Gastropod Family Research Articles

The Glacidorbidae (Mollusca: Gastropoda: Heterobranchia) of Australia

The heterobranch gastropod family Glacidorbidae (?Pulmonata) is known only from temperate Australia and Chile. The Australian taxa are reviewed and three new genera, Benthodorbis, Striadorbis and Tasmodorbis are described based on differences in their shells, especially the protoconchs, and in their opercula and radulae. Nineteen species of Australian glacidorbids are recognised, all but four of them new. Of the four Australian species previously included in Glacidorbis, only two, G. hedleyi (Iredale) from New South Wales and Victoria, and G. occidentalis Bunn & Stoddart from south Western Australia, are retained in that genus. Eleven new species of Glacidorbis are described, seven from Tasmania (G. bicarinatus, G. catomus, G. atrophus, G. decoratus, G. costatus, G. tasmanicus and G. circulus), one (G. isolatus) from New South Wales, two (G. otwayensis and G. rusticus) from Victoria and one (G. troglodytes) from South Australia. Striadorbis contains the Tasmanian S. pedderi (Smith), and two new species, S. spiralis from western Victoria and S. janetae from Tasmania. Benthodorbis contains two species, both from old lakes in Tasmania; B. pawpela (Smith) from Great Lake and B. fultoni from Lake Sorell. Tasmodorbis contains a single species found in western Tasmania, T. punctatus, unique in having internal shell pores. Glacidorbis costatus is known only from Pulbeena Swamp in NW Tasmania and appears to be recently extinct, possibly as a result of draining of the swamp in the early part of this century. A cladistic analysis with the South American member of the family, Gondwanorbis, as the outgroup, supports the monophyly of the genera recognised.

Mechanisms underlying digenean-snail specificity: role of miracidial attachment and host plasma factors.

Digenetic trematodes usually show a high degree of specificity for their molluscan intermediate hosts. A panel of 4 digenean species (Echinostoma paraensei, E. trivolvis, Schistosoma mansoni, and Schistosomatium douthitti) and 5 snail species (Biomphalaria glabrata, Helisoma trivolvis, Lymnaea stagnalis, Stagnicola elodes, and Helix aspersa representing 3 gastropod families) was used to assess the relative contributions of miracidial behavior, host plasma osmolality, and host plasma factors in dictating specificity. Additional experiments were undertaken with a fifth digenean, Echinoparyphium sp. Expected patterns of compatibility were first confirmed; each parasite species produced patent infections in its known snail host, but not in the other snail species. One exception was S. douthitti, which unexpectedly did not infect L. stagnalis. As judged by direct observation and by noting their disappearance after exposure to snails, miracidia were generally less likely to attach to or penetrate incompatible than compatible hosts. However, over half of the miracidia of each parasite species attached to or attempted penetration of both compatible and incompatible hosts, suggesting that under the experimental conditions used, miracidial host location and attachment behaviors were not of overriding importance in dictating observed patterns of specificity. For each digenean species, the percentage of larvae that became immobile, rounded, showed tegumental damage, or died over a 6-hr interval in plasma of the various snails was assessed. In no case was plasma from a compatible host harmful to sporocysts or rediae. In contrast, in 8 of 16 (50%) incompatible combinations, snail plasma had a significant negative effect on sporocyst condition. In 4 of 12 (33%) incompatible combinations, plasma had a significant negative effect on rediae. In 9 of 10 combinations tested, lymnaeid plasma was toxic for the parasites of planorbid snails and in 2 of 4 combinations, planorbid plasma was toxic for the parasites of lymnaeid snails. Toxicity was not attributable to differences in plasma osmolality between snail species. The ability of plasma from incompatible snails to affect viability of both sporocysts and rediae was surprisingly strong, suggesting that humoral factors play a greater role in dictating patterns of digenean-snail specificity than previously appreciated.

