JOURNAL OF CRUSTACEAN BIOLOGY, 23(3): 644–661, 2003
PROPOSED NEW STANDARDIZED ANATOMICAL TERMINOLOGY
FOR THE TANAIDACEA (PERACARIDA)
Kim Larsen
Department of Oceanography, Texas A. and M. University, Box 3146, College Station,
Texas 77843-3146, U.S.A. ([email protected])
ABSTRACT
A summary of terminologies and nomenclature currently or previously employed to describe
tanaidacean appendages and somites are presented together with a proposed new standardized
terminology for the order Tanaidacea. Standardized expressions and nomenclatures are suggested for
all tanaidacean somites, appendages, and their articles, as well as for the orientation of tanaidacean
appendages.
The lack of consensus in tanaidacean terminology has long been an obstacle for taxonomical and systematics studies. Much of the
present-day confusion in the tanaidacean systematics is caused by this lack of a common
terminology or by authors mixing structural
terms and terms derived from homology with
other crustaceans. For example, identifying
specific characters on ‘‘pereopod II’’ is bound
to lead to disaster if the observer is not aware
that by ‘‘pereopod II’’ many authors actually
mean the ‘‘first walking leg.’’ This is just the
most obvious problem among a host of inconsistencies within the tanaidacean terminology
and, particularly, within the nomenclature
(Table 1).
A number of papers have dealt with tanaidacean terminology and nomenclature (Lang,
1953a; Wolff, 1956; Gardiner, 1975; Sieg,
1977a; Messing, 1981; Holdich and Jones,
1983; Dojiri and Sieg, 1997), but few of them
agree, and they contain many inconsistencies or
even errors. This paper is an attempt to resolve
this subject by reviewing the different terminologies in use.
The relatively less important questions of
spelling and transliteration are not treated in this
report. For additional information about terminology of other crustacean groups, see
McLaughlin (1980).
TERMINOLOGY AND NOMENCLATURE
Cephalothorax versus Carapace
The head and following two somites (thoracomeres) of tanaidaceans are fused to form
a cephalothorax that is covered dorsally by
a heavily calcified carapace. Sieg (1973) used
the term cephalothorax instead of carapace for
all references to this region and adopted the
definition of Zimmer (1927), that the carapace
only covers the posterior part of the cephalothorax (the fused thoracomeres) and not the
head. The definitions of ‘‘carapace’’ proposed
by Stebbing (1893) and others are somewhat
different and perceive the carapace as a lateral
and dorsal shield covering the cephalothorax
(both head and following fused thoracomeres).
Zimmer’s definition is supported by the embryological study of Scholl (1963), although the
exact boundary between the head and somites
cannot be identified. If Zimmer’s definition of
‘‘carapace’’ requires a suture separating the head
from the following thoracomeres, then it is
problematic. Such a suture cannot be identified
in the Tanaidomorpha (the largest tanaidacean
suborder) and only with uncertainty in the other
tanaidacean suborders. To apply two different
terms in the different suborders clearly would be
counterproductive.
Given this information, the term ‘‘cephalothorax’’ would be appropriate when describing
the region, while ‘‘carapace’’ should be applied
when describing external features. In cases of
morphometric analysis, one would get the same
results regardless of usage.
Pereonites and Pleonites
All malacostracans possess eight somites
(thoracomers) between the head and the abdomen, but two of these are fused with the head
and covered by the carapace. The six (or rarely
five) free somites after the cephalothorax are
together called the ‘‘pereon,’’ and ‘‘pereonites’’
individually, in the tanaidacean literature. The
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Table 1. Different terminologies and nomenclatures for tanaidacean appendages.
Bate, 1856
First cephalic
appendage
First or
anterior
antennae
Second cephalic Second or
appendage
external
antennae
Fourth cephalic First
appendage
maxilla
Fifth cephalic
Second
appendage
maxilla
First
Maxilliped
thoracopod
Second
1. Gnathopod
thoracopod
Third
2. Gnathopod
thoracopod
Following
thoracopods
Pereiopods
1–5
G. O. Sars, 1896
Whitelegge, 1901
Hansen, 1913
Tattersall, 1925
Sieg, 1977
Superior
antennae
Upper
antenna
Antennule
Antennule
Antenna 1
Inferior
antennae
Lower
antenna
Antenna
Antenna
Antenna 2
Anterior
maxillae
Posterior
maxillae
Maxilliped
First
Maxillule
maxilla
Second
Maxilla
maxilla
(not mentioned) Maxilliped
(not mentioned)
Maxilla 1
(not mentioned)
Maxilla 2
(not mentioned)
Maxilliped
Cheliped or
First leg
first leg
Second leg,
Second leg
Pereiopod 1,
Fossorial leg
(in Apseudidae),
Ambulatory leg
(in Tanaididae)
Pereiopods 2–6
Legs 3–7
pereonites are part of the thorax, but the
thoracomers are not necessarily pereonites
(McLaughlin, 1980). Unfortunately, this definition has not been followed by all workers on
the Tanaidacea. Some workers have considered
the fused somites covered by the carapace as
being part of the pereon, but those workers have
not even agreed on how many should be
included (Messing, 1981: 98). The next five
somites are termed ‘‘pleonites’’ and together
with a sixth pleonite fused to the telson
(pleotelson), this region is termed the ‘‘pleon’’
(Gardiner, 1975).
While few or no problems exist with the
nomenclature of the pleonites, which are numbered one to five (or less if fusion occurs), major
confusion is encountered with the nomenclature
of the pereonites. Previously, authors have been
numbering the pereonites in several different
ways.
