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J. Moll. Stud. (2000), 66, 99–117
© The Malacological Society of London 2000
SPECIES DISCRIMINATION AMONG PELAGIC
HETEROPODS: RESOLUTION OF THE PTEROTRACHEA
HIPPOCAMPUS—P. MINUTA PROBLEM
ROGER R. SEAPY
Department of Biological Science, California State University, Fullerton, CA 92834-6850
(Received 12 June 1997; accepted 21 May 1999)
ABSTRACT
Four species of Pterotrachea are currently recognized,
two of which (P. hippocampus Philippi, 1836, and P.
minuta Bonnevie, 1920) have very similar morphologies. These two species have been distinguished
mainly on the basis of eye and visceral nucleus
shapes; the former with wide, triangular eyes and a
short, broad nucleus, and the latter with narrower, triangular eyes and a taller, more slender nucleus.
Quantitative and qualitative morphological data were
obtained from specimens of P. hippocampus and P.
minuta collected during two oceanographic sampling
programs in the North Atlantic Ocean. Comparisons
of eye and visceral nucleus shapes (represented by
their length to width and length to retinal width ratios,
respectively), plotted against body length showed
linear decreases, with no justification for the recognition of two separate species. Examination of eye
shape across a wide range of body sizes showed that
the width of the retina increases disproportionately
with body growth (by elongation and medial upturning) beginning at a length of about 21–22 mm. As a
result, the overall appearance of the eye at this body
size changes such that smaller animals (less than
21–22 mm) have eyes corresponding with those of P.
minuta, while the eyes of individuals larger than this
body length match those of P. hippocampus. Several
authors have distinguished females of the two species
by the presence (P. hippocampus) or absence (P. minuta) of cuticular spines anterior to the eyes. Examination of female specimens showed that those less than
about 30 mm lacked these spines, while those above
this size possessed them. Thus, cuticular spines represent a secondary female sexual characteristic.
Other morphological features that have been used by
previous authors to distinguish the two species were
examined and rejected. Because P. hippocampus was
described prior to P. minuta, it is herein regarded as
the senior synonym of P. minuta.
INTRODUCTION
In 1920 Bonnevie published a taxonomic paper
on the Heteropoda collected during the
Michael Sars North Atlantic Deep-Sea Expedition. In her treatment of the family Pterotracheidae, she characterized three species
of Pterotrachea (P. coronata Forskål, 1775,
P hippocampus Philippi, 1836, and P. scutata
Gegenbaur, 1855) and described a fourth
species (P. minuta) on the basis of a single, male
specimen. I examined the holotype of P. minuta
(Seapy, 1985) and found it to be severely
stretched, with the result that the eyes, visceral
nucleus, swimming fin and fin sucker appeared
to be small relative to the total body length.
These disproportionately small features possibly led Bonnevie to propose the specific epithet, minuta. In her review of taxonomic
features that can be used to separate the different species of Pterotrachea, Bonnevie concluded that the eye and visceral nucleus shape
were the most reliable. She characterized the
eyes and nuclei of P. minuta as intermediate in
appearance between those of P. hippocampus
(with wide, triangular eyes and a short, broad
nucleus) and P. coronata (with narrow, tubular
eyes and an elongate, slender nucleus). Subsequent workers (Tesch, 1949; Okutani, 1957a;
Richter, 1968, 1974; Taylor & Berner, 1970; van
der Spoel, 1972, 1976; Thiriot-Quiévreux, 1973;
Aravindakshan, 1977; Pafort-van Iersel, 1983;
Newman, 1990; van der Spoel, Newman &
Estep, 1997) have used eye and visceral nucleus
shapes as the primary (or only) characters distinguishing P. minuta and P. hippocampus.
In the early 1980s I began working with the
heteropod fauna of Hawaiian waters. Initially,
all four of the described species of Pterotrachea
appeared to be present among the specimens
that I examined. Individuals identified as P.
coronata and P. scutata were distinctive (Seapy,
1985), although the remaining specimens presented a problem; those of intermediate to large
size possessed the morphological features of
P. hippocampus, while small individuals had the
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characteristics of P. minuta. Morphological and
morphometric examination of characters used
by previous authors to distinguish P. minuta
from P. hippocampus showed that there was no
support for the separate identity of P. minuta;
at least from Hawaiian waters.
The question remained whether or not P.
minuta is a valid species outside the Pacific
Ocean. Most species of heteropods have a
circumglobal distribution at tropical and subtropical latitudes, although three atlantids and
four carinarids have Indo-Pacific distributions
and one atlantid is limited to the Atlantic Ocean
(Richter and Seapy, 1999). Hypothetically, then,
P. minuta could be a species whose distribution
is restricted to the Atlantic Ocean, as is the case
of Atlanta fragilis (Richter, 1993). To test this
hypothesis, I examined specimen lots of P.
hippocampus and P. minuta collected from the
central and western North Atlantic Ocean.
MATERIALS AND METHODS
Specimens identified as Pterotrachea hippocampus
and P. minuta were obtained from two oceanographic
studies; the Ocean Acre Project in the western North
Atlantic Ocean off Bermuda (1967–1972) and the
Amsterdam Mid North Atlantic Plankton Expedition
(1980). Among the Ocean Acre station samples, those
used here were collected between January 1971 and
June 1972 with a 10-ft Isaacs and Kidd Midwater
Trawl (IKMT) equipped with a four-chambered
cod-end device to sample discrete depths or depth
ranges (Gibbs, Roper, Brown, & Goodyear, 1971).
All samples were collected within a 1° latitude by 1°
longitude grid centered at 32°N and 64°W. The U.S.
National Museum, Washington D.C., retained most
of the sorted heteropod specimens, although a portion was donated to the Zoological Museum of
Amsterdam. Eight lots of specimens identified as
Pterotrachea hippocampus and P. minuta were loaned
to me by these two institutions (Table 1). Morphological data were obtained from 67 specimens.
Plankton tows were taken during the Amsterdam
Mid North Atlantic Plankton Expedition from 11
April to 2 May 1980 at various depths using a combined small (.8 m2) and large (8.0 m2) Rectangular
Midwater Trawl (RMT1 and RMT8 nets, respectively) and a .78 m2 Open Ring Net (RNO). Stations
were located along a transect extending from 25° to
45°N latitude between about 30° and 35°W longitude
(ven der Spoel, 1981). Samples containing specimens
identified by Pafort-van Iersel (1983) as P. hippocampus and P. minuta were loaned to me by the
Zoological Museum of Amsterdam. Morphological
data were taken from 40 of the specimens (Table 2).
Sketches of the right eye (in dorsal view) and the
right side of the visceral nucleus (in lateral view) were
made using a Wild Camera Lucida attached to a Wild
M5 Dissection Microscope. All measurements were
taken through this microscope using a calibrated
ocular micrometer, following procedures described
previously (Seapy, 1985). Visceral nucleus length and
maximal width were determined and the ratio between
the two measurements calculated. Similarly, the
length of the eye (in its long axis) and the width of the
retinal base were measured, and the ratio between
the two calculated.
