
Absent, 1. Present middle, 1. Present posteriorly. Allowing for further outgroup considerations, in all trees
there is a transformation to either state 1 or 2 below
the ingroup node (i.e. Siboglinidae) or states 1 and 2
evolved independently from the absent state. We can
discount the latter possibility on the basis that the
two conditions of the girdle should be accepted as
homologous in line with principles outlined by de Rnna
(1991), and so should not be seen to have evolved
independently. But there is no justifiable way to choose
between the hypothesis that the girdle of uncini was
initially (i.e. plesiomorphic for Siboglinidae) in the
mid-trunk (state 1) and then transformed to the posterior trunk (state 2) along the branch leading to the
node joining Sclemlinum with vestimentiferans, or
vice-versa. The approach taken here is therefore to
indicate on Figure 4 that a transformation either has
taken place below the node from which the branch
originated, or will occur along that branch. This is
indicated by placing the character state in brackets
on the branch where the node above (or terminal)
unambiguously has that state. Most of these ambiguous transformations occur in the basal part of the
tree. This means that there a number of transformations that support the monophyly of Siboglinidae
that are not shown, or that various apomorphies for
the two major subclades of Siboglinidae are not shown.
The unambiguous transformations for Siboglinidae
were the presence of the following features: a frenulum
(12, state l),a trunk (15, state l), ridges with pyriform
glands on the anterior trunk (16, state l), a n opisthosoma (21, state l),uncini with teeth facing the
opposite direction (25, state l), an occluded gut (28,
state l), a collapsible tube (29, state 1). The unambiguous transformations for the Sclemlinum plus
vestimentiferan clade were the presence of rings of
chaetae in the posterior segments (24, state l), and
the presence of spermatozeugmata (26, state 2) (under
an ACCTRAN transformation that assigned spermatozeugmata to Sclemlinum). There were a number of
other ambiguous transformations that could serve as
synapomorphies for this clade, namely the presence of
a scattered papillae in the anterior trunk (17, state 2),
a girdle of uncini at the posterior end of the trunk (18,
state 2), scattered papillae on the posterior trunk (20,
CLADISTICS OF SIBOGLINIDAE (FQLYCHAETA)
67
I
I1 ACC
6
'fg
4 ACC
T
31
35
37
39
43 ACC
Figure 3. Character transformation on one of the 240 shortest trees from that A/pe analysis that also matched one
of the shortest trees from the Multistate character analysis. Slashes on branches indicate transformation of the
character below the node. Character details are in the text, and listed in Appendix 1. Character numbers in plain text
indicate a transformation from absent to present and that there is no homoplasy for that character. Underlined
characters show homoplasy in the form of convergence and outlined characters represent reversals to the absent state.
Characters with the letters ACC after them means that the ACCTRAN transformation requires the state change along
that branch, but that other possible transformations (i.e. for less inclusive clades) are equally parsimonious. The
clades Siboglinidae, Monilifera (=Vestimentifera plus Sckmlinurn) and Frenulata are all supported by a number of
synapomorphies.
68
G. W. ROUSE
6
*l
11-1
12-2
16-3
29 -2
fz-2
tl6-2
I
--- .16+1
30-1
12-1
15+1
21-1
29-1
Figure 4. Character transformations on one of the shortest trees from that Multistate analysis that is the same as
one of the trees resulting from the A/Pe analysis. Slashes on branches indicate transformation of the character below
the node 'above'. Character details are in the text and listed in Appendin 1.Arrows after a character number indicate
a transformation to the state listed. Brackets around a character state indicate that it must have transformed to that
state below the next node but may also have transformed to this state below a preceding node. Character states in
plain text indicate there is no homoplasy for that state. Underlined characters show homoplasy in the form of
convergence, and outlined characters represent reversals to the absent state. The * next to a transformation for
character 26 (Sperm packaging) under ACCTRAN assigns Sckmlinum with spermatozeugmata (though it has yet t o
be observed), thus making it a synapomorphy grouping it with vestimentiferans. All taxa with no spermatophores
were assigned with ? for character 27 (Spermatophore type) and these were all assigned state 0 (Narrow, spindleshaped). I have indicated the transformation to this state 27-0 where it is actually logical to do so, along the branch
that supports the clade Frenulata. The clades Siboglinidae, Monilifera, and Frenulata (all defined as taxa in the
Discussion) are each supported by a number of synapomorphies.
CLADISTICS OF SIBOGLINIDAE (POLYCHAETA)
state 2), no clear separation between the trunk and
opisthosoma (22, state O), and that all chaetae in
posterior segments are uncini (23, state 1).
The monophyly of Frenulata was unambiguously
supported by the presence of a clearly grooved diaphragm a t the beginning of the trunk (14,state l),the
presence of ventral glandular shields in the posterior
trunk (19, state l), and the presence of a tube that
lies freely in the sediment (30, state 1). The ambiguous
transformations that could serve as synapomorphies
for this clade were the presence of a zone of thickened
papillae (17, state l),the presence of a girdle of uncini
in the mid-trunk (18, state l), the presence of a line
or rows of papillae on the posterior trunk (20, state
l), a clear separation between the trunk and opisthosoma (22, state l), that all chaetae in posterior
segments are ‘peg-like’(23, state 2), and the presence
of spermatophores (26, state 1). The character based
on spermatophore shape (27) can only logically be
applied to those taxa with spermatophores i.e. Frenulata. However, given the topology of the shortest
trees, and since taxa without spermatophores were
scored with ‘-’ for this character, all optimizations
applied give these taxa the state 0 (‘Spindle-shaped
spermatophores’). In fact, the only place that the state
0 should be applied is below the node for Frenulata.
While there is a most parsimonious transformation for
spermatophores to be plesiomorphic for Siboglinidae
as a whole, it is not appropriate for a possible transformation to the presence of spindle-shaped spermatophores below this node. To do this would mean
that the vestimentiferan plus Sclemlinum clade would,
inappropriately, have to be considered as having this
state. The only other clade that is consistently supported by more than one synapomorphy is Vestimentifera, where there are nine (Fig. 4;Table 2).
DISCUSSION
There have been two previous explicit hypotheses of
the phylogeny of Siboglinidae, and these are shown in
Figure 5. Both of these hypotheses were developed
before the description of a number of taxa, including all
vestimentiferans (Ivanov, 1963; Webb, 1964b). Ivanov
(1963) argued that the plesiomorphic siboglinid had
six palps, and that this had been elaborated into a
complex array of palps in groups such as Spimbrachia,
reduced to pair of palps (for Diplobrachia), or to a
single palp as in Siboglinum. Ivanov (1963) suggested
that Heptabrachia and Oligobrachia retained many
plesiomorphic siboglinid features, and depicted this by
drawing a thicker line to these terminals from the
hypothetical ancestor (Fig. 5A). Webb (1964b) incorporated information about Sclemlinum, which had
not been included in Ivanov’s discussion, and argued
that the plesiomorphic condition for Siboglinidae was
69
A
Hyp. Anc.