One system, which unfortunately is still in
use, is the nomenclature of Hansen (1913). This
system is derived from the concept that only one
thoracomer is fused to the head (Hansen, 1913:
8), and Hansen therefore numbers the first free
pereonite as number 2. This approach has
caused much confusion over time. Firstly, it
does not follow the crustacean homologies as
there are two fused thoracomeres covered by the
carapace; secondly, the fused thoracomers
should not be counted as pereonites; and thirdly,
Cheliped
Cheliped/
Cheliped/
Pereopod 1
2nd thoracic limb
Pereopod 1
Pereopod 2
3rd thoracic limb
Pereopods 3–7 Thoracic limbs 4–8 Pereopods 2–6
it suffers from not having identifiable structures.
The most serious problem from this system
arises when dealing with the corresponding appendages (see discussion of cheliped and
pereopods).
Tattersall (1925) used a numbering system
based on homologies. Realizing that two
thoracomeres are fused to the head, this author
numbered the first free pereonite as ‘‘thoracomer three.’’ While essentially correct, this
system is also the least used. The failure of this
system to be widespread lies in the desire for
identifiable structures which is not possible, because the first and second thoracomeres cannot
be identified as separate structures.
A third, and probably the most widespread,
system is the one provided by G. O. Sars (1896)
assigning the first free pereonite as number 1
and subsequent pereonites as 2 through 6. The
advantage of this system is apparent when
dealing with appendages, and if we consider
pereonites as ‘‘free thoracomers,’’ this system
also follows the concept of homologies. All
these three nomenclatures result in different
terms for the tanaidacean appendages (see discussion of cheliped and pereopods). The system
of Sars has the most advantages of these different systems: 1) it is the most widely accepted;
2) all structures are easily identifiably, requiring
no prior knowledge of how many somites are
fused and ‘‘hidden’’; and 3) it conforms well to
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both homologies and the suggested nomenclature of the pereopod system of ‘‘first walking
leg ¼ pereopod 1’’ (see discussion of pereopods).
Antennule and Antenna
The terminology of the first cephalic appendages differs mainly because of cultural differences between the Anglo-American and
Continental European traditions for naming.
Anglo-American authors prefer different names
for different appendages, while the Continental
authors seem to prefer different numbering of
different appendages of a common function.
Thus the different terminologies have caused
name conflicts such as ‘‘antennule’’ versus
‘‘antenna I’’ and ‘‘maxillule’’ versus ‘‘maxilla
I.’’ This difference, however, does not seem to
have caused any serious confusion.
Most authors divide the antennule and
antenna into a stout basal part, the ‘‘peduncle,’’
and a slender distal part, the ‘‘flagellum,’’ as in
other peracarids. In species with biramous
antennules, the basal part proximal from the
separation of rami is the ‘‘peduncle.’’ The
biramous part distal to the separation of rami is
termed ‘‘flagellum’’: outer and inner (accessory
flagellum). This is consistent with most other
peracarid terminologies but leads to a number
of problems. Firstly, it fails when applied to
species with uniramous antennae. In most
species of Tanaidomorpha and Neotanaidomorpha, it is not obvious where the flagellum starts,
if it exists at all (Fig. 1). Secondly, there seems
to be no consensus as to which part the common
article of biramous antennules belongs. Some
authors include it in the peduncle (Gardiner,
1973; Sieg; 1986a; Bamber, 1998), some the
flagellum (McSweeny, 1982), and others do not
count it at all (Lang, 1968; Guţu, 1996). To
leave the common article out altogether is
clearly untenable, and, because the word
peduncle means ‘‘stem to which something is
attached,’’ it is here suggested to include this
article in the peduncle (Fig. 1A). One interesting
way to determine the boundary between the
flagellum and peduncle, as suggested by a reviewer, is to look at the ‘‘swimming males’’ of
certain tanaidomorphan taxa. In these males, the
peduncle consists of two stout articles and one
reduced asymmetric article. The flagellum consists of several articles, all with dense ventral
tufts of aesthetascs. The problem is that this
definition is useless when dealing with taxa
where the males are not of the swimming type
and the antennule is radically different. Another
problem is that the peduncle of Tanaidomorpha
and Apseudomorpha will then not be of the
same length.
Regarding the antenna, some authors count
the squama-bearing article (article 2) as the last
peduncle article (Lang, 1968; Sieg et al., 1982;
Viskup and Heard, 1989), and others believe
that the ‘‘peduncle’’ of the antenna goes beyond
the article with the squama (Guţu, 1996;
Bamber, 1998) and apparently use the size of
the articles to decide where they belong. Several
workers on Apseudomorpha (McSweeny, 1982;
Meyer and Heard, 1989) and most on Neotanaidomorpha (Gardiner, 1975; Larsen 1999a)
and Tanaidomorpha (Lang, 1968; Shiino, 1978;
Sieg, 1986a; Larsen, 2002) refrain from using
the term peduncle at all and assign numbers to
the articles. Because peduncle means ‘‘stem’’
and flagellum means ‘‘whip’’, it is unsatisfactory to limit the peduncle to the part proximal to
the squama, when robust articles extend beyond
the squama in many taxa (Fig. 2A). To use size
as the only character seems also to be a dubious
approach, as many species (for example in the
Pagurapseudidae) experience a steady and indistinct decline in article size in the distal
direction (Fig. 2B). There are also no obvious
serially repeating articles in the antennal
flagellum of either Tanaidomorpha or Neotanaidomorpha (Fig. 2C, D). The musculature of
the antennal flagellum articles in those Apseudomorpha that do have an obvious flagellum is
rudimentary, but in those species without
serially repeating articles, there appears to be
no discrete difference in the musculature of
distal/proximal articles. The degree of spination/
setation is also not different in the distal/proximal antennular articles of most tanaidomorphans or neotanaidomorphans (Fig. 2C, D).
