Shell Aperture Research Articles

Reproduction of the vermetid gastropod Dendropoma maximum (Sowerby, 1825) in Moorea, French Polynesia

Vermetidae are sessile molluscs with tubular shells cemented to the substrate. Although they are common inhabitants of coral reefs and rocky shores, little is known about the basic biology of most species. Dendropoma maximum is the largest vermetid species and is common across its Indo-Pacific range. Here we report on a study of reproductive and morphological traits in D. maximum from the lagoon around Moorea, French Polynesia. Both body length and diameter of shell aperture (generally the only visible part of the animal in the field) were good predictors of body weight and this relationship did not differ between males and females. Shell apertural diameter is therefore a good index of body size in D. maximum. The sex ratio became increasingly dominated by females with increasing body size, which is suggestive of protandric hermaphroditism. Probability of brooding, the number and size of brooded egg capsules, and the number of embryos per capsule were all positively related to female size. Females released veliger larvae that lived without additional food for up to 10 days, but were observed to feed when offered cultured phytoplankton on the final day. This is the first direct observation of feeding by larvae in this genus, and a planktotrophic larval stage has implications for potential dispersal in D. maximum.

Relative Growth and Reproduction in Tunisian Populations ofHexaplex trunculuswith Contrasting Imposex Levels

The banded murex Hexaplex trunculus was sampled at Menzel Jemil and Bizerta Channel (Bizerta Lagoon, northern Tunisia) to study imposex, growth, and reproduction. Butyltin concentrations were analyzed in females from the 2 sampling sites using the gas chromatographic flame photometric detection technique. Results showed that the Bizerta Channel population was severely affected by imposex, which was confirmed by the high level of butyltins recorded in females from this site. Growth in shell width and shell weight was higher in Bizerta Channel, whereas growth in shell aperture and flesh weight was favored in Menzel Jemil. The assessment of reproductive activity, made by calculating fecundity and using 2 condition indices, showed that the Menzel Jemil population was reproductively more active.

Wax barrier system

A customizable cerumen guard for a hearing aid having a shell, a receiver, a receiver tube, and aperture in the shell communicating with the receiver tube, includes an insert insertable into the shell aperture, the insert having a chamber therein, a receiver aperture for communication with the receiver tube, an ear canal aperture communicating with the ear of the wearer; and a plurality of customizable, interchangeable caps covering the ear canal aperture. The cerumen guard may also have any of a number of customizable cerumen­trapping accessories that may be placed into the chamber.

Variability in the sculpture of the shell aperture of Ruthenica filograna (Rossmassler, 1836) (Gastropoda: Clausiliidae) in specimens from natural populations and from laboratory breeding

An analysis of variability in the sculpture of shell apertures was carried out for 1,087 specimens of Ruthenica filograna from 33 localities and for 20 laboratory-bred individuals reared from parents from a single locality. Nine patterns of aperture sculpture were distinguished. There are usually two kinds of sculpture: with one plica in the aperture being an extension of the inferior lamella, and without plicae in the aperture. Sporadically, the subcolumellar lamella may be connected with the lip of the aperture by a plica. Additional plicae occur in the aperture only rarely. All populations examined showed variations in the number and arrangement of plicae. The coefficient of variation in the number of plicae in the shell aperture ranged from 32.6% to 121.8% within localities. No consistent relationship was found between the geographical location and the shell sculpture pattern. Specimens bred in the laboratory developed shell apertures with a variety of sculptural patterns, including one present neither in the parents, nor in the population from which it came. This characteristic is probably phenotypically plastic. It cannot be used for taxonomic purposes, and it is suggested that great caution is needed before using similar characters in other species.

Influence of prior experience on shell selection by the white spotwrist hermit crab Pagurus criniticornis (Crustacea: Paguridae)

Individuals of Pagurus criniticornis in a free-choice situation were experimentally tested under different laboratory conditions. In order to assess the effect of recently occupied shells on the size- and type-preference by hermit crabs, individuals were held for 30 days under one of the following two conditions: (1) excess of shells and (2) absence of shells. The crabs were then allowed to select shells from a wide array of empty gastropod shells of the two most-occupied species, as observed previously in the field: Cerithium atratum and Morula nodulosa. Preferred shell type (species) and size (shell aperture width and length) were correlated with hermit-crab size. The crabs showed a strong (100%) preference for C. atratum shells, demonstrating that recent and past experience did not influence either shell-type or shell-size preferences in this pagurid.