A MOLECULAR PHYLOGENY OF NORTH AMERICAN PLEUROCERIDAE (GASTROPODA: CERITHIOIDEA) BASED ON MITOCHONDRIAL 16S rDNA SEQUENCES

The Pleuroceridae Fischer, 1885, is one of three freshwater gastropod families currently recognized in the superfamily Cerithioidea Ferussac, 1819 (Mollusca: Caenogastropoda Cox, 1960). Despite considerable literature justifying various proposed generic names of North American pleurocerids, no study has been conducted examining phylogenetic relationships of the recognized genera. In an effort to expand our understanding of evolutionary relationships of North American pleurocerid genrea, we examined a large portion of the mitochondrial 16S rRNA gene among 32 extant North American taxa. Multiple sequence alignment of the amplified region for our taxa resulted in a matrix consisting of 900 nucleotides including insertions and deletions. Based on analysis of nucleotide substitution patterns, we employed two approaches in our phylogenetic analysis: (1) all substitutions received equal weighting and (2) transversions were weighted 2X and 4X transitions to compensate for transition saturation among distantly related taxa. The molecular phylogeny based on the mitochondrial 16S rDNA sequences supports the monophyly of Pleurocera Rafinesque, 1819, Elimia H.&A. Adams, 1854, and Juga H.&A. Adams, 1854, but depicts the genera Lithasia Haldeman, 1840, and Leptoxis Rafinesque, 1819, as polyphyletic. The genus Pleurocera is sister to Elimia, which in turn is sister to a paraphyletic assemblage including representatives of Leptoxis, Lithasia, and the monotypic genus Io Lea, 1831. Juga, a genus restricted to west of the North American continental divide is the basal-most clade and is sister to all the aforementioned genera found east of the continental divide.

Latitudinal gradients of species richness in the deep-sea benthos of the North Atlantic.

Latitudinal species diversity gradients (LSDGs) in the Northern Hemisphere are the most well established biogeographic patterns on Earth. Despite long-standing interest in LSDGs as a central problem in ecology, their explanation remains uncertain. In terrestrial as well as coastal and pelagic marine ecosystems, these poleward declines in diversity typically have been represented and interpreted in terms of species richness, the number of coexisting species. Newly discovered LSDGs in the bathyal (500-4,000 m) benthos of the North Atlantic may help to resolve the underlying causes of these large-scale trends because the deep sea is such a physically distinct environment. However, a major problem in comparing surface and deep-sea LSDGs is that the latter have been measured differently, by using species diversity indices that are affected by both species richness and the evenness of relative abundance. Here, we demonstrate that deep-sea isopods, gastropods, and bivalves in the North Atlantic do exhibit poleward decreases in species richness, just as those found in other environments. A comprehensive systematic revision of the largest deep-sea gastropod family (Turridae) has provided a unique database on geographic distributions that is directly comparable to those used to document LSDGs in surface biotas. This taxon also shows a poleward decline in the number of species. Seasonal organic enrichment from sinking phytodetritus is the most plausible ecological explanation for deep-sea LSDGs and is the environmental factor most consistently associated with depressed diversity in a variety of bathyal habitats.

Revision of the gastropod family Pseudolividae from the Paleocene of West Greenland and Denmark

The Paleocene deposits on the Nuussuaq peninsula (West Greenland) contain three new species belonging to the family Pseudolividae de Gregorio, 1880. Popenoeum lacunosum sp. nov., Pseudoliva praetermissa sp. nov. and Fusulculus nanapullus sp. nov. are described. The species Fusulculus koeneni (Ravn, 1939) from the Paleocene (Selandian) of Denmark is revised, a lectotype is designated and new figures are published.Pseudoliva (Fusopsis) canalifera Ravn, 1939 is excluded from the Pseudolividae and Fusopsis is considered to be a subjective junior synonym of Suessionia Cossmann, 1889, and therefore reassigned to the family Buccinidae Rafinesque, 1815.

BATHYMETRIC PATTERNS OF BODY SIZE IN DEEP-SEA GASTROPODS.