The condition of specimens examined in this study
was highly variable, ranging from intact and undistorted individuals to collapsed, stretched specimens
and body fragments. This is not unexpected because
pterotracheids are soft-bodied animals that are easily
damaged during net capture (discussed by Seapy,
1985). If animals are alive at the time of preservation,
their bodies invariably contract and shorten. However, if animals are dead when placed in preservative,
no change in body length occurs. Such specimens are
often stretched and damaged to varied degrees
between the time of capture and retrieval of the net.
Thus, body length measurements obtained from preserved specimens often are not representative of the
size of the animal while it was alive. Despite this problem, preserved body lengths are routinely reported in
the literature and the reader is usually unaware of the
inaccuracy or extent of error involved in many of
these measurements.
In my earlier study (Seapy, 1985), I addressed the
problem of variability in body length among preserved
specimens by selecting a series of P. hippocampus that
did not appear to have lengthened or shortened as a
Table 1. Collection data for specimen lots of Pterotrachea hippocampus and P. minuta from Ocean
Acre stations in the North Atlantic Ocean near Bermuda. Abbreviations: ZMA 5 Zoological Museum of
Amsterdam, USNM 5 United States National Museum, Washington, D.C.
Station
Lot No.
Source
Date
11–12M
13–10M
13–12M
13–30B
13–30B
13–30C
13–39M
14—2M
H808
H746
H638
H754
H756
H797
H581
H799
ZMA
USNM
USNM
USNM
USNM
ZMA
USNM
ZMA
15 Jan 71
25 Feb 72
25 Feb 72
1 Mar 72
1 Mar 72
1 Mar 72
3 Mar 72
5 Jun 72
Depth (m)
0–50
0–96
0–105
34
34
34
0–719
0–282
Species
P. minuta
P. minuta
P. minuta
P. hippocampus
P. minuta
P. minuta
P. hippocampus
P. hippocampus
No. Specimens
24
1
11
5
18
5
2
1
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Table 2. Collection data for specimen lots of Pterotrachea hippocampus and P. minuta from stations
occupied by the Amsterdam Mid North Atlantic Plankton Expedition. Latitude and longitude coordinates for stations are rounded to the nearest minute. Station data from van der Spoel (1981). See text
for description of net types.
Station Lot No. Net Type Latitude
Longitude Tow Depth (m) Species
17–2
19–13
19–13
19–19
20–10
20–13
21–19
22–7
22–8
23–2
24–2
24–2
24–2
24–4
24–4
35°319W
35°279W
35°279W
35°189W
31°299W
31°319W
30°399W
29°549W
29°549W
30°009W
29°589W
29°589W
29°589W
29°589W
29°589W
6013
6033
6041
6034
6049
6046
6058
6114
6067
6076
6082
6085
6087
6081
6051
RMT8
RMT8
RMT8
RMT8
RMT8
RNO
RMT8
RMT8
RNO
RMT8
RMT1
RMT8
RMT8
RNO
RNO
41°119N
38°009N
38°009N
37°549N
35°119N
35°139N
33°309N
31°589N
31°589N
30°409N
29°489N
29°489N
29°489N
29°459N
29°459N
330–505
100–200
100–200
50–110
100–200
50–110
105–120
90–200
0–50
505–960
110–205
110–205
110–205
0–50
0–50
P. hippocampus
P. hiippocampus
P. hippocampus
P. hippocampus
P. minuta
P. hippocampus
P. hippocampus
P. hippocampus
P. hippocampus
P. hippocampus
P. minuta
P. minuta
P. minuta
P. hippocampus
P. minuta
No. Specimens
1
3
2
1
3
2
1
6
1
1
3
2
11
1
2
Figure 1. Lens diameter (mm) in relation to total body length (mm) (r 5 1.98; Y 5 .007X 1 .193). Specimens
identified previously as P. hippocampus shown by solid circles; those as P. minuta by open circles.
result of capture damage or preservation, respectively.
I found that body length and lens diameter were positively correlated (r 5 1.96). The resultant regression
equation (Y 5 .008X 1 .164) defined a line of best fit
that enabled me to estimate the body lengths of specimens on the basis of their lens diameters without
regard to their preserved condition.
Among the specimens available in the present
study, I selected 42 individuals that were not noticeably stretched or contracted and measured their body
lengths and lens diameters (Fig. 1). These two variables were strongly correlated (r 5 1.98) and yielded
a line of best fit defined by the regression equation:
Y 5 .007X 1 .193. The transposed equation (X 5
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R.R. SEAPY
142.857Y 2 27.571) was then used to compute body
lengths from the lens diameters for all specimens.
No type material of P. hippocampus exists in
museum collections to my knowledge. However, the
holotype of P. minuta is housed at the Zoologisk
Museum, University of Bergen, Norway (ZMUB
23259). I examined this male specimen in preparation
for my 1985 paper and found that its total body length
(38.8 mm) was shorter than the 47-mm length
reported by Bonnevie (1920). I took a variety of
morphometric measurements from the animal, and
also made a camera-lucida drawing of the right eye.
Using the regression equation above and the measured lens diameter (.33 mm) of the holotype animal,
a body length of 19.6 mm was obtained. The length to
width ratio of the visceral nucleus (3.20) and the eye
length to retinal width ratio (1.67) of the holotype
animal are included below for comparison with specimens examined in the present study.
RESULTS
Bonnevie (1920) described a series of morphological features (summarized in Table 3) to
characterize Pterotrachea hippocampus and P.
minuta. Since the single specimen of P. minuta
available to her was a male, she was not able to
compare any of the secondary female sexual
characteristics seen in the former species with
the latter species. Because Bonnevie and other
authors considered the shapes of the eyes and
visceral nucleus to be the most important taxonomic characters, results for these two structures are presented first. Other differences cited
by Bonnevie and subsequent authors are then
discussed in the order given in Table 3.
Eyes:
The most conservative and distinctive difference between P. hippocampus and P. minuta is
eye morphology. Bonnevie’s characterization is
given in Table 3. Other authors have presented
similar descriptions (Table 4), and several
(Richter, 1974, and Pafort-van Iersel, 1983)
have noted additional differences. Taking these
sources together, the eyes of P. minuta can be
characterized as narrowly triangular, with the
length of the eye exceeding its greatest width.
The narrowness of the eye is due to the presence of a relatively short retina, whose medial
end curves distally but does not reach the base
of the lens (in the long axis of the eye). In
contrast, the eye of P. hippocampus is broadly
triangular, with the length approximately equal
to the width. This eye shape results from a
retina that is longer than that in P. minuta and
which reaches or extends distally past the proxi-
Figure 2. Ratio of eye length to retinal width in relation to body length for individuals identified previously
as P. hippocampus (solid symbols) and P. minuta (open symbols). For specimens less than 46 mm, regression
analysis gave a line of best fit defined by the equation Y 5 2.018X 1 1.948 (r 5 2.94). The mean eye length to
retinal width ratio for individuals greater than 46 mm was 1.12. Body lengths based on lens diameters calculated
using the regression equation from Figure 1. Length to width ratio for P. minuta holotype indicated by ‘1’
symbol. Specimens from Ocean Acre samples shown by triangles; those from North Atlantic Plankton Expedition by circles.
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Table 3. Morphological differences between Pterotrachea hippocampus and P. minuta given by
Bonnevie (1920).
