A new species of Fissurellidae (Gastropoda: Vetigastropoda) from the deep-sea off the eastern Pacific coast of Mexico

2017·4 MB·English

by  Nancy Yolimar Suarez-Mozo

THE NAUTILUS 131(4):24()-245, 2017 Page 240
A new species of Fissurellidae (Gastropoda: Vetigastropoda) from
the deep-sea off the eastern Pacific coast of Mexico
Nancy Yolimar Suarez-Mozo Daniel L. Geiger
Ciendas del Mar y Liniiiologi'a - Graduate Program Santa Barbara Museum of Natural History
Universidad Nadonal Autonoma de Mexico 2559 Puesta del Sol
Mazatlan, Sinaloa, MEXICO Santa Barbara, CA 93105, USA
[email protected] [email protected]
ABSTRACT Universidad Nacional Autdnoma de Mexico (UNAM)
research vessel El Puma along the western coast of Baja
The present article describes Fissurella hendrickxi, a new deep-
California Sur and in the Gulf of Cidifoniia. Station depths
sea gastropod species found off the Pacific coast of Mexico (Baja
were estimated with a SIM RAD echo-sounder. Tem¬
Peninsula; Gull of California), at 650-837 m depth, collected by
perature and dissolved oxygen measurements were col¬
the T.alud X\' and Talud X projects. Fissurella hendrickxi was
lected 20 m above the secifloor with a Seabird CTD
classified according to shell sculpture, radula, epipodium, and
multisensor probe. Ox'vgen measurements were checked
ctenidial stnictnre. It is remarkable for its verv' thin shell, which
covers the entire animal. by titration (Strickland and Parsons, 1972). Moqrhological
descriptions include the following dimensions: length (L),
Additional Kinjtvords: Deep sea, Fissurella, continental slope
width (W), and height (H). Fixed specimens were photo¬
graphed for their external anatomy. Specimen preparation
ancl SEM imaging were performed following Geiger et al.
(2007). Cross sections of shells were imaged from broken
INTRODUCTION
pieces. Measurements were t;iken from a middle section
and a section conhiining the pcuts of the foramen.
Recent siiiveys of deep-water endronments oil tiie Pacific
Specimens are deposited at the Santa Barbara Museum
coast of Mexico have discovered new inolluscan species.
of Natural History (SBMNH), and the Regional Collec¬
Such studies seldom )4eld moUusk Scunples, because avciilable
tion of Marine Invertebrates at the Mazatlan Marine
Siunpling techni(|ues tme not tilways adecpiate or only few
Station, UNAM, in Mcizatlan, Mexico (EMU-ICML).
sediment Scunples are collected, thus preventing a diorough
Abbreviations used in tlie figures are: an: anus; ct: cephcilic
inventory of the continentcil shelf, slope, mid the abyssiil pkiin
tentacle; et: epipodi;il tentacle; ey: eye; fo: foramen; ft: foot;
(Zarnonuio et ;il., 2013; McLeiin mid Geiger, 1998).
gi: gill; gs: gill suspensory stiilk; mb: mantle border;
The Fissurellidae comprises four subfamilies: Fissur-
mt: mantle tentacles; mo: mouth; sn: snout.
elliuae, Diodorinae, Emirnginulinae, and Ilemitominae, with
Fissurellinae contidning sfx genera, which ime diagnosed by
shell and radular characters (Tliiele, 1891; 1912; 1929;
SYSTEMATICS
Mcl.^an, 1984a; 1984b; Hickman; 1998). Members of the
Fissurellidae ime most fre(|uently found in the intertidiil (tr Class Gastropotla Cuvier, 1797
sh;illow waters worldwide and are not as prevcilent in deep Suborder Vetigastropoda Salvini-Plawen, 1980
waters. Some genera and species of Fissurellidae have been Family Fissurellidae Fleming, 1822
recorded in deep waters of the ettstem Pacific off South Subfamily Fissurellinae Fleming, 1822
America (McLean and Geiger, 1998; Araya and Geiger,
2013). McLean (1971) documented deep-water Fissur¬
ellidae species [Enuirginula vehscoemis Shasky, 1961, Genus Fissurella Bruguiere, 1789
Zeidoi-aflahellum (Dtill, 1896), and Cranopsis expama (D;ill,
Type Species: Fissurella nimhosa Linnaeus, 1758 (by
1896)] in the Gulf of Gcdifomia anchor ;dong the Baja
monoty]ry).