Figure 5. Previous hypotheses about the evolution of
Siboglinidae. A, tree outlining ideas of Ivanov (1963).
Taxa such as Choanophoms, Nereilinum, Siboglinoides,
Siphombrachia and vestimentiferans were unknown, or
not considered, when this tree was published. Ivanov
(1963, 1970) argued that the hypothetical ancestor had
six palps and that this condition had been maintained in
members of Heptabrachia and Oligobrachia (he depicted
this by drawing a thicker line to these terminals from the
hypothetical ancestor)with other taxa showingreductions
or elaborations from this number. B, tree outlining ideas
of Webb (196413). Taxa such as Choanophorus, Siphonobrachia and vestimentiferans were unknown when
this tree was published. Webb (196413) argued that the
hypothetical ancestor had two palps and that Sclemlinum
closely resembled this hypothetical ancestor.
70
G . W. ROUSE
t o have a pair of palps. Webb suggested that Sclem-
linum represented the most plesiomorphic group of
Siboglinidae (Fig. 5B), but in other respects (allowing
for other added taxa) his phylogenetic hypothesis was
similar to that of Ivanov (1963). Ivanov (1970) reiterated his support for his earlier, (Ivanov, 1963),
hypothesis and rejected Webb’s (196415) suggestion regarding Sclemlinurn as plesiomorphic.
The results shown here do not lend support to the
hypotheses of Webb (1964b) or Ivanov (1963, 1970).
However, the differences in the taxa that were available for consideration between then and now do have
t o be taken into account. Allowing for the fact that
vestimentiferans were unknown when Webb (1964b)
developed his hypothesis, excluding them from the
results obtained here places Sclemlinurn as sister
group to the remaining Siboglinidae. However, the
remaining details of his proposed phylogeny largely
followed Ivanov’s (1963). If the other taxa that were
not included in either Webb’s or Ivanov’s proposed
phylogenies are also excluded from the topologies proposed here, then the results still show that their hypotheses are not parsimonious explanations of the
data. To demonstrate this further I performed analyses
with the A/P and Multistate matrices on the taxa only
included in Ivanov’s (1963) tree. Characters that were
uninformative for this restricted taxon set were excluded (i.e. characters 1-3, 5-7, 9-26, 30-37, 40, 41,
44, or Multistate characters 1-3, 5-16, 18, 20-26, 28,
30). This resulted in 13 shortest trees of length 12 for
the A/pe trees, 8 shortest trees of length 9.5 for the A/
F’w trees and 12 shortest trees of length 6 for the
Multistate matrix. These results all provided trees
that were congruent, given the deleted taxa, with the
results of the complete taxa analyses performed here.
In contrast, when applying Ivanov’s (1963) topology to
the data matrices, the lengths were 20 for the A/Pe
matrix, 16.5 for the A/Pw matrix, and 11 for the
Multistate matrix. Wilcoxon signed rank tests (Templeton, 1983) showed that two of the three constrained
topologies were significantly longer than the unconstrained trees (Table 3). The exception was the
Multistate data set assessing Ivanov’s (1963) hypothesis, and this may be due to the very small data set.
When the same method was applied to Webb’s (196413)
taxon set (also with uninformative characters excluded
i.e. A/P characters 1, 2, 7, 9-22, 25, 26, 30-37, 40, 41,
44 or Multistate characters 1,5-15, 18,20-26,28,30),
then this resulted in 5 shortest trees of length 25 for
the A/Pe matrix, 202 shortest trees of length 22.5 for
the A/Pw trees, and 2 shortest trees of length 14 for
the Multistate trees. As for the restricted analyses
based on Ivanov’s (1963) hypothesis, these topologies
were also congruent with the complete analyses presented here. In contrast, when applyingWebb’s (196413)
topology, and Sclemlinurn is assumed to be the sister
group to the rest of Siboglinidae, the lengths were 39
for the A/pe matrix, 34 for the A/pw matrix and 22 for
the Multistate matrix (Table 3). Wilcoxon signed rank
tests showed that these constrained topologies based
on Webb (1964b) were significantly longer than the
unconstrained trees (Table 3).
While both the hypotheses expressed in Figure 5
can be disregarded as not being parsimonious explanations of the available data, the overall congruence
in the results found here (Figs 2 4 ) suggests some
new conclusions may be drawn. The plesiomorphic
condition for palps found in all analyses was for there
to be a single pair, in agreement with Webb (1964b).
From the paired condition, the ‘numerous’ palp condition appears to have developed twice, once for Vestimentifera and once for a large unnamed clade in
Frenulata (Figs 4,5). Within this frenulate clade there
have been subsequent reductions to two palps again
(Diplobrachia) or to a single palp (Siboglinurn and
Unibrachiurn). Other plesiomorphic conditions for siboglinids that subsequently transform would appear
to be:
(1) The frenulum, which has become scattered plaques
on the vestimentum of vestimentiferans. Interestingly, Sclemlinurn major Southward, (1972)
has only scattered plaques instead of a frenulum.
(2) The tube with a collapsible anterior end has
changed into a more rigid one with funnels in
vestimentiferans, Choanophorus and the clade
comprised of Larnellisabella, Siphonobrachia, and
Spimbrachia.
There have been two explicit phylogenetic hypotheses proposed for Vestimentifera. Jones (1988)
illustrated his Linnaean taxonomy of the group in a
dendrogram format (shown in Table 1). The results of
the present A/P analyses do not support his hypothesis
in that Riftia (Axonobranchia) is nested within the
Basibranchia. Also the proposed sister group relationship between Teunia and Oasisia was not recovered. However, the clades comprised of
(Lurnellibrachia, Escarpia) and (Oasisia, Teunia,
Ridgeia) proposed by Jones (1988) were found in the
A/p analyses.
Black et al. (1997) and Halanych et al. (1998) found
that vestimentiferans that live at ‘cold-seeps’ (Escarpia, Lurnellibrachia) formed a grade with respect
to the remaining vestimentiferans, all of which are
associated with hydrothermal vents. It should be noted
that neither of these two studies, based on molecular
sequences, included data for Alaysia or Amuestia,
both of which are associated with hydrothermal vents
(Southward, 1991; Southward & Galkin, 1997). In
contrast to the analyses based on molecular data, the
results from the A/p analyses here both show that the
cold-seep taxa form a clade that is the sister group
CLADISTICS OF SIBOGLINIDAE (POLYCHAETA)
71
Table 3. Comparison of tree lengths using the taxa shown in Ivanov’s
(1963) and Webb‘s (1964b) respective phylogenetic hypotheses (Fig. 5).