Morphological character
Pterotrachea hippocampus
Pterotrachea minuta
1. Eye shape
broad-based; diameter of retina
somewhat like height of whole
eye
cylindrical in distal part; retina
broader than diameter of
cylindrical part
short and broad; width about
one-half length
nucleus does not reach dorsal
level of body
spindle-shaped; height about
four times greatest width
nucleus rises slightly above
dorsal level of trunk
broad and round, located on
right side of body in front of
visceral nucleus
numerous along base of fin and
on folds of neck in var. punctata;
none in var. apunctata
in two irregular rows anterior to
eyes in females; absent or
rudimentary in males
scattered along lateral muscle
bands of tail; occasionally on
wall of osphradium
unknown (holotype 5 male)
2. Visceral nucleus
a. Shape
b. Dorsal extension
3. Cuticular structures
a. Papilla
b. Spots
c. Spines
d. Tubercles
a few around base of swimming
fin and on ventrum anterior to fin
unknown (holotype 5 male)
lacking from muscle bands of tail
and from wall of osphradium
4. Osphradium
in median dorsal line
somewhat left of median plane
5. Gills
12–15; short; forming a row
posterior to the osphradium wall
11 on holotype specimen; no great
difference in length; forming a
very regular row, with largest gills
on left side
about 23
with median spine far protruding,
and more than 5 small spines
on each side
without a secondary spine at free
end of tooth, although it may be
present as a rudiment
(in var. punctata)
not determined
with median spine shorter than in
P. hippocampus, and 5 or 6 small
spines on each side
with a secondary spine at free end
of tooth
7. Buccal teeth
5 or 6 in two rows; broad-based
5 or 6 in two rows; cone-shaped
with narrow base
8. Male sexual organs
copulatory part of penis consists
penis consists of 3 small leaves
of 2 broad, leaf-like lobes and a
and its glandular organ ends in a
finger-shaped glandular organ
sucker-like plate
(about twice as long as the leaves)
with a sucker-like extension at
the end
6. Radula
a. Number of tooth rows
b. Central teeth
c. Intermediate teeth
mal end of the lens. The eyes of P. minuta are
intermediate in shape between the tubular eyes
of P. coronata and P. scutata and the broadly
triangular eyes of P. hippocampus.
In the present study the ratio of eye length to
retinal width was found to decrease with
increasing body length up to 46 mm (Fig. 2). In
animals larger than about 46 mm, however, the
ratio remained unchanged, averaging 1.12.
These results show that eye shape changes with
growth from narrowly triangular (maximal
length to retinal width ratio of 1.8) to broadly
triangular (minimal ratio of 1.1). Regression
analysis using the ratios obtained from animals
less than 46 mm resulted in a line of best fit
defined by the equation, Y 5 2.018X 1 2.000.
The correlation between the two variables was
strong (r 5 2.94). Clearly, these results provide
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Table 4. Characterization of eye shape in Pterotrachea hippocampus and P. minuta by authors subsequent to Bonnevie (1920).
Authority
Pterotrachea hippocampus
Pterotrachea minuta
Tesch (1949)
broad-based, with large carina-like
retinal part
more like that of P. coronata than
P. hippocampus, but retinal base
somewhat broader and longitudinal
axis shorter
Richter (1968)
width of base nearly matches overall eyes wide (like in P. hippocampus),
eye length; shape somewhat like
but base somewhat narrower in
equilateral triangle
relation to eye length
Taylor and Berner
(1970)
broad-based, with large retinal
area resulting in definite triangular
shape
similar to P. coronata, but retinal base
broader and length of longitudinal
axis of eye shorter
van der Spoel (1972)
broadly triangular
triangular with broad base
Thiriot-Quiévreux
(1973)
triangular with base of retinal
part widened
wide at base, but axial length greater
than in P. hippocampus
Richter (1974)
eyes wide; greatest width (at base)
about matches greatest length
(including the lens); pigmented
covering between base and lens
narrows rapidly toward the lens
eye base narrower than in P.
hippocampus; eye length exceeds
greatest width (but wider than in
P. coronata); pigmented covering
between narrow base and large lens
shaped like a cylinder
van der Spoel (1976)
triangular with broad retina that is
so strongly curved that one top
reaches the lens
triangular with broad base; shape
intermediate between
P. hippocampus and P. coronata
Aravindakshan (1977)
broad-based
shape intermediate between P.
coronata and P. hippocampus;
cylindrical in distal part, but retinal
part broader than cylindrical part
Pafort-van Iersel
(1983)
triangular shape, with broad and
darkly pigmented retina that is so
strongly curved that one end (top)
reaches the lens
shape resembles that of P.
hippocampus, but not as triangular;
retina broad and curved at one side in
the direction of the lens, but does not
reach it
van der Spoel, et al.
(1997)
triangular, with broad retina which
is so strongly curved that one tip
reaches the lens
triangular, with broad base; shape
intermediate between P. coronata and
P. hippocampus
no evidence supporting the existence of the two
different species based on eye shape.
To examine the changes in eye shape that
accompany body growth, sketches were made
of the right eyes in dorsal view from a series of
animals between 7.9 and 51.6 mm body length
(Fig. 3). The eye sketches from the 20.0 mm and
smaller specimens conform to the previous
descriptions of the eyes of P. minuta, while the
eye sketches from the 22,8 mm and larger specimens correspond with the previous descriptions
of the eyes of P. hippocampus. Thus, at a body
length of about 21 to 22 mm, the eye shape
appears to be ‘transformed’ from that of
P. minuta to that of P. hippocampus. This dramatic change in the appearance of the eye can
be attributed to a disproportionate increase in
retinal width relative to eye length during this
period of growth.
Interestingly, the eye shape of the holotype
specimen of P. minuta (Seapy, 1985; Fig. 3E) is
most comparable with that from the 22.8-mm
specimen in Figure 3. This comparison provides
support for my contention that the holotype
animal was much smaller in life; about one-half
of the 47-mm length reported by Bonnevie
(1920).
Visceral nucleus:
Bonnevie (1920; Table 3) and subsequent
authors (Table 5) have characterized the vis-
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Figure 3. Camera lucida sketches of right eyes viewed dorsally. Body length given beneath each sketch was
based on lens diameter, calculated using the regression equation from Figure 1. Asterisks denote males; all
others females, except for 7.9 mm juvenile.
ceral nucleus of Pterotrachea hippocampus as
broad and short (length about two times width)
and that of P. minuta as narrower and more
elongate (length about three times width). In
addition, these authors frequently state that the
nucleus of P. minuta is intermediate in shape
between those of P. hippocampus and P. coronata. The nucleus of the latter species is the most
elongate and slender of the pterotracheids. In
fact, the length to width ratios for P. coronata
from Hawaiian waters ranged from 4.0 to 7.0,
and exceeded those determined for all other
species of Pterotrachea (Seapy, 1985; Fig. 5).
In the present study, the length to width ratio
of the nucleus was found to decrease with
increasing body length (Fig. 4), as defined by
the regression equation: Y 5 2.019X 1 3.136.
On the basis of this plot, there is no evidence
supporting the separate existence of two species.
The negative slope (2.019) of the line of best fit
indicates a disproportionate increase in nucleus
width relative to length, which is probably the
result of gonadal and digestive tissue growth.
In contrast with the strong correlation
between the ratio of eye length to retinal width
and body length (r 5 2.94), the correlation
between the ratio of nucleus length to width
and body length (r 5 2.66) was much weaker.