The shift to smaller body size in marine invertebrates at the deep-sea threshold and size-depth clines within the deep-sea ecosystem are global biogeographic phenomena that remain poorly understood. We present the first standardized measurements of larval and adult size among ecologically and phylogenetically similar species across a broad and continuous depth range, using the largest family of deep-sea gastropods (the Turridae). Size at all life stages increases significantly with depth from the upper bathyal region to the abyssal plain. These consistent clines may result from selection favoring larger size at greater depths because of its metabolic and competitive advantages. The unusually small size of deep-sea mollusks, in general, may represent an independent evolutionary process that favors invasion by inshore taxa composed of small organisms.

The endemic molluscs of the Late Miocene Lake Pannon: their origin, evolution, and family‐level taxonomy

Long-lived lakes are often sites of spectacular endemic radiations. During the Oligocene to recent history of the Paratethys, large, long-lived (more than a million years) lakes with endemic faunas formed three times, in three different basins: the first in the Pannonian basin, the second in the Euxinian (Black Sea) basin, and the third in the Caspian basin. Because the Euxinian lake inherited much of the fauna of Lake Pannon, the three lakes together hosted two endemic radiations of molluscs. The most long-lived lake in the region was Lake Pannon, which persisted approximately seven million years from the late Middle Miocene to the Early Pliocene. Lake Pannon was formed by isolation from the sea. Changes in hydrological regime and/or water chemistry in addition to the relative lowstand which accompanied (or caused) the isolation almost completely exterminated the restricted marine fauna of the basin. A few highly euryhaline and marginal marine cardiids, dreissenids, and hydrobiids survived this environmental change. As in other fossil and extant long-lived lakes, the originally low-diversity fauna radiated into a high number of related endemic species (‘species flocks’) and genera in the expanding and ecologically vacated lake. Many originally freshwater taxa (unionids, sphaeriids, viviparids, valvatids, melanopsids, lymnaeids, planorbids) entered the lake as well, and some of them also gave rise to endemic clades. Evolution in both relict and freshwater immigrant groups led to the appearance of highly unusual shell shapes. Many lineages exhibit gradual morphological changes over one to several million years. More than 900 endemic mollusc species have been described from Lake Pannon, although this number includes junior synonyms, invalid species names, and highly similar chronospecies. Applying a conservative taxonomy, all these species belong to four bivalve and eight gastropod families. The high degree of endemism, however, is reflected by proposals of some authors to establish as many as five new families based on Lake Pannon endemics.

Calopia (Calopiidae), a new genus and family of estuarine gastropods (Caenogastropoda: Rissooidea) from Australia

A new family, Calopiidae is described for a new genus and four species, three of them new, from estuarine habitats in Australia. While similar to many rissooideans in having a simple, conical shell, Calopiidae can be distinguished from all other taxa by a unique combinatiom of apomorphic characters, including a simple operculum with calcareous-like opaque-white material on its inner surface. The long cephalic tentacles have complex ciliation, including long, distal compound cilia. The foot has an anterior cleft and the propodium lies dorsally behind the anterior edge of the foot. There is a short metapodial tentacle close to the posterior margin of the foot. The osphradium is longer than the poorly-developed ctenidium, the latter unusual in lacking skeletal rods. The intestine loops around the middle of the style sac, not at its anterior end as in most other caenogastropods, and the rectum forms tight S-shap coil on the penial roof. The testis is composed of a few large, long lobes and the prostate gland is triangular and closed . The large penis has a few large apocrine glands. The female system is unusual in lacking a seminal receptacle and in the oviduct gland being uniform throughout. The spawn consists of short rows of capsules and larvae hatch as swimming veligers. The relationships of the new family are assessed following a cladistic analysis, using 49 informative morphological characters, of similar rissooidean taxa. The strict consensus of the 40 shorlest trees shows Calopia as the sister of th four taxa in the analysis that are currently included in the Hydrobiidae. A replacement name, Calopia laseroni, is provided for Lucidestea perforata Laseron, 1956 a secondary homonym of Lucidestea perforata (Thiele, 1925).