In the case of the antenna in general, and in
the tanaidomorphan and neotanaidomorphan
antennule, the best approach seems to be simply
assigning numbers to the articles in a proximaldistal direction. This approach would eliminate
much of the confusion even if it may be a bit
tedious when dealing with taxa with multiarticulated antennae.
Mouthparts
The labrum has only been given one other
term, the ‘‘upper lip’’ (Boesch, 1973), but the
consensus is to use the term labrum (see
discussion of the labium). Băcescu (1987)
named the labrum a ‘‘process on the clypeus.’’
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Fig. 1. Antennule peduncle. A, Apseudomorpha. B, Neotanaidomorpha. C, Tanaidomorpha.
Because clypeus is the region of the head where
the labrum is attached, this is not wrong, but the
labrum is a more precise term for this structure.
The labium has been given several different
terms. ‘‘Paragnath’’ was used by Shiino (1937),
but Shiino switched to the term ‘‘labium’’ in his
later publications. Dojiri and Sieg (1997) and
Guţu and Sieg (1999) also mentioned the term
paragnath, as well as ‘‘hypopharynx,’’ but did
not use those terms in any of their descriptions.
‘‘Lower lip’’ is another term found in the literature (Boesch, 1973). Although this term is just
the English word for labium, the latter must be
preferred because labium has a much higher
representation in the literature.
The palp of the labium has been termed
‘‘palp’’ by most authors (Sieg, 1986; Meyer and
Heard, 1989; Dojiri and Sieg, 1997; Guţu and
Sieg, 1999; Hansknecht et al., 2001), although
a number of other terms have appeared in the
literature: 1) ‘‘Last segment’’ (Guţu, 1975), and
it is indeed the last segment (article) of two of
the labium, but this is not very consistent with
the terminology of other mouthparts; 2) ‘‘anterolateral plate’’ was used by Wolff (1956) but
was not followed by other workers; 3) several
different word combinations ending in ‘‘lobes’’
have been applied to this structure (Wolff, 1956;
Lang, 1968, Gardiner, 1973; Shiino, 1978;
Guţu, 1998; Larsen, 1999b). To use the term
‘‘lobes’’ is, however, unfortunate because this is
also the term used for the circular basal
structures of the labium (Lang, 1968; Shiino,
1965; Sieg, 1980; Larsen, 2000). Because
the palp is articulated from the labium in
the Apseudomorpha and Neotanaidomorpha
(although different degrees of fusion may
obscure this, particularly within the Neotanai-
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Fig. 2. Antenna peduncle. A, Carpoapseudes. B, Pagurapseudes. C, Neotanais. D, Tanaella.
domorpha), ‘‘lobes’’ would be erroneous. In the
Tanaidomorpha, a structure can sometimes be
present on the lateral corners and has been
termed ‘‘processes’’ because no articulation can
be identified. It is possible that these ‘‘labium
processes’’ are rudiments of the palp but could
also be secondarily evolved. The solution here
would be to call this distal structure ‘‘palp’’
when articulation exists and ‘‘process’’ when
no articulation is found, and reserve the term
‘‘lobes’’ for the basal rounded structures
(Fig. 3).
The mandibles seem to have been spared
from terminological confusion, although Dojiri
and Sieg (1997) used the term ‘‘pars molaris’’
for the molar and ‘‘pars incisiva’’ for the incisor.
The maxillule and maxilla have been termed
‘‘Maxilla 1’’ and ‘‘Maxilla 2’’ (Sieg, 1972 and
others) or ‘‘Anterior maxillae’’ and ‘‘Posterior
maxillae’’ (G. O. Sars, 1896). This appears not
to have caused any major confusion, and consensus is now moving towards the opinion of
Bate (1856), who used the terms maxillule and
maxilla. The different subdivisions of the
maxilla, however, have had several terms applied. The maxilla of Neotanaidomorpha and
Apseudomorpha consists of a movable (outer)
endite, divided into two lobes, and a fixed
(inner) endite, also divided into two lobes
(Guţu, 1996). ‘‘Inner’’ here represents the side
facing the median plane of the animal (Figs. 4
and 12). Hansknecht et al. (2002) used the term
‘‘inner endite’’ instead of ‘‘fixed endite,’’ and
Larsen (1999b) used ‘‘inner process’’ instead of
‘‘inner endite.’’ Gamo (1984) used the term
‘‘distal portion’’ for the outer lobe of the fixed
endite. Lang (1968) used the term ‘‘fixed
endite’’ solely for the outer lobe of the fixed
endite. Lang (1968) did not name the part of the
maxilla that is generally named as the inner
lobe, and described the setal row on this region
as a ‘‘rostral row of setae.’’ This was followed
by a number of authors (Gardiner, 1973; Sieg,
1986a; Viskup and Heard, 1989), although these
authors used the term ‘‘medial row’’ instead of
‘‘rostral row.’’ As this region is clearly a distinct
part of the fixed endite, it is here suggested that
it be called ‘‘inner lobe of fixed endite’’ and that
the row of setae on it be described as ‘‘being on
the inner lobe of the fixed endite’’ instead of just
calling it medial or rostral. The maxilla of
Tanaidomorpha is reduced to an almost featureless ovoid structure and has thus been spared
terminological disputes.