Peninsula with bathymetric ranges tmound 200 m.
Fissurella hendrickxi new species
MATERIALS AND METHODS (Figures 1-18)
The new species was collected during the Talud X and Diagnosis: Shell up to 42.9 mm; fonunen elipticcil, cen¬
Talud X\' projects (2007 and 2012), on board the tral. Shell extremely thin (-0.1 mm). Specimens smooth
N.Y. Suarez-Mozo and D.L. Geiger, 2017 Page 241
Figures 1—13. Fissurella hendrichxi new speeies. Holot\pe, SBMNH 457424. 1. Dorsal view. Scale bar =10 inm. 2. Ventral vaew.
Scale bar = 10 min. 3. Holoty|re, lateral view. Scale bar = 10 min. 4. Shell tliickness (SEM). Scale bar = 100 p-in. 5. Fissurella
hendrichxi new species (small specimen), EMU-ICML 11338. Scale bar = 10 mm. 6. Eoramen with tentacles and remnants of shell.
Scale bar = 5 inin. 7. Detail of eye, ceplndic tentacle and epipodial tentacle. Scale bar = 5 mm. 8. Right gill, epipodium, foot, eye,
cephalic tentacle, snout, and mouth. Scale bar = 10 nun. 9. Rectal opening v\ath granular fecal matter. Scale bar = o mm. 10. Mantle
border and mantle tentacles above foot. Scale bar = 2 mm. 11. Enlargement of posterior tentacle surrounding foramen. Scale bar =
1 mm. 12. Bursicle. Scale bar = 100 |xin. 13. Enlargement of bursicle. Scale bar = 100 jcin.
Page 242 THE NAUTILUS, Vol. 131, No. 4
Figures 14-18. Fissiirella hendrickxi new species. Radula under SEM. Parat\pe SBMNH 235544. 14. Entire radula. Scale bar =
2 min. 15. Whole width of radula. Scale bar = 1 mm. 16. Central field wth rachidian tooth and lateral teeth. Scale bar = 200 |j.m.
17. Lateromarginal plate Scale bar = 200 lam. 18. Marginal teeth. Scale bar = 100 p.m.
N.Y. Suarez-Mozo and D.L. Geiger, 2017 Page 243
due to erosion at top, concentric lines at sliell bases, small tentacle located on each side of snout, each tentacle ta¬
specimens vvdth primarx’ and secondarv cords. External pering gradually (wider at base tlian at tip), tip pointed,
shell color dull whiti.sh. with different folds around tentacle, slightly shorter tlian
snout. Foot thick, 60% of the shell length.
Description: Shell height moderate (about 30% of
length), outline elliptical, a bit narrow at posterior end Mantle Organs (Figures 10-13):
(Figures 1-3). Width about 60-70% of length. Fora¬
Mantle margin close to shell, smooth exterior fold, interior
men central and conical, 20-22% of length (Figures 6).
fold wider than middle fold; mantle tentacles in middle
Shell extremely thin (Figure 4): callus of foramen
fold; mantle margin of foramen similar. Gill hvpertro-
0.16-0.17 mm reminder of shell 0.1 mm. Profiles
phied, filaments symmetrical, with rounded tip; bursicles
straight. Radial sculpture of alternating primary,
present. Anus elliptical, located at posterior end of pallial
secondary cords regularly spaced. Concentric sculp¬
cavity.
ture generally weak, strongest close to edges. Farger
specimens with concentric lines at shell bases, radial
scnlptnre absent. Small specimens with radial and Radula (Figures 14-18):
concentric sculpture (Figure 5). Foramen area eroded.
Rachidian tooth trapezoidal, broad. Five lateral teetli,
Color external dnll whitish; inner surface whitish,
with narrow inner teeth. Fateromarginal plate triangular,
glossy.
without projections, sinuous distal edge. Marginal teeth
with spoon-shaped pointed tip, with fine denticles on each
Head and Foot (Figures 7-9): side of the apical margin.