Analyses were either: (1) constrained to their topologies (Fig. 5), or (2)
unconstrained parsimony analyses. Only the taxa shown by Webb or
Ivanov were used, and characters that were uninformative for these
restricted taxon sets were excluded from the A/P or Multistate matrix
(see text). Wilcoxon signed rank tests (Templeton, 1983) showed that
constrained topologies were significantlylonger than the unconstrained
trees in 5 out of the 6 analyses. The exception was the Multistate data
set assessing Ivanov’s (1963) hypothesis and this may be due to the
very small data set
A/Pe unconstrained
A/Pe
constrained
A/pw
A/pw
unconstrained
constrained
Multistate unconstrained
Multistate constrained
t o the hydrothermal-vent taxa. Black et al. (1997)
proposed that the hydrothermal-vent associated fauna
evolved from vestimentiferan ancestors associated
with cold seeps. While the topology of vestimentiferan
relationships found here differs from that of Black et
al. (1997), consideration of the habitats occupied by
other members of Siboglinidaewould suggest that their
hypothesis is correct. The lack of resolution found in
the Multistate analysis suggests that further detailed
study of vestimentiferans is required, particularly on
Alaysia and Arcouestia.
SYSTEMATICS
The first issue that requires comment is the formal
name for the group under study. As outlined in the
Introduction, Rouse & Fauchald (1997) and McHugh
(1997) suggested that Pogonophora plus Vestimentifera, having been inferred to have a sister group
among polychaete annelids, should revert to the name
Siboglinidae. Rouse & Fauchald (1997) justified their
recommendation by stating that the name Pogonophora may become misleading when applied as a
subgroup name within polychaetes. By changing the
name t o the first name erected for the group, Siboglinidae, a ‘fresh‘ start is made in terms of the
taxonomic status of the group. This suggestion has
been endorsed in several recent papers (Halanychet al.,
1998;Boore &Brown, 2000), and is adopted throughout
this paper. However, within the Pogonophora-
Ivanov, 1963
(Fig. 5A)
Webb, 1964b
(Fig. 5B)
12 steps
20 steps
P<O .0384*
25 steps
39 steps
P<O .0039*
9.5 steps
16.5 steps
P<0.0384*
22.5 steps
34 steps
P<0.0261*
6 steps
11 steps
14 steps
22 steps
P<O.1025
P<0.0231*
Vestimentifera clade, there is currently 13family group
taxa, and the current rules of nomenclature would
then enforce 12 of these to be synonymized with the
oldest available name, Siboglinidae. There are also
additional nomenclatural problems in that well-defined names such as Vestimentifera have now been
shown t o represent subgroups within Siboglinidae.
An alternative to the Linnaean system is to apply the
names within the framework of phylogenetic taxonomy
(e.g. de Queiroz & Gauthier, 1992). The name Siboglinidae can be retained and given a phylogenetic
definition, instead of a Linnaean one (see below). Furthermore, the abandonment of all traditional suprageneric names within Siboglinidae, except for
Vestimentifera, Monilifera, and Frenulata is recommended (the relationships within the less inclusive
groupings are not analysed here, and will require
separate studies and revisions). The usefulness in
selecting the names Vestimentifera, Monilifera, and
Frenulata for the major subgroups of Siboglinidae lies
in that their circumscription (see Fig. 2) is largely
consistent with recent, traditional taxonomy (e.g.
Ivanov, 1991). The previously 12 ‘sunk’ family names
will, in the absence of Linnaean ranks, not have to be
synonymized they will instead simply be considered as
currently unused names for parts within Siboglinidae.
They may be activated later following further study
and better resolution. Here a conservative approach
is taken and only four well-supportedtaxon names are
defined.
72
G.W. ROUSE
Based on the results here from all three fonns of
analysis I define Siboglinidae as the first polychaete,
and all its descendants, to have an occluded gut (with
the endoderm presumably occupied by chemoautotrophic bacteria) as seen in the holotype of Riftia
pachyptila Jones, 1981a. Only one of the several apomorphies that support this clade (others include a
frenulum, trunk, opisthosoma, uncini with opposing
teeth, and collapsible tube, see Figs 3, 4) is used to
define the taxon name. If all of the apomorphies were
used to define Siboglinidae, then essentially the last
of these features to evolve would actually identify the
common ancestor linked to the name Siboglinidae.
New taxa may be described that do not have all these
features and so would be excluded from the taxon. The
choice of which apomorphy to use is hence arbitrary,
but I suggest that the presence of an occluded gut may
be a key feature in the evolution of this group and is
an appropriate feature to use for the definition of the
name.
In all analyses, the same two major clades were
found within Siboglinidae. In one, Sclemlinum was
placed as the sister group to vestimentiferans. Thus,
Vestimentifera represents a derived clade of Siboglinidae, and its exclusion from this group, as proposed by Jones (1985a,b), cannot be sustained. This
result was foreshadowed by Southward (1993: 332)
who noted that several features of Sckmlinum ‘suggest
a link with the Obturata (Vestimentifera)”. Ivanov
(1991)had also noted similaritiesbetween Sclemlinum
and vestimentiferans and removed the former from
Frenulata. However, rather than group Sclemlinum
with vestimentiferans, he placed it into a new taxon,
Monilifera, with equal rank to Frenulata and Vestimentifera. I suggest, rather than make a new name,
that the name Monilifera now be applied to the Sckmlinum plus Vestimentiferaclade. The taxon name Monilifera can be defined based on apomorphy-based
system such that it is the first siboglinid, and all its
descendants, to have rings of chaetae (uncini) in the
opisthosoma, as seen in the holotype of Sclemlinum
magdaknae Southward, 1972. A number of other apomorphies from the A/P analyses could also be used to
aid in define this taxon but these ended as being
ambiguous transformations in the Multistate analysis
(see Fig. 4). Within Monilifera, the taxon name Vestimentifera can be defined as the first siboglinid and
all its descendant to have a vestimentum as seen in
the holotype of Riftia pachyptia.