To illustrate the variability in nucleus shape,
sketches were made of visceral nuclei from
specimens belonging to three different size
classes (Fig. 5). The length to width ratio
ranged from 2.4 to 3.5 among four animals
having body lengths of 18.5 to 20.7 mm, from
1.92 to 2.61 in three individuals between 31.2
and 33.4 mm, and from 1.65 to 2.50 in three
specimens between 42.3 to 44.1 mm.
Lastly, Bonnevie (1920) stated that the
nucleus does not extend above the dorsal surface
of the body in P. hippocampus, while it rises
slightly above the dorsal surface in P. minuta
(Table 3). A qualitative survey of specimens
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Table 5. Characterization of visceral nucleus shape in Pterotrachea hippocampus and P. minuta by
authors subsequent to Bonnevie (1920).
Authority
Pterotrachea hippocampus
Pterotrachea minuta
Tesch (1949)
pyriform and thick
intermediate between P. coronata and
P. hippocampus; length somewhat more
than 3 times breadth
Richter (1968)
short and thick
much narrower and longer than in
P. hippocampus
Taylor and Berner (1970) pyriform and thick
length about 3 times breadth
van der Spoel (1972)
not very slender
slender
Richter (1974)
egg shaped, tapered apically
slender, oval shape; much narrower than in
P. hippocampus
van der Spoel (1976)
less slender than in
P. coronata;
elongated; 3 times as long as broad;
intermediate between P. hippocampus and
P. coronata
Aravindakshan (1977)
pyriform
spindle shaped; height more than 3 times
greatest width
Pafort-van Iersel (1983)
resembles that of P. scutata;
slender, as in P. coronata; length about
length about 2.5 times breadth 3 times breadth (mean 5 3.1;
(mean 5 2.3; range 5 1.9–3.0) range 5 2.2–4.5)
van der Spoel, et. al.
(1997)
oval; less slender than in
P. coronata
elongated; 3 times as long as broad
Figure 4. Length to width ratio of visceral nucleus in relation to total body length (Y 5 2.019 1 3.160)
(r 5 2.66). Specimens identified previously as P. hippocampus shown by solid symbols; those as P. minuta by
open symbols. Body lengths based on lens diameters calculated using the regression equation in Figure 1.
Length to width ratio for P. minuta holotype specimen indicated by a ‘1’ symbol. Specimens from Ocean Acre
samples shown by triangles; those from North Atlantic Plankton Expedition shown by circles.
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Figure 5. Camera lucida sketches of visceral nuclei viewed from right side of animal. Selected animals belong
to three size groups; small (18.5–20.7 mm), intermediate-sized (31.2–33.4 mm), and large (42.3–44.1 mm). For
each sketch, length to width ratio shown to right and body length beneath. Asterisks denote males; all other
individuals females.
examined here indicated that the degree of
dorsal extension of the nucleus above the body
surface decreased with increasing body size; i.e.,
smaller animals corresponded to Bonnevie’s
description of P. minuta and larger animals to
P. hippocampus.
Cuticular structures:
Bonnebvie (1920) stated that female P. hippocampus possessed a broad, rounded papilla on
the right side of the trunk in front of the
nucleus. Because the only specimen of P. minuta at her disposal was a male, she was unable
to determine whether or not such a structure
was present in females of the species. Tesch
(1949) also observed this structure in female
P. hippocampus, referring to it as an ‘obtuse
prominence’. However, he made no mention of
its presence or absence in P. minuta. Van der
Spoel (1976) and van der Spoel, et al. (1997)
reiterated the observations cited above by
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Table 6. Morphological differences, in addition to eye and nucleus shape, between Pterotrachea
minuta and P. hippocampus cited by authors subsequent to Bonnevie (1920).
Character/Authority
1. Cuticular structures:
a. PapillaTesch (1949)
Pterotrachea hippocampus
Pterotrachea minuta
on cutis of right side, just before
nucleus in females
on cutis of right side, just before
the visceral nucleus
not discussed
van der Spoel
(1976); van der
Spoel, et al. (1997)
b. SpotsTesch (1949)
a few spinules on flanks of body
between fin and eyes and at
edges of osphradium groove
van der Spoel
tubercles rare, although living
(1976); van der
specimens show red dots
Spoel, et al. (1997) scattered on the epidermis
Pafort-van Iersel
in large specimens cutis
(1983)
surrounding fin base beset with
small warts
c. Spines anterior to eyesTesch (1949)
in females only; sometimes
vestigial
van der Spoel
in females only; up to 5 tentacular
(1976); van der
protrusions present
Spoel, et al. (1997)
Pafort-van Iersel
sometimes present
(1983)
Newman (1990)
in females only; several present
3. Osphradium location:
Tesch (1949)
linear; a little in front of nucleus
4. Gill number, size and location:
Tesch (1949)
about 8, but number not constant;
surrounding nucleus at top and
on left side
Aravindakshan
confined to left and anterior
(1977)
portion of nucleus
van der Spoel
more and smaller than in P.
(1976); van der
coronata
Spoel, et al. (1997)
Newman (1990)
small and numerous
5. Pedal ganglia location:
Tesch (1949)
not discussed
Okutani (1957)
not discussed
Pafort-van Iersel
same as in P. minuta
(1983)
6. Swimming fin size and location:
Tesch (1949)
not discussed
Taylor and Berner not discussed
(1970)
absent (presumably due to youth of
specimens)
round tuberculate spots on trunk
ventrum, especially in area of fin base
warts supposed to occur on trunk
around fin, but not found in examined
specimens
not discussed
not discussed
absent
absent
supposedly located to left of median
axis of animal, but not appreciably the
case in the material examined
not discussed
not observed
about 10; very small; located near top
of nucleus
not discussed
in front of anterior margin of fin
in front of fin base
just in front of insertion of fin
remarkably small
relatively smaller than in P.
hippocampus
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109
Table 6. (Continued).
Character/Authority
van der Spoel
(1976); van der
Spoel, et al. (1997)
Aravindakshan
(1977)
Pterotrachea hippocampus
Pterotrachea minuta
size not discussed; located
opposite and anterior to nucleus
small; located anterior to nucleus, but
at a relatively smaller distance than in
other species of Pterotrachea
size not discussed; located exactly small; location not discussed
in between nucleus and eyes
7. Swimming fin sucker size in males:
Tesch (1949)
not discussed
van der Spoel
not discussed
(1976); van der
Spoel, et al. (1997)
Aravindakshan
not discussed
(1977)
Pafort-van Iersel
not discussed
(1983)
Tesch. In the present study this structure was
present only in females from 18 mm in length to
adults. Thus, the rounded papilla should be
considered a sexual characteristic in females
that is of no taxonomic use.
Bonnevie (1920) regarded cuticular spots
located on the trunk ventrum as an important
taxonomic character in P. hippocampus that
distinguished two varieties (var. punctata and
var. apunctata) on the basis of their presence or
absence, respectively. Tesch (1949), however,
concluded that this minor difference did not
justify recognition of the two varieties, and
nobody has treated them as valid subspecific
entities since then. Bonnevie also reported that
P. minuta had a few spots on the trunk surface
around the point of insertion and posterior to
the swimming fin. Subsequent authors were not
consistent on their treatment of this character
(Table 6). In agreement, van der Spoel (1976)
and van der Spoel, et al. (1997) indicated that
spots were present on the trunk in P. minuta,
especially around the fin base. Whether or not
this statement was based on personal observations or Bonnevie’s characterization is unknown. However, neither Tesch (1949) nor
Pafort-van Iersel (1983) found any spots (which
they termed spinules or warts, respectively) on
the specimens of P. minuta that they examined.