HYDROPHOBIC LARVAL SHELLS: ANOTHER CHARACTER FOR HIGHER LEVEL SYSTEMATICS OF GASTROPODS

Higher level relationships within the Gastropoda are difficult to determine, in part due to the paucity of identified synapomorphic characters. Larval shell hydrophobicity may be a useful additional character for gastropod family systematics. A survey of 57 species indicates that larval shell hydrophobicity is common or ubiquitous in pyramidellids , opisthobranchs, and marine pulmonates but is unknown in patellogastropods, vetigastropods, and caenogastropods. The taxonomic distribution of hydrophobic larval shells is consistent with the hypothesis that it is a heterobranch synapomorphy. Unfortunately the condition in key 'lower' heterobranchs such as architectonicids and valvatoids is unknown.

Decline and contraction: The history of the relictual Gastropod family Pseudolividae

The neogastropod molluscan family Pseudolividae is one of several clades that have undergone a declinein diversity and a reduction in geographical distribution during the Cenozoic. After originating in the Late Cretaceous (Campanian), the group peaked in number of species during the Paleocene. A drop in diversity after the early Eocene was followed by successive contractions in geographical range at the end of the Eocene, during and at the end of the Miocene, and at the end of the Pliocene. Like several other gastropod groups with a similar history, the Pseudolividae are almost absent from the rich Indo-West Pacific region today. Relict groups with a significant Neogene record in Europe, by contrast, typically occur in the living biota mainly or exclusively in the central Indo-West Pacific. The decline and geographical contraction of the Pseudolividae occurred despite the post-Eocene evolution of two morphological innovations, the parietal tooth or rib at the adapical end of the inner lip, and lirae (spiral ribs) on the adaxial (inner) side of the outer lip.

The egg capsules of Bythinella austriaca (Frauenfeld, 1856) with observations on the veliger and embryonic shell

The world-wide distributed Hydrobiidae are the largest family of freshwater gastropods. The systematics of these small or minute gastropods remains unclear and little is known about their biology. This is particularly true of the genus Bythinella, minute inhabitants of springs in South and Central Europe. For instance, no data on their egg capsules can be found in the literature. In 1993-1994, while collecting material for another study, in St. Elias Spring, Eliasz6wka Valley, Krzeszowice, South Poland, I found egg capsules of Bythinella austnaca (Frauenfeld, 1856), containing eggs and embryos. The capsules, veligers and embryonic shells were found worth examining.

The roles of mass extinction and biotic interaction in large-scale replacements: a reexamination using the fossil record of stromboidean gastropods

The macroevolutionary processes underlying large-scale biotic replacements are still poorly understood. Opinion remains divided regarding the roles of mass extinction, biotic interaction, and environmental perturbations in these replacement events. Previous attempts to test replacement hypotheses have largely focused on taxonomic diversity patterns. Taxonomic data alone, however, provide little insight about ecological interactions and hence other approaches are needed to understand mechanics of biotic replacements. Here I propose a conceptual model of replacement based on predation-mediated biotic interactions, and attempt a test using analysis of the Cenozoic replacement of the gastropod family Aporrhaidae by a closely related group, the Strombidae.Taxonomic, morphologic, and geographic data analyzed in this study all suggest a replacement of aporrhaids by strombids following the end-Cretaceous mass extinction. While most of the taxonomic replacement was associated with a mass extinction, some replacement also occurred during background times and was mediated by higher origination rates in strombids rather than by higher extinction rates in aporrhaids. Morphologically, the replacement was largely confined to the portion of the morphospace unaffected by the end-Cretaceous extinction. At a global scale, the geographic overlap between the two groups declined through the Cenozoic, reflecting increasing restriction of aporrhaids to colder, temperate waters while strombids flourished in the tropics. However, at a finer geographic scale a more mosaic pattern of replacement is evident and coincides with Eocene and Oligocene climatic fluctuations.The results of this study suggest that mass extinction, long-term biotic interaction, and environmental change can all play significant roles in biotic replacements. Since the relative importance of each factor would vary from one event to another, an understanding of the general nature of large-scale biotic replacements requires a knowledge of the relative intensities of each of these processes.