Shell Utilization Pattern by the Hermit Crab Isocheles sawayai Forest and Saint Laurent, 1968 (Anomura, Diogenidae) from Margarita Island, Caribbean Sea, Venezuela

Isocheles sawayai is a hermit crab that is occasionally mentioned in the literature, and recently its distribution was extended to Venezuelan waters. Because no information on the biology and shell use patterns of this species inhabiting Caribbean waters is available, we provide the first information on shell occupation patterns of I. sawayai from Venezuela. Specimens were collected monthly from January to December 2000 along the sandy shore of Margarita Island, Venezuela. The 942 specimens collected showed different shell use patterns between the sexes and according to the reproductive condition of the females. The gastropods Leucozonia nassa (37.37%), Engoniophos unicinctus (25.37%), Nassarius vibex (4.88%), Melongena melongena (4.25%), and Stramonita haemastoma (3.82%) represent 76% of the total occupied shells. Of the total of 26 different shell species occupied by I. sawayai, males were found occupying 21, while females were found occupying all 26 shell species. In general, both sexes most frequently occupied L. nassa and E. unicinctus. However, the percentage of females occupying these shells was significantly higher than that of the males. Regression analyses showed the best correlation between crab size, shell aperture width, and shell internal volume. The current comparative investigation, in combination with other South Atlantic populations of I. sawayai, provided further evidence of shell use adaptation in hermit crabs from different areas, and increases our insight into shell use of shallow-water hermit crabs.

The evolutionary mechanism maintaining shell shape and molecular differentiation between two ecotypes of the dogwhelk Nucella lapillus

Two ecotypes of Nucella lapillus can occur allopatrically or sympatrically, according to different degrees of wave exposure and microhabitats, on rocky shores of NW Spain. We studied differences in shell size and shape in adults and families of shelled embryos captured in the wild, and molecular variation at 9 microsatellite loci and 4 mtDNA regions. Both adults and shelled embryos of the two ecotypes showed significant differences in size and shell-shape components (the most important being size of the shell aperture). Strong among-family variation suggests that shell-shape variation has an important genetic component, and the pattern of genetic differentiation was in agreement with traits being affected by divergent natural selection. No significant overall molecular differentiation was observed between the two ecotypes for mtDNA, although we found significant genetic structure at two microsatellite loci. Microsatellite differentiation between ecotypes at these two loci was larger in sympatry than in allopatry. These results and the comparison of tenacity suggest that the two forms are distinctly adapted to differences in shore level and degree of exposure to wave action.

How to recognize in situ fossil cephalopods: evidence from experiments with modern Nautilus

Field and flume experiments with modern Nautilus pompilius establish two prerequisites to recognize in situ preservation of fossil cephalopod shells (soft parts were within body chamber in situ at the time of fossilization): occurrence of the upper jaw within the body chamber and the position of jaws within the body chamber. Morphology of shells and jaws in modern and fossil nautiloids is so similar that these prerequisites can be applied for fossil nautiloids and provide implications for ammonoids. The upper jaws of Nautilus start to move at a water velocity of > 0.2 m/s, when the shells are reoriented with the aperture downstream; jaws are therefore unlikely to be secondarily deposited near the shell aperture by bottom currents. The lower jaws, moved at the velocity of > 0.1 m/s, can be deposited around the shell aperture by weak current (0.1–0.2 m/s in velocity), but never enter the inside of body chamber. Neither jaw is likely to be separately and selectively displaced from the inside of the body chamber through scavenging of the soft parts by burrowing infaunal animals. An upper jaw preserved inside the body chamber, together with a lower jaw, is thus a reliable indicator of in situ preservation; a sole lower jaw preserved around the shell aperture is likely to be secondarily deposited. Sedimentary structures inferring rapid burial events and jaw size are useful as additional evidence. Smaller jaws were more likely to be displaced from the body chamber by scavenging by infaunal animals after in situ burial, so that smaller jaws preserved within the body chamber suggest less scavenging. These findings are crucial to interpreting the taphonomic history and palaeo-ecology of fossil cephalopods.

