A new genus and two new species of deep-sea gastropods (Gastropoda: Vetigastropoda: Gazidae)

2012·7.5 MB·English

THE NAUTILUS 126(2):57-67, 2012 Page 57
A new genus and two new species of deep-sea gastropods
(Gastropoda: Vetigastropoda: Gazidae)
Carole S. Hickman
UniversityofCalifornia
Departmentoi Integrative Biology
and
Museum ofPaleontology
Berkeley, CA94720-3140 USA
[email protected]
ABSTRACT (Hickman and McLean, 1990; Hickman, 1996, 1998) is in
increasingconflictwiththe results oi more recent molecu-
Anewgenusandtwonewspeciesofdeep-seavetigastropodgastro- lar analyses (e.g., Geiger and Thacker, 2005; Yoon and
podsextendknowledgeoltheuniqueshellmorphology,radula,anat- Kim, 2005; Williams and Ozawa, 2006; Kano, 2008;
omy, ecology, and distribution ol a familygroup ofundetermined
relationship to other vetigastropods. Anomphalogaz-a moluccensis Williams et ah, 2008, 2010). Although monophylyofsome
newgenus and newspecies is the first record of die familyin die ol the morphologicallybased subfamilies andtribes iswell
IndonesianbiogeographierealmofWallacea.Ccdbgazacohnaninew supported by uew genetic data, there have been some
species is die first record of die familygroup from the Australian major realignments oftheir relationships to one another.
Plate.Determinategrowdiinallknowngazidspeciesisexpressedin New morphological and/or molecular data have led to a
apronouncedthickeningandreflectionofthefinallipalongwidia revised working classification (Bouchet and Rocroi, 2005)
descendingsuture. Indieumbilicatespecies,determinategrowdiis andredefinitionsofTrochidae,Turbinidae, andTrochoidea
alsomarkedbyformationofathin reflectedcallus thatpartiallyor
(Williams et ah, 2008).
fully isolates a hollow umbilical chamber. Unique features of die Some of the most interesting realignments are
Gazid radula include extremely elongated marginal teedi with
stronglyserrateshaftsandanunusualpatternofintegrationinwhich among higher taxa restricted to habitats in the deep
rowsofmarginaltootiibasesandcuspsarealignedinseparaterowsof sea (>200 meters). Recurringfeatures thatappeartobe
rachidianandlateralteetii. Distinctive anatomical featuresinclude convergent in deep-water vetigastropods include minute
expandedoralsurfaceofthesnout, antero-lateralextensionsof die shell size (<5 mm), reduced shell thickness and visibility
foot, and an enlarged liindgut. Numerous repaired breakages of ofnacre (tabular aragonite) through a thin exterior layer,
delicategazidshellspriortoformationofdieterminallipsuggesthigh extremethinningorputativelossolnacre,secondarylossof
predationpressure.Occurrencesinregionsofmedianeandsulfide coilingresultinginalimpetshellform, enlargementoithe
seepage suggest diat diese relatively large deposit-feeding gastro-
hindgut associated with deposit feeding, elaboration of
podsarenutritionallylinkedwithunconventionalcarbonsources.
Original description of the family group as a tribe within structures for sperm transfer and sperm storage, and, in
MargaritinaeThiele, 1924wasbasedon analysis ofmorpholog- somecases,hermaphroditism.
icalfeatures. Subsequentmolecularsequencedatahave shown Examplesofhypothesizedmolecularunmaskingofcon-
that Margaritinae is not monophyletie, and some deep-water vergence include the recognition oftwo discrete clades of
species described under Margarites Gray, 1847 may be more minute slit-shells formerly united under Seissurellidae
closely related to the gazid species described herein. Because (Geiger and Thacker, 2005) and recognition of a close
classificationofvetigastropodfamilygrouptaxaiscurrentlyina relationship among minute shells of seguenziiform taxa,
state of flux, this treatment abstains from traditional ranked
classification and uses the family-group ending “-idae" in a large- and small-shelled deep-sea trochiform taxa, and a
provisionalsense until completephylogenies areavailable. number of minute skeneiform taxa (Kano, 2008). Taxon
sampling for molecular phylogenetic analysis is still prob-
Additional keywords: bathyal, chemosynthesis, methane, sul- lematic and difficult for the many deep-sea taxa that are
fide, coldseep. MoluccaSea, Australia, depositfeeding known only from shells and occasional formalin fixed
specimens inwet collections.