As discussed above, the results indicate that Jones’s
division of Vestimentifera into Axonobranchia and Basibranchia has little utility. Firstly, Ridgeia is the only
member of Axonobranchia and so Axonobranchia is
an ‘empty’ taxon. Also, since in the A / p analyses,
Axonobranchia is always nested among the other vestimentiferans, Basibranchia is paraphyletic. In the
Multistate analyses there is so much topological variation among vestimentiferans that no further subdivision of the group can be made. I recommend
abandoning Axonobranchia and Basibranchia as taxon
names. I also recommend that the vestimentiferan
names of family rank also be abandoned.Firstly, under
the current Linnaean system of nomenclature, these
names are all junior synonyms of Siboglinidae. Also,
with the exception of Tevniidae containing Oasisia and
Tevnia, they are all monotypic, and hence ‘empty’taxa.
Tevniidae was also shown to be paraphyletic in the A/
P analyses.
The taxon Frenulata, as formulated by Ivanov
(1991), was found in all analyses here, and I recommend that the name Frenulata continue t o be
applied as a clade name within Siboglinidae. This
grouping represents all Siboglinidae, with the exception of Sclemlinum and vestimentiferans. The
monophyly of this clade was supported by numerous
synapomorphies, and as a taxon Frenulata can be
defined as the first siboglinid, and all its descendants,
t o have a mid-trunk girdle, as seen in the holotype of
Siboglinum weberi (see Southward, 1961). The presence of a frenulum, which was used by Webb (1969a)to
name the taxon Frenulata is actually a plesiomorphic
feature for Siboglinidae.
Within Frenulata the taxon Athecanephria, erected
by Ivanov was not supported in this analysis. Rather
Athecanephria taxa (see Table 1) consistently formed
a grade, a result actually implied by Webb’s (1964b)
representation of the group’s phylogeny (Fig. 5B). If
Choanophorus is not considered, Thecanephria did
form a clade in all A/Pe and Multistate analyses, but
this was only supportedby the loss of ventral glandular
shields. In the A/pw analysis the variable placement
of Diplobrachia means that Thecanephria was not
consistently supported as monophyletic. Thecanephria
and Athecanephriawere erectedbased on the structure
of the anterior nephridia by Ivanov (1957), but there
has never been a comprehensive survey t o assess
whether this is a useful systematic feature. Instead of
nephridial organization, the shape of spermatophores
has usually been used as a guide for the placement of
taxa into either Athecanephria (with narrow ‘spindleshaped spermathecae) and Thecanephria (with broad
‘leaf-shaped’ spermathecae). However in the present
study, the presence of ‘leaf-shaped spermathecae did
not serve as a synapomorphy for Thecanephria, since
Zenkvitchianu has narrow spermathecae (Figs 3, 4).
This means that ‘leaf-shaped spermatophoresevclved
from a ‘spindle-shapedcondition within Thecanephria.
Since Athecanephria is consistently paraphyletic, and
the monophyly of Thecanephria is not indicated, I
recommend abandoning these taxon names.
The family level taxa used by Ivanov (1963) that
CLADISTICS OF SIBOGLINIDAE (POLYCHAETA)
contain more than one genus; Lamellisabellidae, Oligobrachiidae, Polybrachiidae, and Siboglinidae (see
Table l),were consistently found t o be paraphyletic or
polyphyletic in this study. Since the recommendation
that the name Siboglinidae be adopted for the ingroup
taxa in this analysis has been followed here, all taxa
of family rank are t o be considered synonyms of Siboglinidae anyway. However, the fact that none of the
names of family rank, either in Frenulata or Vestimentifera, was found to be monophyletic lends support to their elimination as formal names. The
exceptions are, of course, those families that contain
a single genus and hence are essentially ‘empty’taxa
with no utility. Given the fact that there was a lack of
resolution and some difference between the analyses
in terms of the relationships within Frenulata, I suggest that no other taxa within this clade be named at
this time. Further study is required on the taxa at
generic rank, since several may well be paraphyletic
assemblages.
CONCLUSIONS
The results shown here show a number of morphological features that support the monophyly of Siboglinidae. They also show clear placement of the
vestimentiferan clade as the sister group to Sclemlinum within Siboglinidae.
While the name Pogonophora is eliminated here
as a taxon name, there is no reason why the name
‘pogonophores’ or ’beard worms’ cannot be used as
informal name, much the same way as ‘ragworms’and
‘fanworms’are used for the polychaete taxa Nereididae
and Sabellidae respectively. The taxon names Frenulata, Monilifera and Vestimentifera are retained and
are defined according t o principles of phylogenetic
taxonomy. They are all contained within the taxon
Siboglinidae. All other names, with the exception of
those with the rank of genus or species, are considered
here to be redundant because they are ’empty’ taxa,
or represent paraphyletic or polyphyletic assemblages.
NOTE ADDED IN PROOF
A new paper (Halanych, Feldman & Vrijenhoek, 2001)
based on molecular evidence using 18s rDNA and 16s
rDNA has shown that Sclemlinum brattstmrni is closer
to Vestimentifera than to other Siboglinidae. This
result corroborates the findings shown in this paper
based on morphology.
ACKNOWLEDGEMENTS
Thanks t o D. J. Patterson (University of Sydney) for
facilities and advice. Also thanks t o A. Simpson (University of Sydney) and Fredrik Pleijel (Museum National &Histoire Naturelle) for comments on a draft of
73
the manuscript and t o two anonymous reviewers for
their interesting comments. This study was supported
by an Australian Research Council QEII Research
Fellowship.
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(24) Anterior of segment 1 (or 2) trunk with ridges and
pyriform glands.
(25) Mid-part of segment 1 (or 2) (Trunk) with uncinal
girdle.
(26) Segment 1 (or 2) (Trunk) with uncinal girdle posteriorly.
(27) Segment 1 (or 2) (Trunk) with zone of thickened
papillae.
(28) Segment 1 (or 2) (Trunk) with scattered papillae.
(29) Posterior of segment 1 (or 2) (trunk) with raised
ventral glandular shields.
(30) Posterior of segment 1 (or 2) (trunk) with papillae
dorsal papillae in rows or a line.
(31) Marked opisthosomal diaphragm.
(32) Opisthosoma.
(33) Posterior segments with uncini only.
(34) Uncini with teeth in two groups facing opposite
directions.
(35) Posterior chaetae ‘peg-like’.
(36) Posterior chaetae form rings.
(37) Spermatophores.
(38) Spermatophores broad (leaf-like).
(39) Spermatophore narrow (spindle-like).
(40) Spermatozeugmata.
(41) Gut occluded.
(42) Tube rigid with funnels.
(43) Tube membranous and collapses anteriorly.
(44)Tube buried in sediment.
(B) Multistate characters
APPENDIX 1
CHARACTERS USED FOR THE A / p AND MUETISTATE
ANALYSES
(A) Absent/Present characters
All characters are binary with 0 for Absent and 1 for
Present. Taxa where the condition for a character was
unknown were scored with ‘?.