The maxilliped is the first thoracic appendage
even though the somite from which it originates
is fused with the head. Most authors agree thus
far, and the term maxilliped is not under dispute.
However, associated with the maxilliped is an
additional structure, the epignath, the affinity of
which has been under dispute. The epignath has
a ventilatory function in tanaidaceans (Siewing,
1951; Johnson and Attramadal, 1982a, 1982b)
and is believed by some to be the original
exopod of the maxilliped because of a clear
muscle connection, although no articulation has
been demonstrated (Claus, 1884; Dennell, 1937;
Sieg, 1984). An affinity with the cheliped has
also been suggested (Lauterbach, 1970), while
some authors consider it an independent appendage (Blanc, 1884; Siewing, 1953, 1957).
While the authors contest the affinity, only
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649
Fig. 3. Labium, palp, lobes and processes. A, Apseudomorpha. B, Neotanaidomorpha. C, Tanaidomorpha (Bathytanais). D,
Tanaidomorpha (Leptochelia).
Barnard (1935) uses a different term, ‘‘epipod,’’
for this structure. The term epignath can thus be
applied without confusion.
Cheliped and Pereopods
The confusion in the nomenclature of the
pereonites as described above results in a similar
confusion regarding nomenclature of the ap-
pendages attached to them. Several authors have
given different versions of appendage numbering in tanaids as seen in Table 1, and Messing
(1981) has given a good review into the background of many of the terms.
Following the system by Tattersall (1925),
the cheliped is ‘‘thoracopod II,’’ and the first
walking leg will be ‘‘thoracopod 3.’’ While it is
Fig. 4. A, Maxilla, endites and lobes (Apseudomorpha/Neotanaidomorpha). B, Maxilla (Tanaidomorpha).
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true to the concept of homologies that the
cheliped is a thoracopod, the problem with this
system is that nonspecialists will automatically
search for the ‘‘missing’’ thoracopods (Fig. 5A)
as chelipeds and maxillipeds rarely are termed
thoracopods.
According to Hansen (1913) the cheliped is
‘‘thoracopod I,’’ and the first walking leg thus
becomes ‘‘pereopod 2’’ (Fig. 5B). Hansen was
not alone with this misconception, as Whitelegge (1901) had applied the same nomenclature
but called the cheliped the ‘‘first leg’’ and
numbered the pereopods as 2–7. Lang (1953a)
realized that the cheliped is the second thoracopod but retained the terms ‘‘cheliped’’ and
‘‘pereopod 2.’’ He (Lang, 1953a: 342) presented
a table of terms previously used for the first
three ‘‘legs’’ [sic]. This table is, however,
confusing, because Lang used terms for the
first four thoracopods in his three ‘‘leg’’
columns. Lang was followed by Wolff, although he (Wolff, 1956: 189) suggested that the
cheliped was the ‘‘second leg’’ as well as the
‘‘first pereopod,’’ because he considered the first
thoracic somite (fused to the head and bearing
the maxilliped) not to be part of the pereon
while the second thoracic somite (also fused
to the head, bearing the chelipeds) was. The
confusion is apparent with this system, and
nonspecialists have little chance of using
it correctly. If we follow the definition of
McLaughlin (1980), the somites that are fused
to the head are thoracomers, not pereonites, and
thus the cheliped should never be termed the
‘‘first pereopod.’’
The cheliped was also termed ‘‘first gnathopod’’ by Bate (1856), and he also termed the
first walking leg ‘‘second gnathopod,’’ following amphipod terminology (Fig. 5C). Bate
argued that this is the proper term because this
limb is rarely used for walking (which is correct
but only for some taxa). Bate also used
a nomenclature where the second free pereonite
is numbered 3, while the leg it is carrying is
numbered pereopod 1, which makes the confusion complete. This system was followed by
Norman and Stebbing (1886). Barnard (1935)
mixed the systems and termed the cheliped
‘‘gnathopod 1,’’ while the first walking leg was
‘‘pereopod 2.’’
G. O. Sars (1896) first used the terms
‘‘cheliped’’ for the cheliped and ‘‘pereopod 1’’
for the first walking leg, although he was not
consistent. He (G. O. Sars 1896: 1–5) called the
cheliped the ‘‘first leg’’ and the first walking leg
Fig. 5. Nomenclatures of the anterior thoracopods. A,
According to Tattersall (1925). B, According to Hansen
(1913). C, According to Bate (1856). D, According to Sieg
(1977a).
the ‘‘second leg,’’ while later in the same publication (G. O. Sars, 1896: 6–44) the cheliped
was then called ‘‘cheliped’’ and the first walking
leg was called the ‘‘fossorial leg’’ in the
Apseudidae and ‘‘first ambulatory leg’’ in the
Tanaididae. Sieg (1977a) also used the terms
‘‘cheliped’’ for the cheliped and ‘‘pereopod 1’’
for the first walking leg, whether it is used for
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walking or not, and at least he was consistent
(Fig. 5D).
The existence of such different nomenclatures is clearly confusing and untenable.
Furthermore, any student or worker not familiar
with the history of Tanaidacea literature will be
confused by a numbering system describing the
first walking leg as anything but number 1. For
simplicity alone, the nomenclature of pereopods
1 through 6 seems to be causing the least confusion. Furthermore, there seem to be much
confusion as to what ‘‘pereopod’’ means. Bate
(1856: 27) and Messing (1981: 98), stated that
the word means ‘‘walking leg’’ (Greek: pereon ¼
‘‘to walk about’’ þ pod ¼ foot). Wolff (1956)
stated that Bate was incorrect and that pereon
means crossing over (Greek: pereion ¼ ‘‘to
bring to the other side’’ or ‘‘to cross to the other
side’’). One reviewer stated that it actually
means transport. According to my dictionary
(Pring, 1982), Wolff is correct. However, no
matter who is correct in this translation issue, all
translations indicate function and not homology.