A majorgap in samplingis thatofthe deep-sea family-
group Gazidae Hickman and Mclean, 1990. Eight spe-
INTRODUCTION cies in two genera, Gaza Watson, 1879, and Callogaza
Dali, 1891, have many shared features (Hickman and
Morphological support for monophyletie vetigastropod McLean, 1990)thatunitethemphylogenetically(Hickman,
groups, including monophyletie Turbinidae andTrochidae 1996, 1998). These include shared character states for
Page 58 THE NAUTILUS, Vol. 126, No. 2
38 of 40 radular characters (Hickman, 1996). However, Callogazacolmaninewspecies
the original placement of gazids as a sister group to (Figures 1-10, 12, 14-15)
margaritids (Hickman and McLean, 1990: Hickman, —
1996) has not been tested by molecular sequence data. Gaza (Callogaza) sp. Hickman and McLean, 1990,
A recent review of Gaza and Callogaza and description figs. 53b, c, e, f. (originallymislabeled; reported cor-
rectlyhere)
of a ninth species from Brazil (Simone and Cunha,
2006) did not address relationships, but it underscores Description (Figures 1-8): Shell width (up to
the global distribution of the group and the potential 23.3 mm) exceeds shell height (up to 17.4 mm), and final
for undocumented species. whorl height exceeds that of spire. Aperture is strongly
Molecularsequencedataformargaritidspecies resulted prosocline, inclined to axis ofcoiling at an angle of50°.
in a new phylogenetic hypothesis ol the relationship of Terminal lip both thickened and reflected and marked
the familygroup to othervetigastropods (Williams et al., by a descending suture. Thin, transparent parietal Callus
2008). However, subsequent analyseshavedemonstrated continuous from suture to umbilicus,where it is reflexed
that the group is not monophyletic (Williams et. al., as a thin, slightly convex covering, creating a closed
2010). Further molecular genetic analyses are likely to umbilical chamber. Most abapical of four spiral cords
alter the relationship of gazids and margaritids to each marks periphery ofshell, and suture follows fourth spi-
other as well as to other vetigastropods (Williams, pers. ral. Most apical spiral cord separates a slight shoulder
comm., 2011). from rest of whorl. On shoulder, 15 very fine spiral lines
The objectives of this paper are (1) to describe a new crossed by slightly stronger, finely spaced axial lines to
gazid genus and two new gazid species, and (2) to pro- produce a very finely cancellate surface (Figure 7). A
vide new data highlighting the unusual features of the similarly fine cancellate surface occurs between each of
group, its biogeography, its ecology, and its role in the pairs of spirals between shoulder and periphery. There
deep sea. are 27 very finely incised spiral lines on base (Figure 8).
Thefamilygroupending-idaeisusedprovisionallyand Shell pigmentation consists ofalternating tan and white
without placing Gazidae into a ranked classification of patches on spiral ribs, with two spiral rows of prominent
highertaxaofvetigastropods. Itdoesnotalteritscurrently white blotches on base. Nacre visible onlythrough small
unresolved relationship to the familygroup Margaritidae, windows of transparent shell material and only when
although morphological evidence is presented to sug- shell is moved, generating lustrous flashes. Protoconch
gest that some deep-water species currently assigned to is small, glossy, and of 1.5 whorls.
Margaritidae mayrequirere-allocationto Gazidae. Radula (Figures 9-10, 12): Rachidian is largest tooth
Abbreviations for specimen repositories are: AMS, in central field. Rachidian tooth with broad, ovate base
Australian Museum, Sydney; LACM, LosAngeles County with triangular over-hanging cusp that emerges directly
Museum of Natural History, Los Angeles; UCMP, from base and is finely denticulate along both margins
University of California, Berkeley; USNM, National (Figures 9, 12). Seven pairs of lateral teeth present,
Museum of Natural History, Smithsonian Institution, also with broad bases and triangular, denticulate cusps
Washington, DC. (Figures 9, 12). Inner portion of each lateral base is
obscured by overlappingbase ofadjacent tooth. Cusp of
each lateral tooth directed toward midline, overhanging
SYSTEMATICS outerportion ofbase ofadjacent lateral tooth (Figure 9).
Outermost lateral teeth with elongate shafts and nar-
Vetigastropoda (unranked) rower, longer cusps increasingly curved inward toward
Family Group Gazidae Hickman and McLean, 1990 rachidian. Between outermost lateral and marginal teeth,
(unclassified) in position occupied by lateronrarginal plate in general-
ized troehoidean radula, there are several irregularly-
Genus Callogaza Dali, 1881 developed tooth bases that have failed to develop shafts
and cusps (Hickman and McLean, 1990, Figure 53E,
Type Species: By original designation, Callogaza p. 92). Marginal teeth (Figure 10) with extremely long,
watsoni Dali, 1881. Recent, offHavana, Cuba, 24°34' N, well-developed shafts and long, narrow, overhangingden-
83°16' W, 177 fathoms. Distribution: Northern Cuba ticulate cusps. Marginal cusp rows and base rows do not
south to Brazil, 117-500 fathoms. correspond sensu Hickman, 1984a). Prominent serration
(.
of the marginal shafts (Figure 10) is a unique feature.
Description: Shell of 1.5 smooth protoconch whorls Outermost marginal teeth have unusually broad shafts
and 6 teleoconeh whorls with distinct fine spiral and and cusps and may be partially or fully fused to one
axial sculpture. Smallerthan Gaza Watson, 1879 (width < another (Figure 10).