Trade‐Offs between Force and Fit: Extreme Morphologies Associated with Feeding Behavior in Carabid Beetles

We explored how functional trade-offs in resource handling strategies are associated with the divergent morphology of predators. The malacophagous carabid Damaster blaptoides shows two extreme morphologies in the forebody; there is an elongate small-headed type and a stout large-headed type. A feeding experiment showed that the small-headed type obtained a high feeding performance on snails with a thick shell and a large aperture by penetrating the shell with its head. In contrast, the large-headed type showed a high feeding performance on snails that had a thin shell and a small aperture, and they ate these prey by crushing the shell. The large-headed, strong-jawed beetles are efficient at shell crushing but are ineffective at shell entry; the large mandibles and musculature that allow for shell crushing make the beetle's head too wide to penetrate shell apertures. On the other hand, small-headed, weak-jawed beetles crush poorly but can reach into shells for direct predation on snail bodies. These findings are hypothesized to be functional trade-offs between force and fit due to morphological constraints. This trade-off would be a primary mechanism affecting both resource handling ability in animals and phenotypic diversity in predators and prey.

PREDATOR-INDUCED MORPHOLOGICAL DEFENSES IN MARINE ZOOPLANKTON: A LARVAL CASE STUDY

While there are numerous reports of predator-induced morphological defenses for freshwater zooplankton, freshwater larvae, and benthic marine animals, a literature search revealed no reports of predator-induced morphological defenses for marine zooplankton. Rarity of predator-induced morphological defenses in marine zooplankton would imply a difference in predation risks compared to those experienced by freshwater organisms and benthic marine adults, whereas the presence of such plasticity in defenses would imply that risks are modified by developmental responses. This study reports a predator-induced change in defenses and vulnerability of a marine planktonic larva. Specifically, when reared in the presence of zoea larvae of Cancer spp., veliger larvae of the intertidal snail Littorina scutulata developed significantly smaller shell apertures and rounder shells than did cohort veligers reared in the absence of predator cues. Pairwise predation trials demonstrated that veligers reared with caged zoeas throughout development had greater survival than predator-naive veligers during short-term exposure to zoeas. The development of predator-induced morphological defenses by some marine larvae introduces a range of testable hypotheses on developmental plasticity that reduces vulnerability of planktonic larvae and other marine zooplankton to predators.

相模湾で採集されたシロヒメガキ（軟体動物；二枚貝網）の生態

Five specimens of Ostrea fluctigera Lamy, 1925 were collected from the Sagami Bay, adhering by their left valves to the lowest body whorl (near the aperture) of empty shells of several gastropod species, including those used by hermit crabs. In each case, the curved edge of the left valve precisely matched the curvature of the lowest body whorl of the snail shell, and both the left and right valves grew as an extension of the snail shell's aperture. The possibility of a mutualistic symbiosis between O. fluctigera and hermit crabs is discussed.

Shell utilization pattern of the hermit crab Clibanarius vittatus (Crustacea, Anomura) in an estuary at São Vicente, State of São Paulo, Brazil

We evaluated the gastropod shell utilization pattern of the hermit crab Clibanarius vittatus (Bosc, 1802) at Pescadores Beach in São Vicente, State of São Paulo, Brazil. Specimens were collected monthly from May 2001 through April 2003, in the intertidal zone at low tide. The crabs were weighed and their carapace shield length measured. All gastropod shells were identified and had their shell biometric parameters (total length and aperture length) measured (mm) and weighed (g). A total of 2,344 hermit crabs (644 males, 1,594 females, 45 ovigerous females and 61 individuals in intersex), using 13 species of gastropod shells, were collected. Stramonita haemastoma (Linnaeus, 1767), Cymatium parthenopeum (Von Salis, 1793) and Achatina fulica (Bowdich, 1822) comprised over 98% of all the shells. Male and intersex crabs were significantly larger than the females. This size difference strongly influenced the shell utilization pattern, principally in A. fulica, which has the largest shell size, that was only used by males and intersexual individuals of C. vittatus. Cymatium parthenopeum was the only shell species that showed a high determinant coefficient in all the biometric correlations evaluated. The high abundance of S. haemastoma shells and a strong correlation between crab size and shell aperture length established by a significant determination coefficient, indicated that C. vittatus uses this species as the principal resource for shell occupation at Pescadores Beach.