Eyestalk narrower than cephalic tentacles, approximately
Type Material: Holotype SBMNH 457424: 34.7X
Va of cephalic tentacle length, located just posterior to
10.6X22.7 mm (FXWXH), 4 paratypes, all from type
origin of cephalic tentacles. Eye almost half as witle as
locality: SBMNH 235544: 42.9X11.5X22.3 mm, 32.9X
chameter of eyestalk. Snout cylindrical, tapering, sur¬
10.93X22.0 mm (FXWXH), EMU-ICML 10965: 35.6X
rounding central mouth. Epipodium with approximately
22.3X11.9 mm (FXWXH), EMU-ICML 10966: 30.2X
34-36 tentacles arranged in single horizontal row ter¬
20.7X8.2 mm (FXWXH).
minating at neck; tentacles varying in size by factor two,
larger ones approximately as long as eyestalk. Cephalic
Type Loeality: Baja California Sur Peninsula, Mexican
Pacific, Mexico, Talud XV, St. 5D, 23°16'58" N;
110°20'42" W, 650-665 m (Figure 19).
li6°48 0'W 113“9.0’W 109°30 0'W
Other Material Examined: Seven specimens, EMU-
z ICML 11338, Talud XV st. 5D, Baja California
O
Sur Peninsula, Pacific Ocean, Mexico, 23°16'58" N,
110°20'42" W; one .specimen, EMU-ICML 11339,
Talud XV, St. 20, Baja California Snr Peninsula,
Pacific Ocean, Mexico,' 26°30'42" N, 113°56'0" W;
one specimen, EMU-ICML 11340, Talud X, St. 5,
Z Gulf of Ccilifomia, Mexico, 28°14'50" N, 112°24'53" W.
orN
o
O Environmental Conditions: Dissolved oxygen, 0.08-
CN
0.15 ml02/l; temperature, 6.2-8.4°C; salinity, 34.55-
34.68%o. ^
Etymology: Named after Michel E. Hendrickx (Insti-
Z
he tuto de Ciencias del Mar y Limnologia, Mazatlan, Sinaloa,
•r r
csO Mexico), who for long time has long studied the benthic
CM
fauna of the eastern Pacific Coast of Mexico, in particular
from off the Baja Peninsula and the Gulf of Ctilifornia.
Comparisons: The radula with veiy large lateral tooth
Z
rosi 5, whose tip ciligns with the lateral teeth of the subse(]uent
c row (see McLean and Kilbuni, 1986) places our species in
r4
rsi
FLssurellinae, and not in Emarginulinae, which includes
the genus Stroinboli. The absence of an internal thick¬
ening around the foramen differentiates the species
Figure 19. Distribution of sampling stations where specimen
from the otherwise similar Diodora. Among the genera
of Fissurella hendrickxi new species were collected during
the Talud X\^ and X surveys off the western coast of the Baja in Fissurellinae, genera other than Fissurella eitlier ex¬
California Peninsula and Gulf of California (A = tyjre locdity). hibit strong shell reduction {Amhlijcliilepas, Letirolepas,
Page 244 THE NAUTILUS, Vol. 131, No. 4
Macroschisma), or show strong propodial elalrorations Fissurella hendrickxi was found in an environment
(Dendwfissurella). All approximately 46 recent species of under hy^^oxic conditions, which characterizes this region
Fissurelhi have rmich thicker shells than the new species. of the eastern Pacific, where the oxygen minimum zone
Tlie two species overall most similar to Fissurella exhibits significant latitudinal variations in depth, thick¬
lieiulrickxi are in genera other than Fi.sstireiki; these are ness, and intensity (Helly and Levin, 2004). Whether the
Diodora codoceoae (McLean and Andrade, 1982) and enlarged epipodium in the species is an adaptation to
StroinboU heehei (Hertlein and Strong, 1951). They deep-water conditions remains unknown. The compara¬
share a large and thinner than nsual shell with a large tively large gill is remarkable, and additional, indirect
foramen that is conical in shape, and the interior shell evidence that the species may he adapted to that par¬
color is white. Diodora codoceoae and S. heehei differ ticular environment.