25 nnn), relatively broader, and prominently pigmented Exterior Anatomy (Figures 14—15): Deep transverse
with alternatingwhite and brown splotches or fine spiral groove (inferred pedal gland) present along anterior
lines on a beige background. Teleoconeh whorls shoul- margin of the propodium. In retracted and preserved
dered and finely carinate. Umbilical callus thinner than animal, anterior propodium and mesopodium folded
in Gaza andconvexwhen completelycoveringumbilicus. under and against sole of foot, with oral disk of snout
C. S. Hickman, 2012 Page 59
Figures 1-8. Callogaza colmani new species. 1. Apertural, 2. Basal, and 3. Apicalviews ofthe holotype, AMS 115689, height =
17.4mm.4.Apertural,5. Basal,and6.Apicalviewsofparatype 1,AMS 115689a,height= 17.9mm. 7. Detailsofsculptureonapical
whorls ofholotype. 8. Details ofsculptureonbaseofholotype.
pressed against fold. Large snout cylindrical, expanding inentupraisedpapillae, sixonrightsideandseven on left.
distallytoatentacularmarginsurroundingbroadoraldisc (Itis notknownwhetherthesepapillaeareinnervatedand
densely coveredwith shorter tentacles. Mouth lies within sensory in function or glandular and secretoiy, although
longitudinal groove on oral disc. Large, black-pigmented they are referred to here as epipodial sense organs. They
eyes lie at distal ends ofshort, thick, dorsoventrally flat- are similar in appearance to the epipodial sense organs
tened eyestalks. Innerbasal margins ofeyestalks continue that are pairedposteriorlywith each of the epipodial ten-
over bases of cephalic tentacles, joining small crescent- tacles.) Seven epipodial tentacles present on right side of
shaped cephalic lappets. Lappets have entire margins animal and six on left. Each tentacle and its basal sense
and do not reach midline of snout. Cephalic tentacles organ arise beneath a separate, thin, crescent-shaped flap
relativelylongeven in theircontracted state. No evidence of epipodial tissue. Epipodial flaps partially overlap one
of micropapillae on eithercephalic orepipodial tentacles, another in imbricate fashion. Epipodial tentacle length
butthis maybe apreservation artifact. Left (inhalant) and decreases posteriorly on both sides. On left side, ante-
right (exhalant) neck lobes large andwell-developed flaps riormost epipodial tentacle lacks a flap and basal sense
oftissuewith simple margins. Beneatheachnecklobe and organandislongerandsetapartfromotherfivetentacles.
continuingposteriorlyalongside offootis a rowofprom- Mantle cavity ofholotype not dissected, but long free tip
Page 60 THE NAUTILUS, Vol. 126, No. 2
Figures 9-13. Radulae. 9-10. 12. Callogaza colmani new species. 9. Raehidian and left lateral teeth ofholotype, AMS 115689,
scalebar= 100 pm. 10. Rightmarginalteeth ofholotype,bar= 100 pm. 12. Detailofraehidianbase andserrationofraehidianand
innerlateralcusps ofholotype, scalebar=40 pm. 11. Raehidian andleft lateral teeth ofGazasuperba Dali, 1881, UCMP D-3763.
13. Raehidianandinnerlateralteeth ofMargaritessimbla Dali, 1913, LACM 71-374.
of bipectinate ctenidium projects from beneath mantle of spiral and axial sculpture and pigmentation pattern.
margin ofpreserved specimen. Although the pigments are similar, they are distributed
differently, as in the arrangement ol white splotches on
Remarks: The new species is distinguished from the base of the shell. The radula and soft anatomy are
Callogaza watsoni, by complete nacreous terminal clo- unknown for both C. watsoni and C. sericata but the
,
sure of the umbilicus and relatively higher spire. The shells have been adequately figured by previous authors
spire is relatively lower than that of Callogaza sericata (see Simone and Cunha, 2006, Figures 41-48).
(Kira, 1959) from Japan, which also has a smaller shell, The shell has a relatively higher spire than the type
forming its terminal aperture at half the size of adult species andarelativelylowerspirethanCallogazasericata
C. colmani. The Japanese species also differs in details (Kara, 1959) fromJapan. Although the Japanese species is
C. S. Hickman, 2012 Page 61
cm
Figures 14-15. External anatomy ofCallogaza colmani new species, holotype (AMS 115689) and paratype 3 (AMS 115689b).