The promotion and prevention of recoiling in a maximally snaillike vermetid gastropod: a case study for the centenary of Dollo's Law

The Neogene speciesPetaloconchus sculpturatuspresents a contradiction in terms, for it grows whorl “packages” of nearly perfect regularity, but ranks within the most geometrically irregular family of uncoiled gastropods, the Vermetidae. We perform a first biometric study of vermetids (only possible because sufficient regularity of growth permits us to number and identify whorls) to specify and characterize the factors on both sides of this “exquisite tension” between promotion and prevention of recoiling. Promoting factors include the older phyletic heritage of preserved dextral coiling, and the more immediate vermetid (or specifically petaloconchid) features of growth toward open spaces (where regular coiling might proceed in an unimpeded fashion); radular excision of discordant feeding tubes with shaping of the resulting scar so that growth may proceed in conformity with previous whorls; and locking of subsequent whorls upon a keel formed by longitudinal bead-rows of the previous whorl. Preventing factors include prominent phyletic heritage of all vermetids—maximal early irregularity enjoined by discordance between larval and subsequent growth (with teleoconch wrapping itself around the protoconch), thus precluding an ordered substrate to act as a foundation for regular whorl “packages” of intermediary growth—and a set of features specific to this lineage and acting as geometric constraints. In this category, we particularly document the exceedingly low rate of whorl expansion and the consequently wide umbilical space that produces a shell akin to winding a cylindrical coil of narrow-diameter rope around the periphery of a wide circular platform. This complex combination of promoting and preventing factors produces a shell that is tantalizingly close to fully regular, but cannot truly reattain this previous phyletic state—thus providing a fine example of Dollo's Law at the centenary of his formation of irreversibility.

New records, species, genera, and a new family of gastropods from hydrothermal vents and hydrocarbon seeps*

More than 100 species of gastropods from vent and seep localities around the world are reviewed, based on literature information and new material.The following new taxa are described (localities with parentheses, systematic position within brackets): Cantrainea macleani sp.n. (Louisiana Slope) [Turbinidae]; Fucaria striata gen. et sp.n. (Juan de Fuca Ridge area), Vetuloniaphalcata sp.n. (North Fiji Basin) [both Trochidae]; Protolira valvatoides gen. et sp.n. (Mid‐Atlantic Ridge) [Skeneidae]; Ventsia tricarinata gen. et sp.n. (Lau Basin), Bruceiella globulus gen. et sp.n. (Lau Basin) [both tentatively in Skeneidae]; Melanodrymia brightae sp.n. (Juan de Fuca Ridge area), Pachydermia sculpta sp.n. (Lau Basin), Planorbidella gen.n., P. depressa sp.n. (Lau Basin), Ctenopelta porifera gen. et sp.n. (EPR 13°N)[Peltospiridae]; Helicrenion reticulatum gen. et sp.n. (Lau Basin), Lepfogyra inflata sp.n. (Lau Basin) [families unknown]; Desbruyeresia spinosa gen. et sp.n. (Lau Basin), D. cancellata sp.n.(Lau Basin), D. melanioides sp.n. (Lau Basin), Provanna buccinoides sp.n. (Lau Basin) [Provannidae]; Hyalogyra vitrinelloides sp.n. (Lau Basin), Hyalogyrina grasslei s p a (Guaymas Basin)[Hyalogyrinidae fam. n.], Xylodiscula major sp.n. (North Fiji Basin) [Xylodisculidae].The external morphology of the soft parts [for Ifremeria and Alviniconcha (Provannidae) also the anatomy] is described for most of the taxa involved.Some features in the biology and distribution of the gastropod fauna are discussed. About half the fauna consists of species belonging to families or superfamilies endemic to this environment. One‐fifth of the remaining species belong to taxa normally associated with biogenic substrates in the deep sea. Alviniconcha hessleri has previously been shown to harbour chemosynthetic bacteria in the gill; Ifremeria nautilei is here confirmed to do the same. Ctenopelta porifera, and Hirtopelta hirta are suspected to have such bacteria because of reduction of the alimentary system.