Usefulness of the opercular nucleus for inferring early development in neritimorph gastropods

The early ontogeny of gastropods (i.e., planktotrophic vs. nonplanktotrophic) may be inferable from the morphology of the protoconch in adult shells. The protoconch consists of both embryonic and larval shells in species with planktotrophic development; the embryonic shell forms in the intracapsular period and the succeeding larval shell gradually develops during the larval period. In nonplanktotrophic species, on the other hand, there is no additional growth of the larval shell and the protoconch consists exclusively of a relatively large embryonic shell formed prior to hatching. This "shell apex theory" has been applied to many species of shell-bearing gastropods, but biotic and abiotic erosion of the apex often prevents detailed examination of the protoconch and subsequent inferences about ontogeny. I examined the gastropod operculum to test its utility for predicting developmental mode, drawing on the Neritimorpha as model taxa. Most aquatic members of Neritimorpha were found to bear an operculum with a clearly demarcated nucleus; SEM observations reveal four types of nuclei, which correspond to different types of protoconch morphologies and observed ontogenies for the study species. The nucleus is secreted before metamorphosis, fits into the shell aperture of the larva, and reflects early ontogeny as morphology, as does the protoconch. Moreover, the apparently organic (rather than calcareous) composition of the nucleus makes it nearly invulnerable to erosion and very advantageous, compared to the protoconch, in this ecologically diverse group, whose habitats range from freshwater streams and mangrove swamps to rocky shores and deep-sea hydrothermal vents. The measurements of the nucleus are also valuable for taxonomic purposes, especially in the species identification of veliger larvae and juvenile snails. On the other hand, the opercular nuclei of the Caenogastropoda and Heterobranchia are often eroded away in adult individuals; even if present, the morphology of the nuclei does not seem to clearly reflect early ontogeny in those groups.

Reproductive behavior of intertidal hermit crabs (Decapoda, Anomura) in southeastern Brazil

The reproductive behavior of four intertidal hermit crab species [Clibanarius antillensis Stimpson, 1859, C. sclopetarius (Herbst, 1796), C. vittatus (Bosc, 1802), and Pagurus criniticornis (Dana, 1852)] was studied in São Sebastião Channel, southeastern Brazil. The overall behavior followed previous descriptions for Diogenid and Pagurid hermit crabs but some particular differences were recorded. Male to male agonistic encounters over females and guarding behavior were more common to C. sclopetarius, C. vittatus, and Pagurus criniticornis. During guarding, males clearly grasped females' chelipeds, eyestalks, and the margins of their shell apertures. This oblique guarding and, simultaneously, accessing behavior (OGAP) has never been described for hermit crabs and was more common to C. sclopetarius and C. vittatus. Pagurus criniticornis did not present the typical jerking behavior of pagurids. Multiple copulations between a single pair were recorded in all species while in only one occasion a female of C. vittatus was observed copulating with two males. In the post-copulatory behavior males held females for some time and, after that, they were left inactive and sometimes totally to partially buried in the substrate. In mating pairs of all species males were larger than females and two individuals (out of 23) of C. antillensis, one (out of 5) of C. sclopetarius and one (out of 3) of C. vittatus, which courted successfully as males fertilizing females' eggs, were demonstrated to be intersex, with both male and female gonopores.