If this is correct, then it would be misleading to
apply the term pereopod to the cheliped and
maxilliped, as also would be the conclusion if
we follow the definition of pereon by McLaughlin (1980).
651
same structure (Fig. 6C). Because this structure
is a sclerite of the carapace (Larsen 2001), the
name sclerite is appropriate.
To further complicate the issue, a few taxa
(Nesotanais, Paranarthrura) within the Tanaidomorpha have a subdivision of the cheliped
basis (Fig. 6D). This ‘‘basis subdivision’’ was
first described by Hansen (1913) and later by
Lang (1971), who considered the subdivision to
be reflecting a fusion of the coxa and the basis
and thus used the term ‘‘coxa’’ for the proximal
subdivision of the cheliped basis. This is
entirely possible but unlikely, because no other
tanaidomorphans have a coxa (see above).
Shiino (1968), however, thought it was a division of the basis and ischium. This is also
a possibility but equally unlikely, because no
other tanaidomorphans have even a vestigial
cheliped ischium. Shiino (1968) used the term
‘‘basis’’ for the proximal subdivision of the
cheliped basis. Sieg (1984) was more uncertain
about the origin of this structure and introduced
the term ‘‘pseudocoxa.’’ Whether this structure
is indeed a coxa, a basis, an ischium, or a totally
unrelated structure remains to be determined,
and until then, the term pseudocoxa is recommended for this structure.
Articles of the Cheliped and Pereopods
Cheliped Ischium, Merus, Carpus, Propodus,
and Fixed Finger
The basic division of articles in the tanaidacean appendage is as follows: Coxa (if any),
basis, ischium (if any), merus, carpus, propodus,
and dactylus. However, not even this division is
without controversy. Only in some taxa within
the Apseudomorpha (Fig. 6A) is the cheliped
attached to the cephalothorax via a small true
coxa (Sieg, 1984; Guţu and Sieg, 1999). An
analogous structure found in the Neotanaidomorpha (Fig. 6B) has also been termed ‘‘coxa’’
(Hansen, 1913; Gardiner, 1975; Messing,
1977), but this structure is not homologous
with the coxa and, rather, is derived from the
cephalothorax and thus not an article of the
appendage itself (Lauterbach, 1970). This neotanaidomorphan structure is homologous with
the sidepiece in the Tanaidomorpha (Lauterbach, 1970). Sieg (1976a) called this structure
‘‘coxa,’’ but in 1984 and later publications, Sieg
used the term ‘‘sidepiece’’ for this structure in
the Tanaidomorpha, while retaining the term
coxa for the neotanaidomorphan equivalent.
Still later, the terms ‘‘triangular plate’’ (Larsen
and Wilson, 1998) and ‘‘sclerite’’ (Larsen,
2001) appeared in the literature describing the
Most Tanaidacea do not have a cheliped
ischium. Apart from the potential ischium-basis
described by Shiino (1968) and mentioned
above, we only find a vestigial ischium within
the Neotanaidomorpha (Gardiner, 1975; Sieg,
1984). This ischium (Fig. 6B) consists of an
incomplete ring surrounded by an articulated
membrane and frequently partly covered by the
basis (Larsen, 1999a).
Most authors accept that the article after the
cheliped basis is the merus (Lang, 1968;
Gardiner, 1975; Sieg, 1986a). Yet Hansen
(1913: 8) was of the opinion that this article
was the ischium, and that the following article
was a fusion of the carpus and merus. Monod
(1935: 453) was of the opinion that the carpus
was a fusion of the ischium and a preischium. It
is apparent that neither of these authors was
aware of the vestigial ischium found in the
Neotanaidomorpha, which clearly demonstrates
that the carpus and merus are two separate articles not including the ischium.
The propodus of the tanaidacean cheliped is
equipped with a process termed the ‘‘fixed
finger’’ of the chelae. This structure is
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JOURNAL OF CRUSTACEAN BIOLOGY, VOL. 23, NO. 3, 2003
Fig. 6. The cheliped coxa, sclerite, pseudocoxa, and ischium. A, Apseudomorpha. B, Neotanaidomorpha. C,
Tanaidomorpha (Paratanais). D, Tanaidomorpha (Paranarthrura).
frequently described separately from the propodus but is rarely perceived as an independent
article. Exceptions to this were Hansen (1925:
115) and Monod (1935: 435), who described the
propodus (inclusive the fixed finger) as the
‘‘carpus-propodus.’’
Terminal Structure of the Pereopod Dactylus
The shape of the pereopod dactylus is
important in making family designations for
many taxa (Sieg, 1984; Larsen and Wilson,
2002). Unfortunately, many different terms
have been used for the terminal structure of
the dactylus, including nail (Norman and Stebbing, 1886), claw (Hansen, 1913), hook (Shiino,
1965), terminal spine (Sieg, 1977a), dactyloclaw (Băcescu, 1980), terminal seta (Larsen
and Rayment, 2002), and unguis (Boesch,
1973)(Fig. 7). This terminal dactylus structure
is actually just the sclerotized tip of the dactylus
and not an article in itself. The term ‘‘claw’’ is
thus justified, in a sense, because this structure
is analogous with the mammalian analogues.