14. Right lateral view, 15. Oblique viewot head/foot. Abbreviations: apg, anterior pedal gland; el, cephalic lappet; cm, columellar
muscle; ct, ctenidium; e, eye and eyestalk; ef, epipodial flap; esu, epipodial sense organ; et, epipodial tentacle; f, foot (sole of
mesopodium); h,head; lul,left(inhalant) necklobe;op,operculum;me, mantleedge;p,propodium; ml, right(exhalant)necklobe;
sn, snout; st, snouttentacles; t, cephalictentacle.
more similar in the pigments present in the shell, they thereis noevidence of holes oropenings in the upraised,
are patterned differently, as in the arrangement ofwhite papillae on the foot ol Callogaza colmani.
splotches on thebase ofC. sericata. The Japanese species There is no information on the radula of other species
has asmallershell, formingaterminalaperture athalfthe ofCallogaza. The radula ofC. colmani is similar to that
size ofadult C. colmani. of Gaza superba (Dali, 1881) (Figure 11), although the
This is the first account ofthe soft parts ofCallogaza tooth bases in the central field are thinner and the cusps
,
and the major features link it clearly with Gaza. The are thinner and more denticulate. The large number of
large number of epipodial tentacles is a feature shared lateral teeth (>5 per half row) was a shared feature
with some species of Margarites Gray, 1847, and was a originally linking Gazini and Margaritini (Hickman and
significant factor in classifying Margaritini and Gazini as McLean, 1990; Hickman, 1996).
sister tribes by Hickman and McLean (1990). Isolated The rachidian and lateral teeth of a thin-shelled deep-
epipodial sense organs anteriortothe epipodialtentacles water species originally described as Margarites simbla
do occur in some species of Margarites although iso- Dali, 1913 have many features in common with the new
,
lated papillae also occur beneath the neck lobes in a species ofCallogaza and are illustrated here (Figure 13)
number of cantharidine gastropods (Hickman personal tocallattentiontotwoeastern Pacificspeciesthatcannot
observation). Series of“holes” or anterior “foot orifices” be allocated at this time. The other species, Margarites
illustrated in several species of Gaza (Simone and huloti Vilvens and Sellanes, 2006, was described as
Cunha, 2006) are identical in placement on the foot, but part of a Chilean methane seep biota. Both species are
Page 62 THE NAUTILUS, Vol. 126, No. 2
thin-shelled but lack gazid determinate growth features. lip and other on lowermost parietal wall and connected
Vilvens and Sellanes (2006) and Waren et al. (2011) to eolumellar callus. Thin, transparent shell layer of
comparedM. kuloti to two species described from meth- unidentified composition superimposed as secondary
ane seeps off Japan: Margarites njukyuensis Okutani, callus on underlying eolumellar and parietal callus and
Sasaki, and Tsuehida, 2000 and Margarites shinkai continuous across parietal wall. Final whorl sculpture
Okutani, Tsuehida, and Fukikura, 1992. However, both of consisting of 130 closely-spaced, very finely-incised spi-
the Japanese species have radulae with margaritid fea- ral lines crossed by fine closely-spaced eollabral growth
tures that include the shapes ofthe rachidian and lateral lines, visible only with magnification. Suture slightly
teeth, thepresenceofalateromarginalplate, andmarginal adpressed toprecedingwhorl throughout coiling.
teeth with base rows and cusp rows that correspond with
thebase andcusp rows oi the centraltooth complex. Remarks: The thickened and reflexed outer lip is a
unique shared feature of all species of Gazidae. It is
Type Material: Holotype: Australian Museum, Sydney accompanied by a descending suture immediately prior
A11M5S68911(5s6he8l9laan(sdhelfliguarnedd raandiumlaal)).. FFiigguurreedd ppaarraattyyppee 21:: ttiovefoorfmdaettieornmoifnattheegtreorwmtihn.alThliep.tBhionthpafrieeattaulreasndarceoilnudmiecla--
AMS 115689b (animal). Additional paratypes: AMS lar callus may also be terminal features, but younger
115689c-f (shells with preserved animals), Fisheries RA7 individualswillberequiredtodetermineifthisisthecase.
Karala Stn. K78-23-09, 6 November 1978. The genus is distinguished from Gaza and Callogaza
Dimensions: Holotype: height 17.4 mm, maximum by the absence ofan umbilicus by and relatively greater
width 23.3 mm. Figuredparatype: height 17.9 mm, max- shell height. Height exceeds width, and the generating
imum width 22.9 mm. curve is tangent to the axis of coiling, precluding the
presence of umbilical space. It is further distinguished
Type Locality: Off Point Danger, New South Wales, from Callogaza by larger adult size (>20 mm), lack of
Australia, 27°55-57' S, 154°03' E, 550 m. Point Danger pigmentation, and the absence both of axial sculpture
is not recognized as a place name by the Australian and any strong spiral elements or peripheral demarca-
Department ol Natural Resources, Division of National tion. Shells lack the lustrous sheen typical ofboth Gaza
Mapping. It is, however, on AdmiraltyCharts usedbythe and Callogaza. The suture is slightly adpressed to the
Kapala, and P. H. Colman (pers. comm., 2008) traces its preceding whorl in contrast to the impressed suture in
origin to 1770 when Captain James Cook gave the name species ofGaza, andthe aperture is less prosoeline.
of“MountWarning” to a prominent feature onshore and The shell apex is worn on both holotype and paratype,
“PointDanger”tothecorrespondingoffshorepointwhere obscuring the details of protoconch size and early
shoals lay. Cook further noted: “Point Danger is the teleoconch sculpture.