(1) Prostomium indiscernible.
(2) Adult with single palp.
(3) Adult with a pair of palps.
(4) Adult with ‘numerous’ palps.
(5) Pinnules on palps.
(6) Palp pinnules single-celled.
(7) Palp pinnules multi-celled.
(8) ‘Numerous’palps fused via cuticle.
(9) Some palps form outer sheath lamellae.
(10) Obturaculum.
(11) Obturacular musculature parasagittal.
(12) Obturacular musculature frontal.
(13) Obturaculum with a n axial rod.
(14) Obturaculum with terminal saucers.
(15) Obturaculum with terminal crust.
(16) Obturaculum stalk grooved.
(17) Obturaculum stalk ridged.
(18) Vestimentum.
(19) Frenulum.
(20) Single exit for anterior pair of nephridia.
(21) Clear diaphragm groove a t beginning of trunk.
(22) Segment 1 (or 2) forms elongate trunk.
(23) Anterior of segment 1 (or 2) trunk with metameric
papillae.
Some characters are binary and then there are multistate characters subsidiary to these in some sense.
Scoring for taxa for the less general characters when
they were scored as absent (0) for the more general
characters is a ‘-’. Taxa where the condition for a character was unknown were scored with ‘?.
(1) Prostomium indiscernible: (0) Absent, (1) Present
(2) Adult palps: (0) Pair of palps, (1) Single palp, (2)
‘Numerous’ palps
(3) Palpal pinnules: (0) Absent, (1) Present (multicelled), (2) Present (single-celled)
(4) Palps fused (0) Absent, (1) Present
(5) Outer sheath lamellae: (0) Absent, (1) Present
(6) Obturaculum: (0) Absent, (1) Present
(7) Obturaculum musculature: (0) Parasagittal, (1)
Frontal
(8) Obturaculum with axial rod: (0)Absent, (1)Present
(9) Obturaculum axial rod with: (0) Saucers, (1) Crust
(10) Obturaculum s t a k (0) Grooved, (1) Ridged
(11) Vestimentum: (0) Absent, (1) Present
(12) Frenulum: (0) Absent, (1) Present, (2) Scattered
plaques only
(13) Single exit for pair of anterior nephridia: (0)Absent,
(1) Resent
(14) Diaphragm with clear external groove: (0) Absent,
(1) Present
(15) Segment 1 (or 2) forms elongate trunk: (0) Absent,
(1) Present
(16) Anterior segment 1 (or 2) (Trunk) with glands: (0)
Smooth, (1) Ridges, (2) Metameric papillae
(17) Papillae in anterior segment 1 (or 2) (Trunk) : (0)
Absent, (1) Thickened zone, (1) Scattered
CLADISTICS OF SIBOGLINIDAE (POLYCHAETA)
Segment 1 (or 2) (Trunk) with uncinal girdle: (0)
Absent, (1) Present middle, (1) Present posteriorly
Ventral glandular shields: (0) Absent, (1) Present
Posterior of segment 1 (or 2) (trunk) with papillae:
(0) Absent, (1) Line or Rows, (2) Scattered
Opisthosoma: (0) Absent, (1) Present
Opisthosomal diaphragm: (0) Absent, (1) Present
Posterior segment chaetae: (0) Uncini and others,
(1) All uncini, (2) ‘Peg-like’chaetae
Posterior chaetae: (0) Notopodial and neuropodial,
(1) Form rings
Uncini with teeth: (0) Facing same direction, (1)
Two groups facing opposite directions.
Sperm packaging: (0) Absent, (1) Spermatophore,
(2) Spermatozeugmata
Spermatophore shape: (0) Narrow (spindle), (1)
Broad (leaf)
Gut occluded: (0) Absent, (1) Present
Tube: (0) Mixture of organic and inorganic, (1)
Organic and anterior collapses, (2) Organic with
rigid opening
Tube lies in sediment: (0) Absent, (1) Present
77
Scoring largely based on Webb (1969a), van der Land &
Nerrevang (1975). An opisthosoma has been found in
Lamellibrachia columna and L. satsuma (Miura et al.,
1997; Southward, 1991).
Oasisia Jones, 1985a
Oasisia alvinae Jones, 1985a; only nominal species.
Scoringbased on Jones (1985a) and Southward & Galkin
(1997). Nothing is known about sperm packaging.
Ridgeia Jones, 1985a
Ridgeia piscesae Jones, 1985a; only nominal species
after Southward et al. (1995) synonymized R. phaeophiale Jones, 1985a with R. piscesae.
Scoring based on Jones (1985a), Southward & Coates
(1989), and Southward & Galkin (1997).
Riftia Jones, 1981a
Riftia pachyptila Jones, 1981a; only nominal species.
Scoring based on Jones (1985a), Jones & Gardiner (1985)
and Southward & Galkin (1997).
Tevnia Jones, 1985a
Tevnia jerichonana Jones, 1985a; only nominal species.
Scoringbased on Jones (1985a) and Southward & Galkin
(1997). Nothing is known about sperm packaging.
MONILIFERA
APPENDIX 2
NOTES ON TERMINALS AND SCORING OF
SIBOGLINIDAE
Terminal taxa are listed in alphabetical order under the
more inclusive taxa adopted here; Monilifera containing
Sclemlinum plus Vestimentifera, and Frenulata containing all other Siboglinidae. The type species of the
genera are listed, along with information about how
many other taxa are currently included in the taxon.
All references that were used in scoring are cited and
details are given about scoring where there was ambiguity in the descriptions or polymorphism within the
taxon, in which case data from the type species was
used.
MONILIFERA
VESTIMENTIFERA
Alaysia Southward, 1991
Alaysia spiralis Southward, 1991; only nominal species.
Scoring based on Southward (1991) and Southward &
Galkin (1997). There is no information about the presence of pinnules on the palps, the musculature of the
obturaculum, nephridia, or sperm packaging.
Arcovestia Southward & Galkin, 1997
Arcovestia ivanovi Southward & Galkin, 1997; only nominal species.
Scoring based on Southward & Galkin (1997). There is
no information about the presence of pinnules on the
palps, the musculature of the obturaculum, nephridia,
or sperm packaging.
Escarpia Jones 1985a
Escarpia spicata Jones 1985a and Escarpia laminata
Jones 1985a.
Scoring based on (Jones, 1985a) and Southward & Galkin, (1997). There is no information about the posterior
end of the body, or sperm packaging.