from the F. hendrickxi in their fleshy mantle that fully Specimens described here were collected from the
envelops the edge of the shell and radial rihs that are continental slope region at depths >200 m. Larger or¬
nniformly fine, with no distinction between primary and ganisms feature decreased shell thickness, a potential
secondaiy ribs (McLean and Andrade, 1982). They both adaption to low energy environments. McLean (1984c)
also have a much sturdier shell than F. hendrickxi and noted that the limpet shape may prove advantageous, as it
tlie sculpture is stronger in S. heehei and D. codoceoae. provides protection through clamping agciinst the sub¬
The shells of both species are noticeably thicker: D. stratum. Species living on soft bottoms can no longer
codoceoae 1.05 mm at length of 36.5 mm (SBMNH clamp down, and the protective function of a thick shell
172216); S. heehei 1.03 mm at length of 31.75 mm does no longer apply.
(SBMNH 118681). Fissurellidae is an interesting lineage with respect to
shell reduction, including complete loss of the shell in
Remarks: Fissurella hendrickxi was collected just be¬
Buchanania. Reduction of shell thus far has mostly been
low the oxygen minimum zone < 0.5 ml O /I (OMZ); fully
2 achieved by reduction in size while maintciining shell
oxygenated seawater can hold >7 ml O /I (Levin 2002).
2 thickness. Examples of moderate reduction include
While die oxygen measurements were taken some 20 m
Megathnra and Scuta.s, while extreme reduction is en¬
above the sea floor (due to equipment limitations), it gives
countered in Macro.schisnui. Fissurella hendrickxi, on the
a reasonable indication of the conditions previiiling in the
other hand, has reduced shell thickness while retciining
species habitat.
a large size. It is the only species in Fissurellinae with fully
Shell sculpture changes with growth. Small specimens
grown shell so thin that it does not offer any protective
(smallest specimen IS mm) have radial and concentric
function anymore (The specimens recovered had gonads
elements whereas larger (>35 mm) specimens only have
indicating maturity.) Similarly thin shells are only known
concentric sculpture at the shell margin. This difference
from deep-water Enuirginulinae, but those are overall
may he accounted for by erosion and/or pliysical wear of
much smaller (-2-10 mm: McLean and Geiger, 1998).
the shell. However, low carbonate assimilation levels or
adaptive changes among large organisms may also play
a role. ACKNOWLEDGMENTS
Tlie epipodium, a complex of sensory or tactile stnic-
We would like to thank the ICML researchers who
tures located on the sides of the foot under the shell
collected the specimens, Michel Hendrickx, and the
margin of the vetigastropods (Macdonald and Maino,
T4LUD project. The authors are grateful to Jose Salgado
1964; Cox, 1962; Crisp, 1981), has proven useful in tax¬
Barragan, Laboratorio de Invertehrados Bentonicos
onomic and systematic classification (Hickman and
(LIB), Unidad Academica Mazatlan, ICML, UNAM,
McLean, 1990, Geiger, 1999; Collado, 2008; Collado
for tciking the photograph in Figure 5. The Talud X\^
et ak, 2012). The epipodium of F. hendrickxi is particu¬
and Talud X research cruises were funded by the Uni-
larly well-developed compared to other species in the
versidad Nacion;il Autonoma de Mexico cuid CONACyT.
genus. This enlargement may be an adaption to extreme
This study Wits also partly supported by CONACyT (Project
environmental conditions such as low oxygen concen¬
179467), as (NYSM) receives a CONACyT graduate
trations or depth. Alternatively, it may improve mobility
studies grant. Part of the material included in this
and tactile sensitivity in soft sea-heds.
contribution was reviewed during a stay of NYSM at the
Santa Barbara Museum of Natural History; thanks to
DISCUSSION Paul Valentich-Scott and Henry Chaney for their assis¬
tance. We appreciate the comments of Alexander Niitzel
Tlie diversity of deep-sea mollusks in the Pacific coast of
and an anonymous reviewer, which helped improve the
Mexico is not well documented. Most species of Fissur-
manuscript.
ellidae from that area occur in relatively shallow water
(0-50 m) on hard substrates. Few deep-water and soft sea¬
bed species are known [e.g., Coiimepta giizmani Araya
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