NSW
boundarypoint on the coastbetween and Qld.”
Etymology: an (Gr. without) + omphalos (Gr. umbili-
Distribution: Thebathymetricandgeographicdistribu- cus), recognizingthat there is neither an open umbilicus
tionsofthisspeciesareyettobedetermined,buttherecov- oran umbilicus thathas been sealed over by secretion of
eryol7livespecimensinasingledredgehaulsuggeststhat aterminal callus deposit.
itmaybelocallyabundant. ThesamehaulcontainedUiree
live specimens ofanother large-shelled vetigastropod, the Anomphalogaza moluccensis new species
calliotropidCalliotropisglypta(Watson, 1879). (Figures 16-21)
Etymology: Named in honor ol Philip H. Colman, Description: Same as forgenus (monotypic genus).
formerlyoftheAustralian Museum, Sydney, whowas on
the dredging expedition and called the material to the Remarks: The holotype and paratype were both col-
attention ol the author. lected as empty shells. Unlike many gazid species, the
GenusAnomphalogaza new genus apex of the shells is not perforated and the shells are
free of epi- and endobionts. However, the shell of the
Type Species: Anomphalogaza moluccensis new spe- paratype is corroded; and the exfoliation of outer shell
cies, by monotypy. has exposed the evidence of two distinct layers. Both
shells sustained and repaired episodes ofsublethal dam-
Description: Shell lacking umbilicus, shell height (up age to the growing margin ofthe aperture. On the holo-
to 29.2 mm) exceeding shell width (up to 22.1 mm). type there are six repaired breakages on the bodywhorl
Interior nacreous layer thickest, coveredbytwo distinct, and eight on the exposed portion of spire whorls. Both
unpigmented outer layers, No evidence of opalescent specimens repaired an irregular breakage along the
sheen from underlying nacreous layer. Nacreous layer, entire apertural margin immediately prior to secretion
aswellas outerlayers, thickenedand reHexed atterminal of the terminalapertural rim.
aperture. Terminal aperture descending. Nacreous pari-
etal callus divided into two portions, one on upper pari- Type Material: Holotype USNM 311367. Paratype
etal wall immediately below upper termination ofouter USNM 311367b. Both emptyshells.
C. S. Hickman, 2012 Page 63
Figures 16-21. Anomphalogaza moliiccensis newspecies. 16. Apertural, 17. Basal, and 18. Apicalviews ofthe holotype, USNM
311367, height = 29.2mm. 19. Apertural, 20. Basal, and21. Apical views ofparatype, USNM 311367a, height = 28.0 mm.
Dimensions: Holotype: Height 29.2 mm, maximum and Caribbean fauna (Clench and Abbott, 1943). Their
width 22. mm. Paratype: Height 28.0 mm, maximum relatively large shell sizes and local abundance (Quinn,
1
width 21.9 mm. 1979) have facilitated theiruse as models for understand-
ing taphonomie and paleoecologieal phenomena in deep-
Type Locality: U.S.FishCommission, R/VAlbatross,Sta- sea gastropods (Walker and Voight, 1994; Voight and
tion 5601. 13 November 1909. 01°13'10" N, 125°17'05" E. Walker, 1995). The Gaza Community was designated as
Molucca Sea Indonesia Celebes (Sulawesi). 765 Fathoms an example ofa deep-water community type with origins
(=1,399 m). Sand, Globigerina and pteropods. in the Eocene (Hickman, 1984b). Discoveries ofchemo-
Distribution: The genus and species are thus far syntheticallynourishedcommunities in the northern Gulf
known from only a single locality at greater depth than of Mexico (Kennicutt et al., 1985) suggest a potentially
any ofthe gazid taxa described to date and in a setting unconventionalcarbonsource lor these large gastropods.
that is more geologically remote and isolated. It is iso- Four aspects ol the morphology and biology ofthese
lated by its tectonic setting at the western edge the gastropods are reconsidered here: (1) the phenomenon
Molucca Sea Microplate, the only known site of active of determinate growth, (2) the high incidence of repair
collision between two facing Island Arcs. The geologic of sublethal shell damage, (3) the umbilicate condition,
complexity ofthis region is treated further in the discus- and (4) the nutritional carbon source.