The term claw is, however, potentially confusing, because this term is also used to describe
the claw-shaped combination of the dactylus/
unguis found on the last three pairs of
pereopods in several tanaidacean taxa, as described in Pseudoleptochelia (Sieg, 1976b),
Heterotanaoides (Sieg, 1977b), Nototanais
(Sieg, 1980), Paratanais (Sieg, 1981), Tanaissus (Jones and Holdich, 1983), Leptochelia
(Larsen and Rayment, 2002), and others.
To name this structure a ‘‘spine’’ may also be
justified if one chooses to consider this as
a pointed extension of the dactylus cuticle, but
this is more dubious, because it is actually only
a thickening of the cuticle rather than an
extension.
The term ‘‘terminal seta’’ appeared in Larsen
and Rayment (2002), after a reviewer commented that ‘‘since Watling (1989) had established the definition of setae as being articulated
from the cuticle, this structure should be termed
‘seta’ and not ‘spine’ as it displays an articulation.’’ The term was used in a number of
following papers (Larsen, 2002; Larsen and
Wilson, 2002), which is unfortunate because
this structure has nothing to do with a seta, and
the suture between it and the dactylus proper is
not a true articulation. We may hope that this
term will not be used in the future.
Another term for this structure is unguis
(Boesch, 1973; Jones and Holdich, 1983), which
actually means nail or claw (Latin). This term is
used for the homologous structure in isopods
(Wilson, 1989) and insects; and as it cannot be
confused, it must be the preferred term.
A homologous structure is sometimes found
on the tips of the cheliped dactylus and fixed
LARSEN: STANDARDIZED TANAIDACEAN TERMINOLOGY
653
Fig. 7. Pereopod unguis. A, Not fused with dactylus to form a ‘‘claw’’ (Tanaella). B, Fused with dactylus to form a ‘‘claw’’
(Paratanais).
finger. The one on the fixed finger was called
a ‘‘tooth’’ by Shiino (1937). There really is no
need for a different term for this structure, because it is just a thickening of the cuticle and
thus homologous with the unguis of the
pereopods. Furthermore, the term tooth is
unfortunate because it can be confused with
the processes and denticles on the margin of the
fixed finger that are sometimes called ‘‘teeth.’’
The Proximal Uropodal and Pleopodal Article:
Protopod, Peduncle, Sympodite, Basis,
Basipodite, or Basal Article
The proximal article of the uropod that
connects the uropod to the pleotelson also has
several terms in the literature. ‘‘Basis’’ is a term
used by many authors (Lang, 1968; Bird and
Holdich, 1984; Ishimaru, 1985; Bamber, 1990).
Because ‘‘basis’’ means foundation, the term is
literally correct. However, it remains to be shown
that this article really is derived from the basis. It
might be a coxa or a fused coxa/basis. The
question also arises whether such terms should be
applied to nonleg appendages at all; because coxa
means ‘‘hip,’’ it relates to ‘‘legs.’’ The fact that
this word has been applied to both the maxilliped
and the cheliped is a different topic.
The term ‘‘protopodite’’ was introduced by
Shiino (1963), although he used peduncle in
earlier publications, and ‘‘protopod’’ was used
by Gardiner (1973) to alleviate this problem by
considering this article to be, at least, either
a coxa, a basis, or a fused coxa and basis. Protopod (¼ coxa þ basis) was therefore considered
a more accurate term. However, this is homologous with standard crustacean terminology (as
one reviewer pointed out) only if it really is
a fusion of the coxa and basis. There is no way
to tell, so this term does not solve the problem.
Dojiri and Sieg (1997) introduced the term
‘‘sympodite’’ without justification. In a later
review of the Tanaidacea (Guţu and Sieg,
1999), this term appeared again but was not
consistently applied throughout that paper. Guţu
does not seem to use the term in any later papers
either.
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JOURNAL OF CRUSTACEAN BIOLOGY, VOL. 23, NO. 3, 2003
Fig. 8. Setae and spines. A, Simple seta. B, Pinnate/pappose/plumose/sensory/setulose/broom seta. C, Serrated seta. D,
Feather/plumose seta. E, Bipinnate/douple sided setulose seta. F, Pinnate/single sided setulated seta. G, Spiniform seta. H,
Bifurcate seta. I, Leaf-shaped seta. J, Short flat seta. K, Coupling hook. L, Circumplumose seta. M, Spines.
Fig. 9. Mancas. A, Manca I hatchling, after Bückle-Ramirez (1965). B, Manca II. C, Manca III. D, Juvenile.
LARSEN: STANDARDIZED TANAIDACEAN TERMINOLOGY
655
Fig. 10. Appendage orientation. A, Ventral/dorsal for the animal in situ. B, Ventral/dorsal for the cheliped in situ. C,
Ventral/dorsal for the pereopods in situ. D, The orientation of inner and outer relative to ventral and dorsal.
‘‘Peduncle’’ was used by a number of authors
(Wolff, 1956; Lang, 1957; Müller, 1992; Edgar,
1997) as an analog to the part of the antennule,
proximal to the separation of rami. This term
may be applied but not without conflict. On
biramous uropods, it is easy to distinguish between this article and other exo-endopod
articles, but in uniramous uropods, it is not so
obvious and we end up with the same problem
as for the antenna.
Because all tanaids have only one article
proximal from the separation of the rami, it is
here proposed to call this article the ‘‘basal
article,’’ following the procedure for the antenna. Most of this paragraph applies to the
proximal article of the pleopods as well. In
case of uniramous pleopods (and uropods), it is
generally accepted that the endopod is retained,
and this term thus should be applied.