Presence or absence of the shell aperture: a criterion to identify shell breakage induced by durophagy in Umbonium (Mollusca: Gastropoda: Trochidae)

The pattern of shell breakage in the Recent trochid gastropods Umbonium (Suchium) moniliferum (Lamarck) and U. (S.) giganteum (Lesson) was observed under durophagous predation by crabs and in tumbling experiments, and the results of these experiments were applied to recent population samples from the natural environment. The experiments were carried out in order to learn if the pattern of shell breakage by durophagy (shell crushing) is different from that induced by water currents and waves. After predation by the predatory crabs Calappa lophos (Herbst) and Portunus trituberculatus (Miers), shell apertures of U. (S.) moniliferum and U. (S.) giganteum were broken in a characteristic fashion. In contrast, shells tumbled with sand and artificial seawater rarely lost the apertural margins, although other parts of the shells were relatively severely abraded. These results suggest that a shell from the natural environment with a similarly broken apertural margin was probably attacked by a durophagous crab, and that water currents and waves are not agents that cause breakage of shell apertures. The results were then applied to samples of Recent U. (S.) moniliferum from Lake Hamana-ko and fossil U. (S.) costatum (Kiener) from the Pleistocene Jizodo Formation in Japan. Shells with broken apertural margins amounted to 60% of all dead empty shells in the sample of Recent U. (S.) moniliferum, and over 90% in the sample of Pleistocene U. (S.) costatum, suggesting that these shells were extensively preyed upon by durophagous crabs. Shell repair frequencies of Recent U. (S.) moniliferum, calculated as a percentage of individuals with one or more repair scars, were 24–55%. The high repair frequencies indicate that considerable numbers of U. (S.) moniliferum can escape from attacks by crabs. All the results suggest that shell breakage along the apertural margins of gastropods is a good indicator of durophagy and that broken apertures, as well as shell repairs, are a useful tool for the investigation of predatory-prey interaction.

A NEW EOCENE SPECIES OF THE HERMIT-CRAB SYMBIONT HIPPOPORIDRA (BRYOZOA) FROM THE OCALA LIMESTONE OF FLORIDA

COLONIAL METAZOANS that lived symbiotically with hermit-crabs create striking and distinctive fossils. Examples of such fossils recorded (Schindler and Portell, 1993) from Cenozoic deposits in Florida include the scleractinian coral Septastrea marylandica (Conrad, 1841) (see Darrell and Taylor, 1989), the hydrozoan Cystactinia ocalana Brooks, 1964, and the bryozoan Hippoporidra edax (Busk, 1859) [recorded as H. calcarea (Smitt) by Scolaro, 1970]. In all of these fossils, the symbiotic colony covers the entire external surface of a gastropod shell with a thick encrustation. Growth of the colony outwards from the shell aperture in the form of a helicospiral tube greatly extends the size of the chamber available for the hermit-crab occupant. In no known fossil examples of symbioses are the hermit-crabs preserved in situ. However, modern analogues, along with functional morphological considerations, provide good criteria for inferring that this peculiar colonial growth pattern occurred in response to the presence of a symbiotic hermit-crab, at least for examples within the Lower Jurassic-Recent range known for fossil hermit-crabs (see Walker, 1992; Taylor, 1994). Schindler and Portell (1993) reported a cheilostome referred to the genus Aimulosia from the Eocene Crystal River Formation (currently defined as the Upper Ocala Limestone, e.g., Oyen and Portell, 2001) as the oldest Florida example of a bryozoan that lived symbiotically with hermit-crabs. Subsequent research on this bryozoan has shown that it is an undescribed species belonging to another cheilostome genus, Hippoporidra Canu and Bassler, 1927. These new findings add to the significance of the Ocala Limestone fossil, here formally described as H. portelli n. sp., because it now becomes the oldest known example of the most widespread bryozoan genus that lives almost entirely symbiotically with hermit-crabs, extending the first appearance of the genus Hippoporidra back in time from the Early Miocene (Burdigalian) to the Late …

Hermit crab biocoenoses: a worldwide review of the diversity and natural history of hermit crab associates