sionbecause itis pertinenttounderstandingthe geologic
and evolutionaryhistoryof the deep-seafauna. Determinate Growth in Gazid Gastropods: Determi-
nate growthis manifestinthree morphological features of
gazid gastropods: (1) reflection and thickening of the
DISCUSSION
outerlip, (2) reflection ofthe columellarlip to form athin
BiologicalAnd Paleobiological Reassessments callus completely orpartially covering the umbilicus, and
(3) a descending suture. It is the only family-group
Gaza andCallogaza have been recognized formanyyears vetigastropod taxon in which all known species develop
as conspicuous elements ofthe tropical Western Atlantic these three features. The thickened and reflected lip was
Page 64 THE NAUTILUS, Vol. 126, No. 2
used as a diagnostic feature in proposal of the family- gastropods not only show high repair frequencies but
group name (Hickman and McLean, 1990). The thin, also that the shells of these species lack the typical
translucent, bubble-like callus is, likewise, a unique anti-predator adaptations (Walker and Voight, 1994;
derivedfeature ofthe genus Callogaza (Hickman, 1998). Harasewych, 2002). A study of repaired breakage in
In marine gastropods, determinate growth occurs pri- pleurotomariidgastropods reported “extraordinarilyhigh
marilyinsiphonatecaenogastropods andinshallow-water, level ofunsuccessful predation for all species examined”
tropical habitats (Vermeij and Signor, 1992). It is recog- (Harasewych, 2002). This is surprising because these
nized most often by a terminal elaboration of the aper- species have an uncalcified operculum, relatively thin
ture, which maybe thickened, reflected, orflaired. Other shell, and open umbilicus that should render them
signaturesofcessationofspiralgrowth incaenogastropods mechanically more vulnerable than taxa with robust
include the formation of a distinctive parietal callus that shells, no umbilicus, and a heavy calcareous operculum.
mayextendontothespireandachangeinthe directionof However, living pleurotomariids also appear to be well
spiral growth, where it is referred to as an “ascending defended chemicallyby a hypobranchial gland secretion
suture” (Vermeij and Signor, 1992). that is released in response to disturbance and shell
Although determinate growth has been considered damage (Harasewych, 2002). High shell repair frequen-
rare in the basal “archaeogastropod” groups (Vermeij cies were also reported in a study of species of Gaza
and Signor, 1992), there is increasing evidence oftermi- and large-shelled species of the calliotropid genus
nal features that do not occur earlier in ontogeny. In Bathybembix Crosse, 1893 (Walker andVoight, 1994).
contrast to siphonate caenogatropods, changes in direc-
tion ofspiral growth are typically recorded as a descend- The Umbilicate Condition in Gazid Gastropods: The
ing suture between the body whorl and penultimate terms used to describe the umbilicate condition in gas-
whorl. A descending suture immediately precedes the tropods are difficulttoapplyto gazidsbecause closure of
formation of the thickened terminal lip can be seen in an umbilical opening, il it occurs, is a thin reflected
both the new species of Callogaza and the new genus nacreous layer secreted at the cessation ofgrowth. The
Anomphalogaza. Inotherbasalgastropodcladesadescend- shell is phaneromphalus until growth ceases and never
ing suture occurs in some, but uot all, species. Ifthere is becomes partially or completely plugged in the sense of
no terminal modification ofthe lip, a descending suture hemiomphalous orcryptomphalous. Theterminal partial
mayaccompanyaslowingofgrowth inthe largestindivid- or complete sealing off of the umbilicus partially or
uals. Lor example, some species of Clanculus Montfort, completely hides its presence as an emptychamber.
1810haveadescendingsuturewithoutanyterminal mod- In tlie new genus Anomphalogaza, there simply is no
ification ofthe aperture (Hickman, personalobservation). umbilicus,andtheterminalcolumellarandparietalcalluses
In contrast, a descending suture is paired with a flaired are reflectedovershellonly: there is noopeningto sealoff.
and reflexed aperture in some species of deep-water The lack of an umbilical plug contributes to the light-
gastropods in the genus Calliotropis Seguenza, 1903 nessofthe shellandlowinvestmentincalciumcarbonate.
(Hickman, personal observation). The perforation of the apex in some species, rendering
The descending suture forces the spire of the active the umbilicus open at both ends, is permitted bythe lack
crawling animal upward, increasing the angle between offilling. The lackofumbilical fillinghas permitteduse of
the axis of coiling and the substrate. Lunctional signifi- the umbilicus ofGaza superba and Gaza olivacea Quinn,
cance of the change in coiling geometry is not known, 1981 by a polychaete that is alleged to create the apical
nor is the function ofterminal modification ofthe aper- perforation (Quinn, 1991; Voight andWalker, 1995).