Lamellibrachia Webb, 1969a
Lamellibrachia barhami Webb, 1969a and four other
nominal species (see Miura et al., 1997).
Sclemlinum Southward, 1961
Sclemlinum sibogae Southward, 1961; five further nominal species (see Ivanov & Selivanova, 1992; Southward,
1972).
Scoring based on Southward (1972), Ivanov & Selivanova (1992), and Webb (1964a; 1964~).Members of
Sclemlinum all have a pair of elongate palps that are
easily broken (Webb, 1964a). A frenulum is present as a
row of cuticular plates in some taxa, though Sclemlinum
major Southward, 1972 has only scattered plaques, as
in vestimentiferans. It is assumed here that a frenulum
is the plesiomorphic condition for Sclemlinum. There is
no clear diaphragm identifying the beginning of the
trunk according to (Webb, 1964a),but Southward (1980)
noted an oblique band of muscle that seemed to be the
diaphragm, though there is no external sign of this.
Ivanov (1994) argued that the region bearing the
frenulum is extremely long in Sclemlinum and that a
diaphragm is present. In this study the criterion adopted
is based on a clear external marking identifying the
diaphragm, and Sclemlinum does not have this. Further
investigation is, however, required. Southward (1968)
suggested the anterior part of the trunk has two lines
of pyriform glands. Southward (1972) showed that there
are uncini a t the very end of the trunk, immediately in
front of the first opisthosomal segment. Southward
(1961) originally described spermatophores in Sclerolinum sibogae, but Southward (1971b) notes there is
no spermatophore. Whether the sperm are packaged as
spermatozeugmata is not known. For the Multistate
matrix this meant that Sclemlinum was scored as having
either free spawning or spermatozeugmata.
FRENULATA
Birstenia Ivanov, 1952
Birstenia vitjasi Ivanov, 1952; only nominal species.
Scoring based on Ivanov (1963). The posterior end is
unknown.
Choanophorus Bubko, 1965
78
G. W. ROUSE
Choanophorus indicus Bubko, 1965; only nominal species.
Scoring based on Bubko (1965) and Southward (1969).
The spermatophores are described as 'band-shaped' by
Bubko (1965) and this is treated here as being the
narrow condition.
Crassibrachia Southward, 1968
Crassibrachia sandersi Southward, 1968, and C. bmsiliensis Southward (1968).
Scoring based on Southward (1968). The spermatophores are narrow and, though they are slightly
flattened, they are not given the leaf-like state. Rather
they are similar to the spermatophores of Choanophorus,
and Siphonobrachia, which seem to fall between the
two states defined by Ivanov (1963). For the purposes
of this study all these taxa were considered as having
narrow spermatophores.
Cyclobrachia Ivanov, 1960
Cyclobrachiaauriculata Ivanov, 1960; only nominal species.
Scoring based on Ivanov (1963). There are nine palps
and this is regarded as being 'numerous'. Ivanov (1963:
366) wrote that the palps are free but closed a t the base.
Southward (1993:) states that the palps are closed and
this is interpreted as meaning fused. The uncini of the
girdle have teeth that all face in the same direction
(Ivanov, 1963: fig. 145). The posterior end is unknown.
Diplobrachia Ivanov, 1960
Diplobrachia japonica Ivanov, 1960; five other nominal
species described (see Southward & Brattegard, 1968).
Scoring based on Ivanov (1963) and Southward & Brattegard (1968). The number of palps varies within Diplobrachia with some taxa having three or four palps
and others having a pair. A pair of palps was coded as
present here but further study is required on this taxon.
The posterior end is unknown.
Galathealinum Kirkegaard, 1956
Galathealinum bruuni Kirkegaard, 1956; three other
nominal species (see Adegoke, 1967). Webb (1971) suggested that two members of Galathealinum be removed
from this taxon and they were not considered in scoring
here. Scoring otherwise based on Ivanov (1963). The
middle and posterior end is unknown.
Heptabrachia Ivanov, 1952
Heptabrachia abyssicola Ivanov, 1952; six other species
in Ivanov (1963). However, Heptabrachia canadensis
Ivanov, 1962 was transferred by Southward (1969) to
Polybrachia. Scoring based on Ivanov (1963). The posterior end is unknown.
Lamellisabella Uschakov, 1933
Lamellisabella zachsi Uschakov, 1933; six other nominal
species (see Southward, 1978b).
Scoring based on Ivanov (1963). The posterior end is
unknown.
Nereilinum Ivanov, 1961
Nereilinum murmanicum Ivanov, 1961 and N. punctatum Nielsen, 1965
Scoring based on Ivanov (1963; 1975a). The presence of
pinnules on the palps and raised ventral glandular areas
on the posterior trunk was based on N. murmanicum,
though N. punctatum Nielsen, 1965 lacks them.
Oligobrachia Ivanov, 1957
Oligobrachia doglei Ivanov, 1957; seven other nominal
species (see Southward, 1978al.
Scoring based on Ivanov (1963) and Southward (1978a).
Polybrachia Ivanov, 1952
Polybrachia annulata Ivanov, 1952; three nominal species in Ivanov 1963), including Kmmpolineum galathae
Kirkegaard, 1956. Southward & Brattegard (1968) described two other members and Southward (1969) transferred Heptabrachia canadensis to Polybrachia, making
a total of seven nominal species.
Scoring based on Ivanov (1963), Southward (1969).
SibogZinoides Ivanov, 1960
Siboglinoicles dibrachia Ivanov, 1960;two other nominal
species (see Ivanov, 1971; Southward, 1971b).
Scoring based on Ivanov (1963) and Southward (1971b).
The posterior end is unknown.
Siboglinum Caullery, 1914
Siboglinum weberi Caullery, 1914; 37 other nominal
species listed in Ivanov (1963). Southward (1961) resolved the issue concerning the designation of the name
S. weberi, since Caullery (1914) had actually grouped
16 different taxa under this name. Southward (1971b)
listed additional descriptions to bring the total to 51.
Subsequent descriptions (Fliigel, 1990; Flugel &
Callsen-Cencic, 1993; Fliigel & Langhof, 1983; Ivanov,
1971; Southward, 1971a, 1972, 1975a) bring the total
of described nominal species to 65. Scoring is based
on Ivanov (1963) and Webb (1964d). Although some
members of Siboglinum have uncini with teeth all face
in the same direction, most have two groups of teeth
that oppose each other and this state is used in this
study.
Siphonobrachia Nielsen, 1965
Siphonobrachia ilyophora Nielsen, 1965 and S. laeuensis Southward, 1991.