Setae, Spines, and Cuticular Scales
The long-standing discussion of what are
considered spines and what are setae has caused
significant damage to tanaidacean systematics
as well as to the systematics of most other
crustaceans. It is obvious that some tanaid
workers (Sieg, 1986a; Guţu 1996; Bird, 1999)
considered a thick seta as being a ‘‘spine,’’
while others did not (Viskup and Heard, 1989;
Larsen 1999a; Bamber, 2000; Hansknecht
et al., 2001) and still others were not consistent
in their usage (Lang, 1968). Sieg (1986a, b)
claimed that the presence of ‘‘spines’’ on certain
articles of certain appendages was of major
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JOURNAL OF CRUSTACEAN BIOLOGY, VOL. 23, NO. 3, 2003
Fig. 11. Application of terms for the pereopod orientation. A, Appendage orientation in situ according to the system of
Sieg, 1977a, with the terms rostral/caudal applied. B, Appendage orientation in situ as seen in a tube-dwelling tanaidacean,
with the terms inner/outer applied and how these conflict with the system of Sieg, 1977a.
phylogenetic value and used this character to
separate families. If a character is important
systematically, then there must be agreement on
its terminology or the character will be rendered
useless. It is therefore easy to understand how
the systematics has become unclear if the
workers did not agree on how to define
a ‘‘spine.’’
The issue is still debated, but there is a trend
towards accepting the definitions based on
homology put forward by Watling (1989). Setae
are thus defined as elongated structures of rather
variable shape that extend from a point under
the cuticle and have innervation and articulation. Spines are extensions of the cuticle itself
forming pointed structures. Spines are longer
than wide at the base and are not innervated or
articulated. Scales are cuticular projections
without innervation and are broader at the base
than long.
To further complicate this issue, it has been
observed that in larger (older?) specimens of
Leptochelia, setae can become fused with the
cuticle and lose their articulation (R. Heard,
LARSEN: STANDARDIZED TANAIDACEAN TERMINOLOGY
Fig. 12. The orientation of the mouthparts (generalized
tanaid) seen from below.
personal communication). Whether this loss
includes innervation is yet to be determined.
The Tanaidacea display a rich variety of more
or less specialized setae, and it would waste
space here to describe them all or to mention all
the different names that have been applied to
them. A short selection of the most common and
important types are found in Fig. 8 with the
most commonly used terms underlined in the
caption. There is generally no need to standardize the many different descriptive terms authors
have applied to setae. Although the terms
describing specialized setae are not identical,
they are usually descriptive enough to avoid
misunderstanding.
Mancas
The manca stages have also been subjected to
several different nomenclatures. Lang (1953b)
used the term ‘‘manca I’’ for a free-living manca
but omitted any remarks on the stage found only
within the female marsupium. Bückle-Ramirez
(1965), however, used the term ‘‘manca I’’ (Fig.
9A) for the newly hatched embryo, and this was
followed by Sieg (1972). ‘‘Manca II’’ (Fig. 9B)
was the term used for the individual newly
released from the marsupium (Bückle-Ramirez,
1965). Messing (1981) observed that there is no
ecdysis between these ‘‘manca I’’ and ‘‘manca
II’’ and suggested that the manca I is better
termed ‘‘lecithotrophic hatchling’’ or ‘‘early
stage’’ of the ‘‘manca I’’ and that the newly
released individual is really the manca I. The
657
difference between these two stages is so
obvious that they must be given two different
terms (ecdysis or not). It is clearly a problem to
apply two different names without an ecdysis,
but to apply the same term to these different
forms would be an even bigger problem.
Because both types have differentiated chelipeds and pereopods (Fig. 9A, B), it is hardly
a larva in the sense of a nauplius, and this term
should not be applied to any of these forms. The
terminology and nomenclature of Bückle-Ramirez (1965) are thus workable, but I here
propose the application of the suffix ‘‘hatchling’’ to the term ‘‘manca I,’’ while retaining the
term ‘‘manca II’’ for the following stage. The
term would be ‘‘manca I hatchling,’’ and this
should eliminate most of the confusion. The
manca II can then be defined as the newly
released manca which does not yet possess
pleopods, any traces of pereopod 6, and only
a very reduced pereonite 6 of the same size as
a pleonite. Manca III, on the contrary, does possess a fully developed pereonite 6 and a vestigal
pereopod 6, but no pleopods. Juveniles have
a fully developed pereopod 6 and pleopods, but
these are vestigal and without setation. Note that
most adult female deep-sea species lack pleopods and some possess rudimentary pleopods,
but these usually do have some kind of setation.
Orientation of Tanaidacean Appendage
The terms ‘‘sternal’’ and ‘‘tergal’’ were originally synonymous with ‘‘ventral’’ and ‘‘dorsal,’’ and were intended to identify the margins
of the chelipeds and pereopods as oriented on
a live animal (Sieg, 1977a; Dojiri and Sieg,
1997). They are used extensively in recent
tanaid literature. However, while Sieg’s application of sternal/tergal correctly correspond to
ventral/dorsal for the cheliped, the opposite
holds true for the pereopods (Fig. 10). Therefore, to use the terms tergal/sternal as synonymous with dorsal and ventral in this situation
would be erroneous and confusing (Larsen and
Rayment, 2002). It is proposed that the terms
sternal and tergal be abandoned when describing the different margins of the tanaidacean
appendage and that, instead, the terms dorsal/
ventral should be applied in the arrangement
shown in Figs. 10B and 10C. This system
would remain stable because this is the
orientation in which all tanaidacean thoracopods
are held in situ.