ture. WalkerandVoight 1994) reportedhighshell repair
(
frequency in two species of Gaza in a study showing Nutritional Carbon Source of Gazid Gastropods:
that attempted predation is common in large-shelled Gaza and Callogaza have not been identifiedconclusively
mm
(>25 height) gastropods, although rare in small- as elements of chemosynthetieally nourished communi-
shelled species. Ifthe ability to repair apertural damage ties. However, Gaza superba and Gaza fischeri Dali,
decreases with age, formation of a thickened terminal 1889 are locally abundant on the upper slope in the Gulf
aperture may provide an adaptive advantage to repro- of Mexico in regions of confirmed methane and sulfide
ductively mature adults. Irregular breakages on the seepage (Kennicutt et al., 1985; Carney, 1994). Live new
shells ofGaza superba indicate that there was no termi- records of Gaza fischeri from the Louisiana slope are
nalthickening at the time the damage occurred. included in an account of seep and vent gastropods
(Waren and Rouchet, 1993). There is no evidence ofan
ShellRepair in Gazid Gastropods: High frequencyof enriched photosynthetically derived (detrital) carbon
shell repair in living and fossil marine gastropods serves source to support communities dominated by gazid spe-
as in indicator of predation pressure and of predator cies. However, the alternative possibility ofdiffuse seep-
ability to survive attempted predation (Vermeij, 1982). age sensu Nesbitt and Campbell, 2004) supporting
(
Studies ofshell repair frequencies on small-shelled gas- chemoautotrophic bacterial synthesis of organic carbon
tropods concluded that predation pressure was low in in and on the sediments is worth investigating. Possible
the deep sea (Vale and Rex, 1988, 1989). It is therefore sources ofenriched dietary carbon also include bacterial
surprising that later studies of large-shelled deep-sea degradation ofhydrocarbons in sediments (Brooks et al.,
C. S. Hickman, 2012 Page 65
1987). In this instance, the concept ofa seep community and longer geologic history (see Lee and McCabe, 1986).
is not synonymous with chemosymbiosis. It is, however, With the knowledge that active plate margins are sites ol
indicative ofan unconventionalcarbon source. venting and seepage fueling chemosynthetically based
The enlarged hindguts ofthese gastropods are packed communities, it is now possible to target sites that have
with sediment, and sedimentary grain coatings have never been sampled for ehemosymbiotie taxa in the
SW
been implicated as a significant source oi nutrition for waters ofSoutheastAsia andthe Pacific.
large deposit-feeding gastropods that selectively ingest
grains with the greatest surface area to volume ratio
(Hickman, 1981). The earliestoccurrences (late Eocene) FUTURE DIRECTIONS
of large-shelled calliotropid gastropods of the genus
Bathybembix are in a geological setting ofboth discrete New morphological and anatomical data from this
and diffuse methane seepage on an active continental report, combined with detailed anatomical data from a
margin (Hickman, 2003). new Brazilian species (Simone and Cunha, 2006) are
consistent with previous morphological inference of
gazid monophyly, regardless of rank and classification.
Biogeographic Reassessment The novel combination offeatures ofshell, radula, anat-
omy, nutrition, and ecology distinguish it from other
The new taxa described here call attention to a more vetigastropod family groups. However, the relation-
global biogeograpliic pattern and to extra-tropical occur- ships of family groups ofvetigastropods are still poorly
rences in the Western Pacific. Callogaza colmani is the resolved, and morphological data presented here do not
first representative of the family recognized from the address phylogenetic relationships. For the morpholo-
Australian plate with its Gondwanan origin and history. gist, the challenge lies in unmaskingconvergence.
Anomphalogaza moluccensis is the first gazid described Strong morphological convergence in deep-sea veti-
from the biogeographic region ofWallacea. Indonesia as gastropods is clearly related to deep-sea benthic ecology
political and modern geographic unithas been assembled and deposit-feeding (Hickman, 1981, 1984b, 2003). The
over the past55 millionyears from complextectonic evo- enlarged hindgut, expanded and tentacular oral disk
lution ofmajor plate boundaries and microplates. In the margin, and anteriolateral expansion of the foot also
Eocene, present day Sulawesi (although not emergent as occur in large, deposit-feeding seguenzioid gastropods
land) was situatedsouth ofBorneo andwest ofits present such as species of Bathybembix Crosse, 1893 and
location in eastern Indonesia (Hall, 2001). The type local- Calliotropis Seguenza, 1903, a genus that is unusually
ity for the new gazid genus and species is on the dis- abundant and speciose at bathyal depths throughout the
appearing western boundary of what was once a large world and especially in the Indo-Pacific (Vilvens, 2007).
sea. The ancient Molucca Sea has been squeezed Shells also have converged on visibility ol nacre through
and subducted by convergence ofthe Philippine Sea an extremely thin outer shell layer and terminal growth
Plate, the Australian Plate, and the Eurasian Plate featuresthatinclude flaringorthickeningol the terminal
(Widiwijayanti et ah, 2003). The disappearance of the aperture, a descending suture, and reflection ofthe col-
Molucca Sea has received considerable attention because umellar callus to partially or fully cover (but not fill) the
it is the only present-day example of active collision umbilicus (Hickman, personal observation).