The symbiotic associates of hermit crabs (excluding parasites and flora) are reviewed worldwide. The review includes species found on the shells occupied by hermit crabs (epibiotic species), species boring into these shells (endolithic species), species living within the lumen of the shell (either free-living or attached to the shell), species attached to the hermit crabs themselves, and hypersymbionts. In total over 550 invertebrates, from 16 phyla are found associated with over 180 species of hermit crabs. Among these associates, 114 appear to be obligate commensals of hermit crabs, 215 are facultative commensals, and 232 are incidental associates. The taxa exhibiting the highest number of associates are arthropods (126), polychaetes (105), and cnidarians (100). The communities of species associated with Dardanus arrosor, Paguristes eremita, Pagurus bernhardus, Pagurus cuanensis, and Pagurus longicarpus are the best studied and harbor the most diverse assemblages of species. While trends in biodiversity of hermit crab assemblages do not follow predicted patterns (e.g., hermit crabs within the Indo-West Pacific do not harbor more species than those from temperate regions), this is suggested to reflect a lack of sampling rather than a true representation of the number of associates. Hermit crabs date to at least the Cretaceous and provided a niche for a number of groups (e.g., hydractinians, bryozoans, polydorids), which were already associates of living gastropods. Apparently hermit crab shells initially supplied a substrate for settlement and then these symbiotic relationships were reinforced by enhanced feeding of symbionts through the activity of the hosts. Through their use and recycling of gastropods shells, hermit crabs are important allogenic ecosystem engineers in marine habitats from the intertidal to the deep sea. Hermit crabs benefit from some symbionts, particularly cnidarians and bryozoans, through extension of shell apertures (alleviating need to switch into new shells) and by providing protection from predators. However, hermit crabs are also negatively impacted (e.g., decreased reproductive success, increased predation) by some symbionts and a review of egg predators is provided. Thus, the symbiotic relationships between hermit crabs and many associates are difficult to characterize and often exhibit temporal changes depending on environmental and biological factors. Research on the biology of these symbionts and the costs/benefits of their associations with hermit crabs are analyzed. While some associates (e.g., Hydractinia spp.) have been studied in considerable detail, for most associations little is known in terms of the impacts of symbionts on hosts, and future experimental studies on the multitude of relationships are suggested.

Sanitation with sponge and plunger: western Atlantic slit-wormsnails (Mollusca: Caenogastropoda: Siliquariidae)

Siliquariid Tenagodus (synonym: Siliquaria) snails are obligatory sponge commensals, with uncoiling and laterally slitted shells embedded inside Demospongiae hosts, and shell apertures facing the outside allowing for respiratory and gill-filter-feeding activities. Live-collected animals observed in situ within hosts provide the first detailed functional morphological study of the group, and form the basis for systematic revision of the western Atlantic members of type genus Tenagodus (Siliquariidae, synonym: Tenagodidae). Three species are recognized. Overall anatomical features of wide-ranging Atlantic T. modestus (Dall, 1881) and T. squamatus (de Blainville, 1827) [ = T. anguillae Morch, 1861] are similar to those previously described for New Zealand Pyxipoma. A third species, Tenagodus barbadensis sp. nov., is described from Barbados, based on shell characters. The three species live embedded in a few species of halichondriid and thrombid sponges at depths ranging from c. 20 to several hundred metres and show several characters not previously documented for the family. These include a short compressed-S-shaped osphradium, an anal opening positioned in the posterior mantle cavity, and cuspidate inner marginal radular teeth. Presence of shell septa sealing earlier parts of the shell, first described in the early 1800s but subsequently disputed, was verified. Observations on living T. squamatus demonstrated the use of the large tight-fitting operculum in plunger-like fashion, flushing the mantle cavity and discharging waste material (including faeces from the posteriorly located anus) through the shell slit into the host sponge's aquiferous canal system. Uncoiling shells, shell and mantle slits, and specialized opercular, gill and gut morphology are interpreted as adaptive traits of the sessile mode of life embedded in sponge tissue. Actively maintained linkage between snail and sponge water-flow systems provides mutual benefits; these include the allowance for rapid defensive withdrawal and return-to-feeding position of the snail (by using the sponge canal system as a vent or reservoir for displaced water), sanitation of the mantle cavity (waste material can leave the snail through the shell slit at the posterior end of the mantle cavity, avoiding fouling of the gill-feeding system), and by providing increased water flow and, potentially, extra nutritional particles for the sponge (food and waste particles stemming from the snail's activity). The lectotypes selected herein are Serpula anguina Linnaeus, 1758, Tenagodus anguillae Morch, 1861, and Siliquaria modesta Dall, 1881. © 2004 The Linnean Society of London, Zoological Journal of the Linnean Society, 2004, 140, 307–333.