Because Bonnevie gave the body length of the
holotype animal as 47 mm, Tesch attributed the
absence of cuticular spots in the specimens he
identified as P. minuta to their presumed youth
(maximal size of about 25 mm).
In the present study the presence and
number or absence of cuticular spots were
minute
small
minute
small
determined from a series of 61 individuals
ranging in size from 9.6 to 57.0 mm. The spots
were seen in both sexes. However, their presence and number was related to body size in a
peculiar manner. Among the 13 animals smaller
than 20 mm, spots were absent. Among the 29
individuals between 22 and 35 mm, spots were
present on 21 animals (72%) and averaged
11.1 per individual (among those animals with
spots), with a maximum of 24. For the 19
animals greater than 35 mm, spots were present
on 13 individuals (68%) and averaged 17.1 per
animal (among those with spots), with a maximum of 27. These results are interesting to
interpret in light of the reported inconsistencies
reported above by previous workers. The
specimens identified by Pafort-van Iersel as P.
minuta from the Mid North Atlantic Expedition
all lacked spots. Reexamination of these individuals here showed that on the basis of their
lens diameters all had body lengths less than
21 mm. Since Tesch (1949:44) indicated that his
largest specimen was ‘at most 25 mm long’, it is
conceivable that the actual body lengths of his
animals could also have been less than about 20
mm and, thus, would have been in agreement
with the results of Pafort-van Iersel.
In his description of P. hippocampus, Philippi
(1836) stated that females possessed two series
of three, closely spaced denticles, or spines,
anterior to the eyes. Bonnevie (1920) reported
that these cuticular structures were present in
female P. hippocampus but were absent or
rudimentary in males. Tesch (1949), van der
Spoel (1976) and van der Spoel, et al. (1997)
cited this characteristic for P. hippocampus
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(Table 6). In female P. minuta, however, Pafortvan Iersel (1983) and Newman (1990) stated
that cuticular spines were absent. Hypothetically, then, cuticular spines are present in female
P. hippocampus and lacking in P. minuta. To
test this hypothesis, the presence (and number)
or absence of spines was determined for all
available specimens in the present study (Fig. 6).
Spines were recorded from a total of 22 females
whose body lengths were greater than 30 mm,
but they were absent from all females less than
30 mm and from all males. Where present, the
spines were located along two moderately
elevated ridges on either side of the body midline anterior to the eyes. The number of spines
increased rapidly with increasing body length
above 30 mm. The greatest number of spines
was 10 from a 44.3-mm specimen. These results
refute the above hypothesis that the presence or
absence of cuticular spines distinguishes female
P. hippocampus from P. minuta. Instead, the
spines appear developmentally in females at
body lengths in excess of about 30 mm, and their
number increases with age.
Lastly, Bonnevie (1920) indicated that cuticular tubercles were present along the lateral
muscle bands of the tail and occasionally on the
wall of the osphradium in P. hippocampus, but
such tubercles were absent from these locations
in P. minuta. Tesch (1949) stated that the four
longitudinal muscles in the tail were of no taxonomic importance, and no authors subsequent
to Tesch have made any mention of the tail
muscles or whether or not they are covered by
tubercles. The material available in the present
study supported Tesch’s statement; small tubercles were present in some specimens on the
osphradium wall and on the cutis overlying the
muscle bands (particularly the dorsolateral pair).
However, the condition of the cutis was highly
variable and these structures were, correspondingly, present only in those specimens with an
intact and well-preserved cutis. There was no
evident size relationship between the presence
(and abundance) or absence of the tubercles
among the animals examined.
Osphradium:
The location of the osphradium in relation to
the midline of the body was cited by Bonnevie
(1920) as a difference between P. hippocampus
(middorsal) and P. minuta (somewhat to the
left of the median plane). With regard to P.
minuta, Tesch (1949:44) stated: ‘It is said that
the osphradium is somewhat to the left of the
Figure 6. Number of cuticular spines in relation to body length. Body lengths based on lens diameter, calculated using the regression equation in Figure 1. Males shown by solid symbols; females by open symbols.
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SPECIES DISCRIMINATION IN PTEROTRACHEA
median axis of the animal, but this is not appreciably the case in my material’. No authors after
Tesch have made reference to the location of the
osphradium as a taxonomic difference between
the two species. To address this problem, I
examined 30 specimens across a broad size
range. In contrast with the reports of Bonnevie
and Tesch, the osphradium was distinctly to the
left of the midline of the body in 25 individuals
and was close to the midline, but still to the left,
in the remaining five. Thus, osphradium location followed no size-related pattern, and
appears to have no taxonomic utility.
Gills:
Bonnevie (1920) indicated that the holotype
specimen of P. minuta had 11 gills, while P.
hippocampus had between 12 and 15 (Table 3).
Tesch (1949) stated that P. hippocampus had
about eight gills, although he gave no count for
P. minuta. He considered the number of gills to
be of no taxonomic value. Van der Spoel (1976)
and van der Spoel, et al. (1997) stated that P.
minuta had about ten gills, while P. hippocampus had greater than ten. Other authors
(Aravindakshan, 1977; Newman, 1990) gave
qualitative comments about the gills in P.
hippocampus but said nothing about P. minuta.
Examination of the present material showed
that the number and size of the gills generally
appeared to increase with age. However, the
gills were often in very poor condition or were
missing, which made quantification of this
character difficult to impossible in many cases. I
agree with Tesch that the gills should not be
used as a taxonomic character.
111
Radula:
Bonnevie (1920) provided considerable detail
on radular tooth morphology of P. hippocampus and P. minuta (Table 3). Sketches of
intermediate (or lateral) tooth showed that a
secondary spine was present at the free end
of the tooth in P. minuta, but was lacking in
P. hippocampus. Richter (1968) described the
ontogenetic changes in the lateral teeth in P.
hippocampus, and showed that a large secondary spine was present in the larva, but that
it was reduced in the juvenile and absent in
the adult. Bonnevie also described the median
spine of the central (or rachidian) tooth as
longer in P. hippocampus than in the P. minuta.
This difference was also shown to be ontogenetic by Richter (1968), with the median
spine increasing in length with age. Thus, the
species differences in tooth morphology given
by Bonnevie are not valid, and instead are
developmental, resulting from the comparison
of radulae from animals of different ages.
Buccal teeth:
Bonnevie (1920) indicated that there were 5
or 6 buccal teeth in each of two rows in both
P. hippocampus and P. minuta, but that the
teeth were broad-based in the former species
and narrow-based in the latter species (Table
3). No authors after Bonnevie have included
the buccal teeth as a taxonomic character.
Nonetheless, their number and shape could
serve as valid taxonomic differences that bear
reexamination. To this end, I counted and
measured the length and width of the buccal
teeth from a series of nine specimens ranging in
Table 7. Characterization of buccal teeth from selected specimens identified previously as Pterotrachea hippocampus and P. minuta, including total number of teeth, mean length of the four longest
teeth (using the two longest teeth from each of the two tooth rows), and ratio of length to basal width
of teeth. Body length estimated from lens diameter using regression equation from Figure 1.