between two facingvolcanic arc-trench systems. Subduc- Thinning ofthe shell and terminal growth features are
tion beneath Halmaheratothe east andbeneath Sulawesi also common convergent shell features in several deep-
to the west is consuming the last of the microplate water skeneilorm gastropod groups (Hickman, personal
(McCaffery et ah, 1980; Hall et ah, 1995; Hall, 2000). observation). In describing the enigmatic Australasian
The thick, deformed seafloor collision complex trapped familygroup Kaiparathini (under Margaritinae), Marshall
between north arm ofSulawesi and Halmaherais, at min- (1993), noted several anatomical similarities to Gaza
imum, only250kminwidth (McCaffreyetah, 1980). The superba. Kaiparathinids do not fit comfortably into exist-
potential marine biogeographic importance of this com- ingvetigastropod classification.
plex history is that the shrinking ocean basin in which The genus Margarites Gray, 1847 needs both morpho-
Anomphalogaza occurs will have disappeared in another logical and molecular work to identify taxa that belong
three millionyears (Hickman, 2009). elsewhere. More than 50 species have been assigned to
The northern Arm of Sulawesi, the Molucca Sea, and the genus. In addition to the deep-water species noted
Halmahera are situated at the northern edge ofthe bio- above as candidates for transfer to Gazidae, there are
geographic region of Wallacea in the region of least extinct deep-water species datingback to the Cretaceous.
distance between Wallaces Line and Lydekkers Line. Kaim et al. (2009) described Margarites sasakii from a
The sharp terrestrial biogeographic breaks that define Campanian cold seep site in northern Hokkaido, Japan,
Wallacea have been considered invisible to shallow indicating deep origins of vetigastropods in chemosyn-
marine taxa, although there are recent challenges that thetically based communities. Deep-water fossil species
suggest a “marine Wallaces line” (Barber et ah, 2000). are also described from Eocene cold-seep carbonates in
For the deep-water fauna, the concept of Wallacea Paleogene rocks in the Pacific Northwest (e.g. Squires
requires greaterattention to structural features, tectonics. and Goedert, 1991).
Page 66 THE NAUTILUS, Vol. 126, No. 2
ACKNOWLEDGMENTS
Hickman, C.S. 1984b. Composition, structure, ecology, and
evolution ofsix Cenozoie deep-water mollusk communi-
Thispaperispartofaprojectbegun in 1975todocument ties. JournalofPaleontology58: 1215-1234.
new taxa of deep-water vetigastropods. I am grateful to Hickman, C.S. 1996. Phylogeny and patterns of evolutionary
jerry Harasewych and the late joe Rosewater for their radiation in trochoidean gastropods. In: J.D. Taylor (ed.)
assistance and encouragement in the use ofmaterial from Origin and Evolutionary Radiation of the Mollusea.
the Smithsonian Institution and to Winston Ponder, Phil Oxford University Press, Oxford,pp. 177-198.
Colman, and Ian Loch oftheAustralian Museum, Sydney Hickman, C.S. 1998. Subfamily Margaritinae. In: PL. Beesley,
fgorrateafsuslisttoanJciemiQnuithnen,stBurduyceofMaArusshtarlall,iaanndmaDteariiaHle.rbIeratm, SGy.nJt.hBe.siRs.ossFaaunndaAo.fWAeulsltsral(iead.s.)V.Mo5,lluCsSeIa:ROthePuSbloiusthhienrgn:
and Jim McLean for earlier discussions of trochoidean Melbourne, Part B,viii,pp. 682-683.
Hickman,C.S.2003. EvidenceforabruptEoeene-Oligoeenemol-
morphology and relationships. Sally Walker and Geerat
Vermeij have contributed to my interest in Gaza and its lPursoctahnerof,aunEa.lA.chNaensgbiettinantdheL.PacIivfaincyN(oerdtsh.)weFstr.omIn:GrDe.eRn.-
allies through their fascination with unsuccessful preda- house to Icehouse: The Marine Eoeene-Oligoeene Transi-
tion, shell repair, and the phenomenon of determinate tion. Columbia UniversityPress, NewYork, pp. 71-87.
growth in gastropods. Discussions with SuzanneWilliams Hickman, C.S. 2009. Relict deep-water gastropods in a dis-
have been especially helpful in considering the alterna- appearing seaway. Program and Abstracts - American
tive approaches to vetigastropod taxonomy, phylogeny, Malaeologieal Society 75th Annual Meeting. Paleontologi-
and achievementofstabilityinclassification. I thank Jerry cal Research Institution SpecialPublication 37: 45.
Harasewych and an anonymous reviewer for helpful Hickman, C.S.andJ.H. McLean. 1990. Systematicrevisionand
suggestions for improvement of the manuscript. Marla suprageneric classification oftroehacean gastropods. Nat-
ural Histoiy Museum of Los Angeles County Science
Coppolino rendered the anatomicaldrawings.
Series35: 1-69.
Kaim, A., R.G. Jenkins, and Y. Ilikida. 2009. Gastropods from
Late Cretaceous Omagari and Yasukawa hydrocarbon
seep deposits in the Nakagawa area, Hokkaido, Japan.
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