Scoring based on (Gupta & Little, 1969; Nielsen, 1965;
Southward, 1991). Although Nielsen (1965) suggests
that S. ilyphora may have a zone of thickened papillae,
it does not appear to be present in the relevant figures
and was not found in S. lauensis Southward, 1991. The
uncini of S. ilyphora all face in the same direction
whereas those of S. lauensis oppose each other and the
state in the latter taxon is used in this study. The
spermatophore is known only for S. lauensis and was
described as being narrow and compared with those of
Oligobrachia by Southward (1991). The opisthosoma
was described for S. lauensis.
Spimbrachia Ivanov, 1952
Spimbrachia grandis Ivanov, 1952; one other nominal
species (see Ivanov, 1963).
Scoring based on Ivanov (1963). The posterior end is
Unknown.
Unibrachium Southward, 1972
Unibrachium colombianum Southward, 1972; one other
nominal species (see Southward, 1978a).
Scoring based on Southward (1972, 1975a). Unibrachium colombianum has a zone of thickened papillae
and U.tenuifrenum Southward, 1975a seems to lack it.
The condition in U. columbianum was used here. The
posterior end is unknown.
Zenkevitchiam Ivanov, 1957
Zenkvitchianu longissima Ivanov, 1957; only nominal
species.
Scoringbased on Ivanov (1963). The spermatophores are
narrow but were compared with those of Spimbrachia by
Ivanov (1963) i.e. leaf-shaped. For this study they are
scored as narrow. The posterior end is unknown.
Sabellariidae
Alaysia
Amvestia
Escarpia
Lamellibrachia
Oasisia
Tevnia
Ridgeia
Riftia
Scleml inum
Birs teinia
Choanophorus
Crassibrachia
Cyclobrachia
Diplobrachia
Galathealinum
Heptabrachia
Lamellisa be1la
Oligobrachia
Nereilinum
Polybrachia
Si boglinoia!es
Siboglinum
Siphonobrachia
Spimbrachia
Unibrachium
Zenkevitchiana
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
1
0
0
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
1
0
0
0
0
1
0
1
0
0
0
0
0
1
0
0
0
0
0
0
0
0
1
0
1
0
1
0
1
1
1
1
0
1
0
0
1
1
0
1
0
1
1
1
1
1
1
1
1
0
1
0
0
?
1
1
1
1
1
0
1
1
1
1
1
1
1
0
1
1
1
1
1
1
1
1
0
1
0
0
?
1
1
1
1
1
0
1
1
1
1
1
1
1
0
?
?
0
0
0
0
0
0
0
1
0
0
?
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
1
0
0
0
1
0
0
0
0
0
1
1
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
?
?
0
0
1
1
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0 0 0 0 0 1 ? 1 1 1 0 1 0 1 0 1 1 1 1 0 1 1 0 1 0 1 0 1 1 0 1
0 0 0 0 0 1 ? 1 1 1 0 1 0 1 0 1 1 1 1 0 1 1 0 1 0 1 0 1 0 1 1
0 0 0 0 0 1 ? 1 1 1 0 1 0 0 1 0 1 ? ? ? 0 ? ? 1 1 0 0 1 0 1 1
0 0 0 0 0 1 ? 1 1 1 0 1 0 1 0 0 1 ? ? ? 1 ? ? 1 1 0 0 1 0 1 1
0 0 0 0 0 1 ? 1 1 1 0 ? ? 1 0 ? ? ? ? ? ? ? ? 1 1 0 0 1 0 1 1
0 0 0 0 0 1 ? 1 1 1 0 1 0 1 0 0 1 ? ? ? 1 ? ? 1 1 0 0 1 0 1 1
0 0 0 0 0 1 0 1 1 1 0 1 0 0 1 0 1 ? ? ? 1 ? ? 1 1 0 0 1 1 0 1
0 0 0 0 0 1 0 1 1 0 1 1 0 1 0 1 1 1 1 0 1 1 0 1 0 1 0 1 0 1 1
0 0 0 0 0 1 ? 1 1 0 1 1 0 1 0 1 1 1 1 0 1 1 0 1 0 1 0 1 0 1 1
0 0 0 0 0 1 ? 1 1 1 0 1 0 1 0 0 1 1 1 0 1 1 0 1 1 0 0 1 0 1 1
0 0 0 0 0 1 ? 1 1 1 0 1 0 0 1 1 1 ? ? ? 1 ? ? 1 0 1 0 1 0 1 1
0 0 0 0 0 1 0 1 1 1 0 1 0 1 0 1 1 1 1 0 1 1 0 1 0 1 0 1 0 1 1
0 0 0 0 0 1 0 1 1 1 0 1 0 0 1 0 1 ? 1 0 0 1 0 1 0 1 0 1 1 0 1
0 0 0 0 0 1 ? 1 1 1 0 1 0 0 1 0 1 ? ? ? 1 ? ? 1 1 0 0 1 1 0 1
0 0 0 0 0 1 ? 1 1 0 1 1 0 1 0 ? ? ? ? ? 1 ? ? 1 0 1 0 1 0 1 1
0 0 0 0 0 1 ? 1 1 1 0 1 0 0 1 0 1 ? ? ? 1 ? ? 1 0 1 0 1 0 1 1
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
? 0 0 0 1 0 1 0 ? 0 1 0 0 0 1 0 1 0 0 0 1 1 1 0 1 ? ? ? ? 1 1 0 0
? 0 0 0 1 0 1 0 0 0 1 0 0 0 1 0 1 0 0 0 1 1 1 0 1 ? ? ? ? 1 1 0 0
1 1 0 1 0 1 1 0 1 0 1 0 0 0 1 0 1 0 0 ? ? ? ? ? ? ? ? ? ? 1 1 0 ?
1 0 0 0 0 1 1 0 1 0 1 0 0 0 1 0 1 0 0 0 1 1 1 0 1 0 0 0 1 1 1 0 0
0 1 1 0 1 0 1 0 0 0 1 0 0 0 1 0 1 0 0 0 1 1 1 0 1 ? ? ? ? 1 1 0 0
0 1 0 1 1 0 1 0 0 0 1 0 0 0 1 0 1 0 0 0 1 1 1 0 1 ? ? ? ? 1 1 0 0
1 1 1 0 1 0 1 0 0 0 1 0 0 0 1 0 1 0 0 0 1 1 1 0 1 0 0 0 1 1 1 0 0
0 0 0 0 1 0 1 0 0 0 1 0 0 0 1 0 1 0 0 0 1 1 1 0 1 0 0 0 1 1 1 0 0
0 0 0 0 0 0 0 1 ? 0 1 0 1 0 1 0 1 0 0 0 1 1 1 0 1 0 0 0 ? 1 0 1 0
0 0 0 0 0 0 0 1 0 1 1 1 0 1 0 1 0 ? ? ? ? ? ? ? ? 1 0 1 0 1 0 1 1
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 4041 42 43 44
(A) Matrix of A/p coding scores used in both A/Pe and A/pw analyses. Present is coded with ‘1’.Unknown is coded with ‘?.