Levels of selection and macroevolutionary patterns in the turritellid gastropods

This analysis examines the evolution of the greater diversity of species with non-planktonic larval types relative to species with planktonic larval types in the turritellid gastropods. This sort of trend has been documented in both the fossil and recent biota of several gastropod families. Two mechanisms for generating diversity gradients in larval types have been proposed in the literature. The first, species selection, focuses on the population biology of larval types. The second proposes that factors in development that are mediated by organismal adaptation are responsible. Turritellids have been cited as a classic example of species selection. In order to examine the relevance of these two proposed mechanisms, a phylogenetic analysis of the turritellids using molecular sequence data was performed to determine the evolution of larval types in this clade. The resultant phylogeny suggests that species selection is not the only process driving the trend toward increasing numbers of non-planktonic species through time. Developmental processes, apart from those involving organismal adaptation (except in the trivial sense), are implicated as playing a role in this trend. In particular, these processes may involve changes in the timing of germ-line sequestration in organisms. Germ-line sequestration governs how accessible organisms are to heritable variation during ontogeny. Embryological evidence from gastropods suggests that non-planktonic species have early germ-line sequestration relative to planktonic species, making them more resistant to developmental change. Thus, non-planktonic lineages will only rarely revert to a planktonic larval mode.

The nonmarine mollusks of the Late Oligocene–Early Miocene Cabbage Patch fauna of western Montana. II. Terrestrial gastropod families other than Pupillidae (Pulmonata: Stylommatophora)

The remaining terrestrial gastropod fauna of the late Oligocene–early Miocene Cabbage Patch beds of western Montana is composed of nine new species, all from extant genera now occurring in the western United States: Vallonia berryi, [Succineidae] montana, Nesovitrea pulchra, Deroceras securis, D. mahiz, Punctum alveus, Polygyroidea montivaga, Oreohelix brandi, and Monadenia? n. sp. A, which is described from neanic material. All except the Monadenia? represent first occurrences of the respective genus in North America. The terrestrial fauna suggests that climatic and environmental conditions during the late Oligocene–early Miocene interval must have been very similar to those of the present. Two sizes of gastropod eggs, attributed to P. montivaga and V. berryi, were found at one locality. Monadenia? n. sp. A is of limited use, due to rarity, as an index fossil for the upper Cabbage Patch beds.

Evolutionary history of Aporrhaidae (Gastropoda, Mollusca)