The terms ‘‘rostral’’ and ‘‘caudal’’ were
employed as synonyms to anterior and posterior
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JOURNAL OF CRUSTACEAN BIOLOGY, VOL. 23, NO. 3, 2003
Table 2. Proposed standardized terminology in anterior to posterior direction.
Origin
Proposed standardized name
Carput
Antennule
Carput
Carput
Carput
Carput
Carput
Carput
Carput
Antenna
Cephalothorax
Carapace
Labrum
Mandibles
Maxillule
Maxilla
Carput
Thorax
Thorax
Thorax
Labium
Maxilliped
Epignath
Cheliped
Subdivision
Peduncle (including common article) and flagellum (in Apseudomorpha),
inner and outer rami. Article number (in Neotanaidomorpha
and Tanaidomorpha)
Article number, inner rami, squama (in Apseudomorpha)
Head, thoracomer 1, thoracomer 2
Occasionally divided into separate plates, covering the entire cephalothorax
Incisor, lacinia mobilis, setal row, molar, palp
Inner endite, outer endite, palp, terminal spiniform setae
Inner and outer lobe of movable endite, inner and outer endite of
fixed endite (in Apseudomorpha and Neotanaidomorpha)
Palp, lobes, processes
Coxa, basis, endites, palp
Lobes, terminal seta
True coxa (Apseudomorpha), pseudocoxa (Tanaidomorpha),
sclerite (Neotanaidomorpha and Tanaidomorpha), basis, ischium
(Neotanaidomorpha), merus, carpus, propodus, fixed finger, dactylus
Thorax Pereonites 1—as many as are present
Thorax Pereopods 1—as many as are present Coxa, basis, ischium, merus, carpus, propodus, dactylus, unguis
Abdomen Pleonites 1—as many as are present
Abdomen Pleopods 1—as many as are present Basal article, endopod, exopod
Abdomen Pleotelson
Abdomen Uropod
Basal article, endopod, exopod
N/A
Appendix orientation
Ventral/dorsal, inner/outer, proximal/distal
sides on the cheliped and pereopods, assuming
that the pereopods were held straight out from
the body (Sieg, 1977a). It is informative to know
which sides of the chelipeds face outwards, but
the use of the terms ‘‘inner’’ and ‘‘outer’’ surface
should be used, because the chelipeds are much
more anteriorly directed than perpendicular to
the body. For the pereopods, the situation is
more complicated. The old system (Sieg, 1977a;
Dojiri and Sieg, 1997) assumes that all pereopods are held in the same orientation (see Fig.
11A). However, most often the three anterior
pairs of pereopods are held facing anteriorly,
while the three posterior pairs are held facing
posteriorly, particularly in tube-dwelling taxa
(see Fig. 11B). Thus, the inner and outer
surfaces of the posterior pairs are reversed
relative to the side of the anterior pairs. Because
the side of the limb facing outwards shares
characters (in armament) with that side of the
other limbs facing outwards, regardless of which
side is facing anterior (if held perpendicular to
the body), the system of Sieg (1977a) is not
optimal. To overcome this problem, it is here
proposed to apply, by convention, the terms
‘‘inner’’ and ‘‘outer’’ in the manner shown in
Fig. 10D as modified from Sieg (1977a).
For the mouthparts, a similar system is
proposed. All the mouthparts are held in
a ventral/dorsal manner in situ, and the paired
mouthparts always face each other on the
‘‘inner’’ side and are anteriorly directed (Fig.
12). One is never in doubt about the orientation
of the mouthparts. The only modification is that
the labrum is as much ventrally as anteriorly
directed, but this should cause little confusion.
Articles, Joints, and Segments
Several authors (G. O. Sars, 1896; Shiino,
1952) have used the term ‘‘segment’’ instead of
‘‘article,’’ and sometimes this term is used
instead of ‘‘somite.’’ This seems not to have
caused any confusion in the tanaidacean
literature. However, Hansen (1913), Shiino
(1937, 1951), and Sieg (1981) used the term
‘‘joints’’ instead of article, and this term may be
confused with the actual joints (or articulations)
between the articles, which was not what any
author intended. This synonymy of joints and
articles is undesirable. The consensus seems to
be moving towards using the term ‘‘article’’ for
the individual units of the tanaidacean appendage (Guţu, 1972; Bird and Holdich, 1984;
Bamber, 1990; Larsen 1999a).
DISCUSSION
A common terminology is essential for
understanding the homologies necessary for
conducting any phylogenetic analysis. Therefore, this suggested terminology is based mainly
LARSEN: STANDARDIZED TANAIDACEAN TERMINOLOGY
on homology. A standardized terminology is
proposed in Table 2 for all tanaidacean somites,
appendages, and their articles, as well as
orientations.
It is not expected that every worker on the
Tanaidacea will uncritically adopt this proposed
terminology and nomenclature. Rather, the
object of this paper is to clarify the terminology
and to identify the problem that several different
terminologies and nomenclatures have been
employed. If tanaid specialists could be inspired
to include a section in their publications about
which terminology they adhere to, much
confusion could be avoided. Particularly, those
workers new to the fascinating group of
Tanaidacea would benefit tremendously from
such a change in behavior.
ACKNOWLEDGEMENTS
The funding for this project was provided by the BP
Deep-Sea Biodiversity Fellowship, hosted by the Department of Oceanography, Texas A. and M. University. Part of
the work took place at the Gulf Coast Research Laboratory,
and my thanks are extended to this institution. I am grateful
for critical reading of the manuscript by Dr. Fain Hubbard
and thankful to several colleagues for productive (and
sometimes heated) discussions on the subject.
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RECEIVED: 10 September 2002.
ACCEPTED: 20 January 2003.