Species
Sex
Lens
Diameter
(mm)
P. hippocampus
P. hippocampus
P. hippocampus
P. minuta
P. minuta
P. minuta
P. minuta
P. minuta
P. minuta
male
male
male
female
female
female
male
female
male
0.27
0.30
0.34
0.36
0.39
0.40
0.43
0.49
0.56
Est.
Body
Length
(mm)
11.0
15.3
21.0
23.9
28.1
29.6
33.8
42.4
52.4
No.
Teeth
Mean
Tooth
Length
(mm)
Tooth Length to
Width Ratio
Mean
Range
8
8
11
10
11
11
10
12
10
60
65
88
113
97
99
125
110
175
2.4
2.4
3.6
3.5
3.4
3.4
4.3
3.2
3.0
1.8–3.0
2.0–3.0
2.7–4.6
2.8–4.5
2.0–4.5
2.5–5.0
3.2–6.0
1.8–4.8
2.1–4.2
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R.R. SEAPY
size from 10.0 mm to 52.4 mm (Table 7).
Although animals larger than 20 mm had 10, 11
or 12 teeth (in agreement with Bonnevie), the
two individuals less than 20 mm had 8 teeth.
Tooth length ranged widely in each animal,
with the shortest teeth at the anterior end and
the longest teeth at the posterior end of each
row. The longest tooth was often the second to
last rather than the last tooth. Also, the length
of the largest teeth increased with increasing
body length. To quantify this observation, the
lengths of the two longest teeth from each of
the two rows were averaged for each animal
and compared with body length by regression
analysis. The average length increased with
increasing body length (Y 5 2.38X 1 35.86),
and the two variables were positively and highly
correlated (r 5 1.91).
In addition, Bonnevie’s contention that P.
minuta has narrow-based teeth and P. hippocampus has broad-based teeth was not supported by the present data (Table 7). Among
the teeth in each tooth row the shape was found
to range from narrow-based (for the small,
anterior teeth) to broad-based (for the large,
posterior teeth). To quantify the variability of
tooth shape in each specimen, the length and
maximal width were measured and the ratio of
the length to width calculated. The range of the
ratios for each specimen varied from a low of
2.0 to 3.0 in the 15.3-mm animal to a high of 1.8
to 4.8 in the 42.4-mm individual (Table 7).
Lastly, there was no clear relationship between
the average tooth length to width ratio and
body length, although the average was lowest
(2.4) for the two specimens less that 20 mm
while those larger than 20 mm had ratios of 3.0
or greater.
Male sex organs:
Bonnevie (1920) described the sex organs of
male P. hippocampus as tripartite, consisting of
two broad leaf-like lobes and a finger-shaped
organ, ending in a sucker-like extension (Table
3). She characterized those of P. minuta as
consisting of three small leaves, one of which
was a glandular organ ending in a sucker-like
plate. Gabe (1965) performed a detailed morphological and histological study of the male
sex organs of representative species from the
three families of heteropods. He referred to the
elongate organ as a flagellum and the two leaflike lobes as a penis and as a glandular outgrowth of a basal sac, which receives the ciliated
sperm groove. Although he did not examine
male specimens of P. minuta, he stated that the
male sex organs of P. mutica (5hippocampus)
and P. coronata were essentially identical. The
only author after Gabe to make reference to
the male sex organs was van der Spoel (1976),
who included sketches of the sex organs for
both species, but made no mention of these
structures in the species characterizations. I
examined about 50 Hawaiian specimens over
a wide size range (Seapy, 1985) and found considerable variability in the appearance of these
structures, regardless of animal size. Hypothetically, these differences resulted from the preservation process or to the state of the structures at
the time of preservation. I concluded that this
variability was so great that any structural differences between species were masked in the
preserved specimens.
Pedal ganglia location:
Tesch (1949) reported that the pedal ganglia
were located anterior to the insertion point of
the fin into the trunk in P. minuta. Although not
discussed, his illustration of P. hippocampus
showed the pedal ganglia slightly posterior to
the fin insertion point. Citing his source as
Tesch (1949), Okutani (1957a) also made reference to this location in P. hippocampus, and his
sketch of the species showed the ganglia immediately posterior to the fin insertion point.
Pafort-van Iersel (1983), however, reported
that the pedal ganglia were located in front of
the fin in both species. I addressed this question
previously (Seapy, 1985) using a series of 54
specimens from Hawaiian waters. With reference to the insertion point of the swimming fin,
the pedal ganglia were located just posterior to
it in only one individual (22 mm), but were
situated immediately above it in 21 animals
(12–42 mm), slightly anterior to it in 20 specimens (14–37 mm), and well anterior to it in 12
individuals (21–38 mm). Thus, my results are in
basic agreement with Pafort-van Iersel, and
provide no support for the usage of pedal
ganglia location as a taxonomic character.
Qualitative examination of specimens in the
present study were in agreement with my previous results.
Size and location of the fin and fin sucker:
Although Bonnevie (1920) did not discuss the
size of the swimming fin and fin sucker in relation to overall body size in P. hippocampus and
P. minuta, her sketches of the two species
showed that these structures were proportionally much smaller in the latter species. With
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SPECIES DISCRIMINATION IN PTEROTRACHEA
reference to the small fin and sucker in Bonnevie’s sketches of P. minuta, Tesch (1949:44)
remarked: ‘A point, not mentioned by Miss
Bonnevie but figured by her, is the remarkably
small swimming-fin, which in the male is provided with a minute sucker a little anterior to
the centre of the free margin’. In agreement
with Tesch, Taylor and Berner (1970) stated
that the fin was smaller in P. minuta than in
P. hippocampus. Van der Spoel (1976) and
Aravindakshan (1977) characterized the fin and
sucker in male P. minuta as small, although
neither author discussed the size of either
structure in P. hippocampus (Table 6). In disagreement with van der Spoel, Aravindakshan
(1977:139) gave the location of the fin in P.
hippocampus ‘as exactly in between the visceral
nucleus and the eyes’. Pafort-van Iersel (1983)
did not mention location or size of the fin or
sucker for either species, although she stated
that the sucker was small in P. minuta. In my
earlier study (Seapy, 1985, Figs. 7 and 8), I
showed that two species could not be distinguished on the basis of either fin or sucker size;
i.e., both structures increased in length with
increasing body length. A qualitative examination of specimens in the present study was
in agreement with my previous results, and
revealed no size-related differences in fin location on the trunk.