The Aporrhaidae is an important family of marine gastropods whose members are characterized by an expanded apertural lip. A phylogenetic analysis of this clade confirmed its monophyly although a few of the constituent genera, as presently defined, are polyphyletic. Stage-level diversity data for the Northern Hemisphere genera gathered through fieldwork, visits to museum collections and from the literature indicate an initial radiation of this clade during the middle Jurassic. This radiation produced 9 genera by the end of Callovian. Similar levels of generic diversity were maintained throughout latest Jurassic and the earliest Cretaceous. During the Jurassic the aporrhaids appear to have been geographically restricted to Europe and Africa. However, given the paucity of Jurassic marine sediments on most continents, this distribution is probably biased although absences in Japan and North America are probably genuine. The later part of the early Cretaceous history of this group is characterized by a major faunal turnover which resulted in the extinction of over 70% of the Jurassic genera and the evolution of at least 10 new Cretaceous genera. The group reached its highest diversity during the Albian, followed by a slight decline during the Cenomanian. This diversity peak is at least partially attributable to the exceptional quality of preservation during the Albian which is unsurpassed in any Jurassic or Cretaceous stages except the Maastrichtian. The average diversity for the rest of the Cretaceous stages remained around 12 genera and by late Cretaceous the group achieved a global geographic distribution. The aporrhaids suffered a severe setback during the Maastrichtian when at least 75% of the genera went extinct. The stratigraphic data presently available does not provide enough resolution to determine whether this extinction coincided precisely with the K-T event. At the generic level this extinction does not seem to exhibit any selectivity based on geographic range. Of the three end-Cretaceous survivors, Drepanocheilus and Arrhoges were widespread geographically while the third, Aporrhais had a restricted distribution. Similarly the taxa that perished included both endemic genera and widespread ones like Quadrinervus. The Cenozoic history of the clade is characterized by very low levels of generic diversity and restricted geographic distribution with only two extant genera.From a macroevolutionary perspective, the late Neocomian turnover as well as the Maastrichtian extinction of aporrhaid genera are particularly interesting. The first event gave rise to a number of distinctive morphologies and coincided with the radiation of various groups of durophagous predators such as decapod crustaceans as well as with the rise of the carnivorous gastropods. The nature and timing of this change suggests that it could be a part of the broader Cretaceous faunal reorganization commonly known as the “Mesozoic marine revolution” (Vermeij, 1977). The end-Cretaceous event is interesting for its magnitude as well as its consequences. The aporrhaids maintained a remarkably stable generic diversity level from mid Jurassic to late Cretaceous, but never recovered from the Maastrichtian extinction. This pattern is in direct contrast to that exhibited by the sister group of Aporrhaidae, the Strombidae. The strombids exhibit extremely low generic diversity and restricted geographic distribution during the Cretaceous but radiated rapidly during the early Cenozoic. Such reciprocal diversity trends, combined with close phylogenetic relationship and functional similarity of the two groups as well as the presence of morphologic convergence, suggests extinction induced replacement and seems to be consistent with models proposed by, among others, Hallam (1987) and Rosenzweig & McCord (1991).

Morphological evolution of the Muricinae

The Muricidae constitute a taxonomically and morphologically diverse family of marine gastropods. The subfamily Muricinae is the largest in the family with over 180 Recent species recognized. Modern representatives typically are strongly sculptured and possess pronounced axial thickenings (varices) and varical spines. Early fossil representatives of the subfamily generally do not display the strong ornamentation that is characteristic of more modern forms. A study of Recent and fossil muricines in museum collections was made in order to document quantitatively the morphological evolution of this group. Morphometric data were obtained from oriented photographs, X- radiographs and actual specimens. These data were supplemented with limited measurements made from published plates. A preliminary analysis of these data has revealed the following:1. Neogene and Recent representatives are significantly more ornamented than those of the Cretaceous and Paleogene. Neogene and Recent forms typically have thicker varices and a greater number of well developed varical spines. The diversity of varix and spine morphologies also increases through time. Intervarical nodes also become more developed during the Neogene. A less pronounced trend towards increased spiral ornamentation is also indicated. Similar patterns are observed in both Europe and the western Atlantic and a preliminary analysis of Indo - Pacific fossil taxa suggests that the trend exists in this region as well.2. Although the appearance and diversification of higher taxa contributes to the above pattern (eg. Chicoreus, Murex), similar patterns are also observed within previously existing taxa.3. Elongated siphonal canals become more prevalent in the Neogene, although this pattern is largely the result of the diversification of new higher taxa (eg. Murex, Haustellum, Chicoreus (Siratus)).4. The range of gross shell morphologies described by Raup's coiling parameters increases during the evolution of the subfamily. Taxa with relatively high rates of whorl translation and relatively high whorl expansion rates appear later in the history of the group. However, at the subfamilial level, no obvious directional trend exists and this pattern may be explained as an increase in morphological variance. Nevertheless, the possibility that this pattern is the result of a number of independent unidirectional trends at a lower taxonomic level can not yet be discounted.5. Mean shell size within the family increases during the Cenozoic.6. The Miocene appears to be an interval of increased morphological and taxonomic diversification.Although the function of the diverse sculpture expressed in muricids remains poorly understood, features such as thick varices, spines and spiral ribbing are known to play a role in resisting durophagous predators. Increased size has also been implicated as a means of avoiding predation. It is likely that some varices and spines perform other functions as well and there are indeed morphologies within the Muricidae that do not comfortably fit an anti - predation interpretation. However, the directional patterns of morphological change observed in the Muricinae are broadly consistent with an “arms - race” scenario and strongly suggest that durophagous predation was an important driving force in the morphological evolution of this subfamily.