The edible West Indian “whelk” Cittarium pica (Gastropoda: Trochidae): Natural history with new observations

Cittarium pica (Linnaeus, 1758) is the third most important marine invertebrate species eaten by man in the West Indies. Information on it is widely scattered and is newly reviewed here, with original data, questions, and conclusions added. The animal has a relatively large shell and is easily collected, living intertidally and shallow subtidally on rocky shores. Its stocks are depleted at many places, large animals having been selectively removed by fishermen and others. There is only one living species of Cittarium, occurring in Bermuda, southern Florida, and in the greater West Indies. Its closest living relatives are all non-American, the only congener being the recently discovered C. maestratii Lozouet (2002) from the Oligocene of France. Thus the geographical and stratigraphic origins of the genus are still somewhat problematic. In Bermuda and southern Florida, the occurrence of C. pica alive is naturally sporadic. Sometimes sea surface temperatures are too low there for this tropical animal. The following topics are also reviewed: systematics, vernacular names, nomenclature, classification, anatomy and functional morphology, radulae, shell description, internal nacre, sizes and giants; shell strength, dextral coiling, and hermit crab occupancy; ecology and habitats, symbionts (unattached and attached), foods and feeding, reproduction, larval development and life history and movements, shell growth rates and longevity, predators, and escape responses; Pleistocene occurrences and historical extinctions in Bermuda and Florida; human introductions; also, human uses, including cookery, and possible tropical fish poisoning or ciguatera (caused by a toxic dinoflagellate).The most important new findings are: 1) That a shallowly shell-penetrating blue-green alga (Cyanophyta), probably Plectonema terebrans Bornet and Flahault, affecting only the white areas in the external color pattern (reported by Helen A. Randall, 1964), weakens these shell areas only and indirectly brings about differential erosion: the black, often zigzag stripes or marks on old shells become slightly higher in relief than the white areas. 2) Some aspects of multispiral operculum growth, visible externally only, are inferred from its morphology, but major questions remain. With growth, the operculum rotates as very many times as there are coils, and the growing edge is always in the same relative position, posterior, in the ever enlarging shell aperture. The operculum is attached on the inside by muscles arising postero-dorsally in the foot. The opercular muscle attachment and scar move, as they must, while the operculum grows and rotates very many times. How? 3) Occasionally, shells grow extra large in a very shallow, dead coral fringing reef habitat, not “deep”. The largest shell reliably reported is 137 mm wide and is from the Netherlands Antilles. Two from the Bahamas, the first with habitat data, are 132 and 126 mm wide. 4) Clouds of broadcast sperm were once mistaken for an “opaque liquid” causing “alarm” in nearby cittariums.None of these topics is addressed fully or at all by Fretter and Graham (1994) or Hickman (1998). Cittarium is shown to be primitive and in the mainstream of trochid evolution, having few if any noteworthy or remarkable biological specializations such as occur in some other trochids.Examples are given of extreme morphological and functional diversity in other taxa in the family Trochidae, comparing them with those in Cittarium. Trochids are suggested to have the widest adaptive radiation of any marine gastropod family (Hickman, 1996), yet primitive trochids such as Cittarium still exist and indeed thrive. Trochid adaptations tend, though, to be allopatric both as regards geography and ecology.

Borings in Cloudina Shells: Complex Predator-Prey Dynamics in the Terminal Neoproterozoic

Abstract Predation as an important driver of evolutionary change long has been assumed, despite difficulties to substantiate it with specific examples of predatory interaction, especially for the early Paleozoic diversification of animal life. This study corroborates the existence of shell-drilling predation in the uppermost Neoproterozoic of China. Nearly one-fifth of almost one hundred tubular shells of one of the earliest mineralized animals, Cloudina, are perforated by undoubted predatory borings 15–85 µm wide. By contrast, no specimens of co-occurring shells belonging to Sinotubulites were affected. The identity of the predator remains elusive, but variation in size of the borings suggests a predatory lifestyle throughout its growth, after it reached a minimum size. The relatively uniform distance of the borings from the shell apertures points to either control by the life orientation of the shells, such as the position of the sediment surface, or, more likely, an avoidance response by the predator t...