DISCUSSION
The two main taxonomic characters used to distinguish P. hippocampus from P. minuta have
been the shapes of the visceral nucleus and
eyes. In three studies (Pafort-van Iersel, 1983;
Seapy, 1985; and herein), the shapes of these
structures were quantified by their length to
width ratios using a series of specimens across a
broad range of body sizes. In each case, there
was large variability among the length to width
ratios for the visceral nucleus, which was
reflected in moderately low correlation coefficients between the ratio and body length (r 5
2.66 here and 2.37 from Seapy, 1985). As
explained in the Introduction, this variability
can be related to individual differences in gut
fullness and to preservation effects. Despite this
variability there was a general pattern of
decreasing length to width ratios with increasing body lengths. Small specimens have narrow
visceral nuclei, which can be related, at least in
part, to their sexual immaturity (and lack of
developed gonadal tissue). Intermediate to
large individuals, with progressively greater
113
gonadal and digestive tissue mass, show increasingly greater nucleus width. Although Pafortvan Iersel plotted the nucleus length to width
ratio as a function of body length, she did not
perform regression analyses for the entire data
set or for the two species separately. However,
in an effort to provide a quantitative difference
between the two species on the basis of nucleus
shape, she computed the average length to
width ratios of P. minuta (3.1) and P. hippocampus (2.3). A comparable result can be obtained
from Figure 2 in this study; small specimens
(less than 20 mm) had ratios that averaged 3.0
(ranging mainly from 2.6 to 3.3), while large
animals (greater than about 40 mm) had ratios
that averaged 2.3 (ranging mainly from 2.1 to
2.7).
In contrast with the variability seen in
visceral nucleus shape, eye shape (expressed as
the eye length to retinal width ratio) was
strongly correlated with body length here (r 5
2.86) and in my 1985 paper (r 5 2.85). It is
clear, therefore, that eye shape is superior to
visceral nucleus shape as a taxonomic character.
Based on her analyses, Pafort-van Iersel
(1983:86) reached the same conclusion: ‘. . . in a
number of cases it is hard to decide whether a
specimen belongs to P. hippocampus or to P.
minuta. The most distinctive character proves
to be the shape of the retinal base in the eyes.
Ultimately, it has been possible to divide the
specimens into two groups, P. hippocampus
with a curved retina reaching the lens, and P.
minuta with a not so broad and curved retina’.
Examination of the eye sketches in Figure 5
enables one to understand how Pafort-van
Iersel was able to resolve problems of species
identity using eye shape as the ultimate
criterion. Specimens with an actual body length
greater than about 21–22 mm had the eye type
of P. hippocampus, while those less than 21–22
mm had the eye type of P. minuta. Because
she and other authors did not correct for the
inherent variability in preserved body lengths
using lens diameter, the absence of any individuals with a true body length of less than about
21–22 mm that had the eye morphology of
P. hippocampus was probably overlooked.
Thus, it is my contention that Bonnevie and
subsequent authors have mistakenly identified
young P. hippocampus as P. minuta.
Based on measurement of its lens diameter
(Seapy, 1985), I estimated that the body length
of the holotype specimen prior to net capture
was 19.6 mm, which is less than one-half of
the 48-mm length reported by Bonnevie. Conceivably, the diameter of the lens could have
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decreased over the years during storage of the
specimen in ethanol solution. If so, 20 mm
would be a conservative estimate, and the
actual body length could have been upwards of
25 mm. Regardless, a 20 to 25 mm length would
be reasonable given the range of sizes reported
by previous authors for most of the animals
they identified as P. minuta. Tesch (1949) and
Thiriot-Quiévreux (1973) reported a maximal
body length of 25 mm. Okutani (1957a) stated
that his specimens were less than 20 mm, except
for a 29-mm animal. Richter (1974) reported a
size range of 8 to 14 mm among his specimens.
All individuals examined by Aravindakshan
(1977) were less than 20 mm, except for a 26mm animal. Similarly, with the exception of
a 37-mm individual, the largest specimen
measured by Pafort-van Iersel (1983) was 20.5
mm.
Tesch (1949) and Newman (1990) used the
presence or absence of cuticular spines anterior
to the eyes as a means of distinguishing females
of P. hippocampus from P. minuta, respectively.
The present results clearly show that this is not
a valid taxonomic difference between species.
Rather, it is a secondary sexual feature that
develops in females at a body length of about
30 mm. While examining the specimens in the
present study, I recalled that female P. hippocampus from Hawaiian waters lacked cuticular
spines. To verify this recollection, I reexamined
these specimens and found that cuticular spines
were absent in all individuals except for a
58-mm female which had three, very small
spines. Also the elevated pair of ridges upon
which the cuticular spines are located in the
North Atlantic specimens were represented in
the Hawaiian specimens by two low and flat
hemispherical areas.
Lastly, in my 1985 paper I discussed the findings of Richter (1968) regarding the pterotracheid larvae he had collected over a threeyear period from the Mediterranean Sea. He
described three larval types that were distinctively different in shell morphology, the first
two of which he assigned tentatively to P.
hippocampus and P. minuta, respectively, on
the basis of eye morphology of postmetamorphic individuals. The third larval type had more
tubular eyes, like P. coronata and P. scutata. In
her review paper, Thiriot-Quiévreux (1973)
agreed with Richter that there were three distinct larval types in the Mediterranean, but she
identified the first larval type as P. coronata, in
agreement with the earlier designation by Franc
(1949). If, in fact, the first larval type belonged
to P. coronata, the second to P. hippocampus,
and the third to P. scutata, than a larva distinctive to P. minuta would not exist.
In conclusion, the results of the present study
are in agreement with those I obtained previously from specimens collected from Hawaiian waters in the North Pacific Ocean (Seapy,
1985): there is no justification for the recognition of P. minuta as a species distinct from
P. hippocampus. Because P. hippocampus was
described before P. minuta, the former name
has priority and is herein designated as the
senior synonym. All earlier published records
of P. minuta (see van der Spoel, 1976; van der
Spoel, et al., 1997; and below) should be
referred to P. hippocampus. A list of synonyms
and a paraphrased version of the original
description of P. hippocampus by Philippi (1836)
are given below.
TAXONOMIC ANALYSIS AND SYNONYMY
FAMILY PTEROTRACHEIDAE GRAY, 1843
Genus Pterotrachea Niebuhr (ms. Forskål), 1775
Diagnosis: see van der Spoel (1976:159)
Type Species: Pterotrachea coronata Niebuhr (ms.
Forskål), 1775
Pterotrachea hippocampus Philippi, 1836
Synonymy:
Firola Cuvier Peron & Lesueur, 1810: 64, pl. 1 (fig.
8).—Lesueur, 1817: 7, pl. 1 (fig. 4)
[genus name changed to Pterotrachea by Blainville
(1820); see Smith (1888: 13) for early citations]
Firola mutica Lesueur, 1817: 6, pl. 1 (fig. 1)
[genus name changed to Pterotrachea by Blainville
(1820); see Smith (1888: 15) for early citations]
Firola gibbosa Lesueur, 1817: 6, pl. 1 (fig. 2)
[genus name changed to Pterotrachea by Blainville
(1820); see Smith (1888: 14) for early citations]
Firola Forskalia Lesueur, 1817: 7, pl. 1 (fig. 3)
[genus name changed to Pterotrachea by Blainville
(1820); see Smith (1888: 14) for early citations]
Firola Frederica Lesueur, 1817: 7, pl;. 1 (fig. 5)
[genus name changed to Pterotrachea by Blainville
(1820); see Smith (1888: 14) for early citations]
Pterotrachea Friderici (Lesueur).—delle Chiaje, 1829:
184, 198, pl. 69 (fig. 2) [variously spelled as fridericiana and fredericia]
Pterotrachaea hippocampus Philippi, 1836: 242–243,
pl. 28 (fig. 16).—Smith, 1888: 16 (for early citations).—Zhang, 1964: 208, fig. 66.—Dales, 1953:
1009.—van der Spoel, 1976: 161 (for most citations to
1974).—Okutani, 1957a: 17, pl. 2 (figs. 6, 7), pl. 3 (figs.