Paleoenvironmental control of species distributions in Neogene invertebrate taxa of the Dominican Republic

Neogene deposits of the northern Dominican Republic contain a diverse fossil assemblage that is especially rich in corals and mollusks. To see if faunal change was concordant or discordant within and among taxa and decipher factors controlling distributions, we compared distributions of coral communities, the gastropod families Strombidae and Marginellidae, and the bivalve family Corbulidae. We also incorporated published ranges for the Cardiidae (Vokes, 1989), Cancellariidae (Jung and Petit, 1990), and the columbellid genus Strombina (Jung, 1986).First and last appearances of individual mollusk species were diachronous among sections. Within the sections, however, first and last appearances of mollusk species tended to coincide. Concordance of species ranges could be caused by unconformities or faults, be an artifact of sampling, or indicate similar responses by species to environmental changes. Neither stratigraphic gaps nor faults appear to correspond to concordant first or last appearances. Although the absence of mollusk taxa generally corresponds to less intense sampling, sampling intensity is highly correlated with the presence of macrofossils and therefore, taxa absence is probably real. First and last appearances do coincide with paleoenvironmental changes such as rapid deepening, introduction of marine conditions, increased intensity of erosional bottom currents, and changes from reefal to sand flat facies.Comparisons among taxa also helped elucidate other distributions patterns. For instance, comparing coral communities to strombid ranges showed that strombid diversity increased in grass flats (inhabited by free living corals) and reefal deposits, indicating similar ecologic preferences to many modern strombid species. Using the coral fauna to distinguish a grass flat community from other shallow marine facies also helped explain corbulid abundances as environmentally induced, with lower numbers in grass flat deposits.Simultaneous comparison of species distributions within diverse taxa can help explain the nature of species occurrences. For several mollusk taxa from the Neogene of the Dominican Republic, the general correspondence in distribution patterns across taxa indicates that paleoenvironmental conditions were controlling species distributions.

Protamines in prosobranchian gastropods (mollusca) vary with different modes of reproduction

AbstractWe have studied the protamines from different families of prosobranch gastropods. In those with external fertilization we find a simple pattern of sperm nuclear basic proteins, consisting of one major protamine. This protamine has between 75 and 105 amino acid residues in the ten species of the order Archaeogastropoda that we have examined. In six species of the order Patellogastropoda (Kozloff, Marine Invertebrates of the Pacific Northwest, Univ. of Wash. Press, Seattle, pp. 193–232, 1987), the protamine‐like component contains 220 ± 10 amino acid residues. However, the protamines from the archaeogastropod Monodonta turbinata and the patellogastropod Patella cerulea show a very similar amino acid composition. Cytochemically, four species of archaeogastropods and three species of patellogastropods show intermediate type 3 sperm basic proteins in the classification scheme of Bloch (Genetics 61:93–111, 1969; Handbook of Genetics, Plenum, New York, pp. 136–167, 1976). The sperm basic protein profile in six internally fertilizing species of the orders Mesogastropoda and Neogastropoda is more complex since several protamine bands are found. In all cases the major protamines have high electrophoretic mobilities and the number of amino acid residues is estimated to be from 40 to 60. The combined set of major protamines in the mesogastropod Littorina neritoides and the neogastropod Murex brandaris display a similar amino acid composition that differs significantly from that in the externally fertilizing gastropods. In one mesogastropod and three neogastropod species cytochemical staining indicates the possible presence of type 2 stable protamines. Protamines from a neogastropod have a capacity for compacting DNA that is similar to that of an externally fertilizing archaeogastropod. We propose that changes in protamine features amongst different prosobranch gastropods are correlated with changes in nuclear condensation patterns and the fertilization biology of these mollusks.