MATRICES
APPENDIX 3
80
G. W. ROUSE
(B) Matrix of Multistate coding scores used in the multistate analysis. The OR separator 7' is used for character
26 (Sperm packaging) for Sclerolinum since the presence of spermatophores could be excluded. Unknown is
coded with '?' and inapplicable with '-'.
1 2 3 4 5 6 7 8 9 101112131415161718192021222324252627282930
Sabellariidae
Alaysia
Arcovestia
Escarpia
Lamellibrachia
Oasisia
Tevnia
Ridgeia
Riftia
Sclemlinum
Birsteinia
Choanophorus
Crassibrachia
Cyclobrachia
Diplobrachia
Galathealinum
Heptabrachia
Lamellisa bella
Nereilinum
01igobrachia
Polybrachia
Si boglinoides
Si boglinum
Siphono brachia
Spimbrachia
Unibrachium
Zenkevitchiana
0
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
2
2
2
2
2
2
2
2
0
2
2
0
2
0
2
2
2
0
2
2
0
1
2
2
1
2
0
1
1
1
1
1
1
1
1
0
2
0
0
?
2
2
2
2
0
2
2
2
2
2
2
2
2
0 0 - - - - - 0 0 0 0 0 0 0 0 0 0 0 - 0 0 0 0 - 0 0 0
1 1 1 ? 0 - 1 1 2 ? 0 1 ? 2 2 0 2 1 0 1 1 1 ? ? 1 2 0
1 0 1 ? 0 - 1 1 2 0 0 1 ? 2 2 0 2 1 0 1 1 1 ? ? 1 2 0
1 0 1 1 1 1 0 1 2 1 0 1 3 2 2 0 2 ? ? ? ? 1 ? ? 1 2 ?
1 1 1 1 0 - 0 1 2 1 0 1 3 2 2 0 2 1 0 1 1 1 2 - 1 2 0
1 0 1 0 1 0 1 1 2 0 0 1 3 2 2 0 2 1 0 1 1 1 ? ? 1 2 0
1 0 1 0 1 1 1 1 2 0 0 1 ? 2 2 0 2 1 0 1 1 1 ? ? 1 2 0
1 0 1 1 1 0 1 1 2 0 0 1 ? 2 2 0 2 1 0 1 1 1 2 - 1 2 0
1 0 1 0 0 - 1 1 2 0 0 1 3 2 2 0 2 1 0 1 1 1 2 - 1 2 0
0 - 0 - - - - 0 1 ? 0 1 1 2 2 0 2 1 0 1 1 1 2 - 1 1 0
0 0 0 - - - - 0 1 ? 1 1 2 1 1 ? ? ? ? ? ? 1 1 0 1 1 1
0 0 0 - - - - 0 1 ? 1 1 2 1 1 1 1 1 1 2 0 1 1 0 1 2 1
0 - 0 - - - - 0 1 ? 1 1 2 1 1 1 1 1 1 2 0 1 1 0 1 1 1
1 0 0 - - - - 0 1 ? 1 1 2 2 1 0 1 ? ? ? ? 0 1 1 1 1 1
0 - 0 - - - - 0 1 ? 1 1 2 1 1 0 1 ? ? ? ? 1 1 1 1 1 1
0 0 0 - - - - 0 1 ? 1 1 2 1 ? ? ? ? ? ? ? ? 1 1 1 1 1
0 0 0 - - - - 0 1 ? 1 1 2 1 1 0 1 ? ? ? ? 1 1 1 1 1 1
1 0 0 - - - - 0 1 0 1 1 2 2 1 0 1 ? ? ? ? 1 1 1 1 2 1
0 - 0 - - - - 0 1 ? 1 1 1 1 1 1 1 1 1 2 0 1 1 0 1 1 1
0 0 0 - - - - 0 1 0 1 1 1 1 1 1 1 1 1 2 0 1 1 0 1 1 1
0 0 0 - - - - 0 1 ? 1 1 2 1 1 0 1 1 1 2 0 1 1 1 1 1 1
0 - 0 - - - - 0 1 ? 1 1 2 2 1 1 1 ? ? ? ? 1 1 0 1 1 1
- - 0 - - - - 0 1 0 1 1 2 1 1 1 1 1 1 2 0 1 1 0 1 1 1
1 0 0 - - - - 0 1 0 1 1 2 2 1 0 1 1 ? 2 0 0 1 0 1 2 1
1 0 0 - - - - 0 1 ? 1 1 2 2 1 0 1 ? ? ? ? 1 1 1 1 2 1
- - 0 - - - - 0 1 ? 1 1 1 1 1 ? ? ? ? ? ? 1 1 0 1 1 1
0 0 0 - - - - 0 1 ? 1 1 2 2 1 0 1 ? ? ? ? 1 1 0 1 1 1
APPENDIX 4
NEW SYSTEMATICS
Revised taxonomy of Siboglinidae ( =Pogonophora and
Vestimentifera) shown in indented format. Siboglinidae
is defined as the first polychaete, and all its descendants,
to have an gut occluded by expanded endoderm filled
with chemoautotrophic bacteria, a s seen in the holotype
of Riftia pachyptila Jones, 1981a. Monilifera can be
defined based on apomorphy-based system such that it
is the first siboglinid, and all its descendants, to have
rings of chaetae (uncini) in the opisthosoma, as seen in
the holotype of Sclerolinum magchlenae Southward,
1972. Vestimentifera can be defined as the first siboglinid
and all its descendants to have a vestimentum as seen
in the holotype of Riftia pachyptia. Frenulata is defined
as the siboglinid, and all its descendants, to have a midtrunk girdle, as seen in the holotype of Siboglinum
weberi Caullery, 1914. The taxa of generic rank are not
defined here since their monophyly was not investigated.
Siboglinidae
Monilifera
Sclemlinum
Vestimentifera
Alaysia, Amvestia, Escarpia, Lamellibrachia,
Oasisia, Ridgeia, Riftia, Tevnia
Frenulata
Birstenia, Choanophorus, Crassibrachia, Cyclobrachia, Diplobrachia, Galathealinum, Heptabrachia, Lamellisabella, Nereilinum, Oligobrachia,
Polybrachia, Siboglinum, Siboglinoides, Siphonobrachia, Spimbrachia, Unibrachium, Zenkevitchiana