2, 4b).—Taylor & Berner, 1970: 237, fig. 8–3d.—
Aravindakshan, 1977: 139, 140.—Magaldi, 1977: 300,
pl. 1 (fig. 9).—Pafort-van Iersel, 1983: 85, figs. 10a,
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SPECIES DISCRIMINATION IN PTEROTRACHEA
11a.—Seapy, 1985: 126–131, figs. 1, 2, 3a–d.—Seapy &
Young, 1986: 139, pl. 1a, c, e, pl. 2d, e, pl. 3a.—Seapy,
1987: 10, fig. 19.—Seapy, 1990: 239, fig. 13—Newman,
1990: 111, fig. 3.15a.—Thiriot-Quiévreux, 1990: 40, fig.
7.—Michel & Michel, 1991: 563.—Vitturi, Catalano,
Colombera, Avila, & Fuca, 1993: 581, figs. 1–11.—
Fosså & Nilsen, 1996: 212.—Thiriot-Quiévreux &
Seapy, 1997: 242, fig. 3.—van der Spoel, et al., 1997.—
Newman, 1998: 807, Fig. 15.147a.—Richter and
Seapy, 1999: 638, figs. 4d, 11, 12d, 13c,d.
Firola Souleyeti Vayssière, 1903: 347.—Vayssière,
1904: 37, pl. 3 (figs. 42–44)
[genus name changed to Pterotrachea by Tesch
(1906)]
Pterotrachea (Euryops) mutabilis Tesch, 1906: 88, pl.
13 (figs. 86–89)
Pterotrachea (Euryops) xenoptera Tesch, 1906: 88, pl.
13 (figs. 90–91)
Pterotrachea xenoptera Franc, 1949: 223
Pterotrachea (Euryops) orthophthalmus Tesch, 1906:
89, pl. 13 (figs. 92–94)
Pterotrachea (Eupterotrachea) hippocampus var.
apunctata Bonnevie, 1920: 13, pl. 3 (fig. 34)
Pterotrachea (Eupterotrachea) hippocampus var.
punctata Bonnevie, 1920: 13, pl. 3 (fig. 35)
Pterotrachea minuta Bonnevie, 1920: 13, pl. 4 (figs.
47–52).—Dales, 1953: 1009.—Zhang, 1964: 209, pl.
67—van der Spoel, 1976: 163 (for most citations to
1974).—Okutani, 1957a: 20, pl. 2 (fig. 8), pl. 3 (figs.
3,4c).—Okutani, 1957b: 136, 137.—Furnestin, 1961:
312, fig. 17a.—Taylor & Berner, 1970: 238, fig. 8–3c.—
Aravindakshan, 1977: 141, 142.—Magaldi, 1977:
300.—Furnestin, 1979: 180.—Pafort-van Iersel, 1983:
85, figs. 10b, 11a.—Seapy, 1985: 127, fig. 3e.—Newman, 1990: 112, fig. 3.15c,—van der Spoel, et al.,
1997.—Richter and Seapy, 1999: 638, fig. 13e.
Questionable synonyms:
Pterotrachea quoyana (d’Orbigny, 1836) was listed by
van der Spoel (1976) as a questionable synonym of
P. hippocampus. This species was not reevaluated as
part of this paper and, hence, is not cited above as a
synonym. P. minuscula Issel, 1910 was included
among the synonyms of P. hippocampus by Tesch
(1949). Because the paper by Issel could not be
located, the status of this species is not reevaluated
here.
115
Van der Spoel (1976) listed P. microptera Tesch,
1906 as a questionable synonym under P. minuta, in
agreement with Tesch (1949). However, Tesch (1949)
also listed it as a questionable synonym under P.
coronata. Based on the original illustrations in Tesch’s
1906 paper showing the visceral nucleus as elongate
and narrow, P. microptera is most probably a synonym of P. coronata. It is herein removed from the
synonymy of P. hippocampus.
Van der Spoel (1976) listed P. peronia (Lesueur,
1817) as a questionable synonym of P. hippocampus.
Based on Lesueur’s original figure and the description
of the species, it is thought that this species represents
a junior synonym of P. coronata and, hence, is herein
removed from the synonymy of P. hippocampus.
Original description (condensed from Philippi, 1836):
Based on a female specimen, 67.5 mm in body length.
Body gelatinous, subcylindrical and colorless. Visceral
nucleus pyriform; violet-blue posteriorly and rosecolored anteriorly. Proboscis elongate (almost 18
mm). Two eyes, distant from each other, in the angle
formed by the proboscis and the body. Eyes rather
large and black, with subspherical, crystalline lenses.
Two rows of three denticles in front of eyes. Tail compressed, 18 mm long and 6.8 mm wide, carinate, with
blunt and bilobed end. Tail and middle part of body
on both sides with a double series of rough tubercles.
Visceral nucleus pyriform, 6.8 mm long and 4.5 mm
wide, bearing gills (not very expanded) anteriorly.
Swimming fin subcircular, 11.3 mm long and 10.1 mm
high, broadly attached at the base and furnished in
the middle with a saucer-shaped sucker in seven
specimens (lacking in the remaining six specimens).
Red filament, almost 7 mm long, encircled by a short
fold of conspicuous red cutis, about 4.5 mm anterior
to the visceral nucleus in specimens with suckers (no
vestige of these structures in the six specimens lacking
suckers). (Note: measurements were given as ... [5
one line 5 2.25 mm] and .. [5 12 lines 5 27 mm])
Holotype:
Not designated. Not traced; but presumed not to be
extant. Type series based on 13 specimens collected
23 March 1832.
Type Locality:
Names removed from synonymy:
Van der Spoel (1976) questioned whether P. hyalina
delle Chiaje, 1829 represented a synonym of P. hippocampus. Philippi (1836), on the other hand, listed it as
a synonym of P. hippocampus. Tesch (1906) attributed the authorship of P. hyalina to Forskål and
noted in his figure legend of P. hyalina that it probably belonged to the genus Firoloida. Tesch (1906)
also raised doubts about the validity of the subspecies
(or variety) P. hyalina cristallina (delle Chiaje, 1843),
since it combined anatomical features from both
Firoloida and Pterotrachea. P. hyalina and P. hyalina
crystallina are hereby removed from synonymy.
ITALY, Sicily, Panormi (modern equivalent is
Palermo).
ACKNOWLEDGEMENTS
Specimens from the Ocean Acre study were provided
by M. Sweeney, National Museum of Natural History,
Washington D.C. Additional animals from the Ocean
Acre study and specimens from the Amsterdam
Mid North Atlantic Plankton Expedition were made
available by S. van der Spoel and R. Moolenbeek,
Zoologisch Museum, University of Amsterdam. D.
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116
Page 116
R.R. SEAPY
Brown, California State University, Fullerton assisted
with the translation of the Latin species description of
Pterotrachea hippocampus. F. G. Hochberg, Santa
Barbara Museum of Natural History, provided valuable advice on taxonomic matters and critically
reviewed and improved an earlier version of the
manuscript.
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