Juvenile Shell Research Articles

The morphology of the larval and juvenile shell of Pododesmus macrochisma (Deshayes, 1839) (Bivalvia: Anomiidae)

For the first time the data on the morphology of the larval and early juvenile shell of Pododesmus macrochisma (Deshayes, 1839), which is the only species of the Anomiidae family that inhabits the Peter the Great Bay, is given. The basic attribution characters of larval shell of this species at the veliconcha stage are the absence of the eye, the dark color of the shell, a shell height: length ratio that is nearly one, and the presence of four to five denticles at each side of the provinculum. A description of the early juvenile shell is given. The results of the study can be used to identify larvae in the plankton and early settled juveniles.

사육 수온이 코끼리조개 Panopea japonica (A. Adams, 1850) 치패의 성장과 생존에 미치는 영향

ABSTRACT This study was performed to determine the effect of water temperature condition on survival rate and growth of juvenile geoduck ( Panopea japonica ). Panopea japonica juveniles were bred for 6 weeks at 12, 15, 18, 21, 24 and 27℃ on incubator. Juveniles median lethal times (LT50) were 29 hours in 27℃, 14.5 day in 24℃, 37.4 day in 21℃. Survival rate of water temperature 12, 15 and 18℃ showed a high survival rate in 95.0%, 95.0% and 93.3% at 6 weeks. As a result of culturing for 6 weeks at 12, 15, 18, 21 and 24℃, a daily growth of shell length and total weight was 0.10 mm, 0.12 mm, 0.13 mm, 0.16 mm and 0.14 mm, and 2.21 mg, 2.65 mg, 2.84 mg, 3.13 mg and 2.93 mg. Juvenile shell length and total weight have significantly increased at 15-21℃. However, mortality rate has significantly increased at more than 21℃. As a result, appropriate water temperature for juveniles culturing considered 15-18℃.Key words: Juvenile geoduck, Panopea japonica , Culture, Water temperature, Median lethal time

Larval and post-larval growth, spat production and off-bottom cultivation of the smooth venus clam Chionista fluctifraga

Harvesting practices of the clam Chionista fluctifraga show a decline in commercial size and densities, but no strategies have been developed to maintain clam beds. Aquaculture represents an alternative for preserving this resource. Adult clams from commercial grounds were used as broodstock. Conditioning, induction of spawning, cultivation of larvae, settlement of eyed larvae and nursing of postlarvae were performed in the hatchery for producing spat. Larvae and postlarvae were used to measure increase in shell height and data were fitted to exponential growth models. Spat were placed in floating trays and maintained in off-bottom cultivation for 9 months. Samples of clams and tissues were collected monthly to measure absolute growth, shell height increase and a condition index. Larvae, postlarvae and juveniles showed exponential growth patterns. Mean shell height increased about 0.030 mm day−1 during larval and post-larval stages and 0.049 mm day−1 during field cultivation. Pediveligers (height 215 ± 83 μm) entered metamorphosis at days 9–13 after fertilization, and postlarvae reached 3011.7 ± 325.5 μm (height) at day 60. After field cultivation, survival was about 95%; juvenile shell height was 20.6 ± 2.2 mm, and total weight was 5.3 ± 0.7 g. Growth rates were superior to natural conditions and the condition index was high throughout the study. Our results show that spat of C. fluctifraga can be produced in the hatchery, and that field production can be maintained in off-bottom trays until reaching commercial size. Aquaculture activities for this species need to be established and evaluated.

Comparative Shell Microstructure of Two Species of Tropical Laternulid Bivalves from Kungkrabaen Bay, Thailand with After-Thoughts on Laternulid Taxonomy

Abstract: The anomalodesmatan family Laternulidae represents a group of bivalves with a very few well-known taxa and many more poorly known taxa. Laternula rostrata (G. B. Sowerby, 1839) and L. anatina (Linnaeus, 1758) occur in close proximity to each other in and along the margins of mangroves of Kungkrabaen Bay, Thailand. Laternula rostrata resides in soft to sandy sediments often within the interstices of mangrove roots located in more open portions of the mangrove mud flat. Laternula anatina lives deeper in the mangrove in more protected environs. Laternula anatina is a smaller bivalve that has a variable shell outline, sometimes a wrinkled shell appearance, thicker periostracum, and frequently extensive umbonal erosion. Both species have high concentrations of external shell spinules anteriorly and closer to the umbos (i.e., in juvenile shell) reflecting functionality in retaining an infaunal position. The larger L. rostrata is thinner shelled and more fragile; has more distinct and longer shell spin...

Shell growth, microstructure and composition over the development cycle of the European abalone Haliotis tuberculata

The shell of the European abalone Haliotis tuberculata is a model for studying mechanisms of mollusc shell formation, but the early steps of shell formation and calcification remain poorly documented. The microstructure and the mineralogical and geochemical composition of larval and juvenile shells were investigated by scanning electron microscopy, infrared spectroscopy and ion microprobe analyses (NanoSIMS). Analyses were performed on shells obtained from controlled fertilisations at the hatchery France-Haliotis (Plouguerneau, France) in July 2009 and 2010 using abalone from Roscoff. Shell cross sections revealed the microstructural arrangement of the developing shell, showing progressive biomineral organisation into two differentiated layers, i.e. the outer granular and the internal nacreous layer. Infrared analysis confirmed that the European abalone shell, at every stage of development, was mostly composed of CaCO3 in the form of aragonite. Variations in trace element composition, i.e. Sr/Ca, were measured in the different stages and correlated with micro-structural changes in the shells. Experimental manganese labelling of live abalones produced cathodoluminescence marks in the growing shell sections. The increase in shell thickness can be used to determine the growth rate of an early adult abalone shell.

Stable isotope data (δ18O, δ13C) of the ammonite genus Simbirskites — implications for habitat reconstructions of extinct cephalopods

The accurate habitats of the extinct ammonites and belemnites are largely unknown. Most ammonites are thought to have had a pelagic lifestyle, while belemnites are often considered to have dwelled in deeper, colder waters. Stable isotope analysis (δ18O, δ13C) provides a useful method to reconstruct the habitats of these two groups of extinct cephalopods, but is at the same time limited by various unknowns, including the isotopic composition of the past seawater, ‘vital’ effects and diagenesis.In this paper, stable isotope data from 12 ammonite shells (Simbirskites spp.) from the upper Hauterivian of the Lower Saxony Basin (northwest Germany) are presented. Ontogenetic isotope profiles have been obtained from six of these shells in order to reconstruct habitat changes during their lifetime. These new ammonite data are combined with published stable isotope data from belemnites (Hibolithes jaculoides) and TEX86 palaeotemperature-estimates from the same section.The combination of isochronous ammonite and belemnite stable isotope data shows that the resulting values of both groups go along with each other. Calculated palaeotemperatures of the two groups differ by 5–10°C, with belemnites always showing the colder temperatures. All juvenile shells show an increase of the δ13Camm to more positive values throughout their ontogeny; they are stable in an adult shell-fragment. The incorporation of carbon isotopes in the ammonite shell therefore correlates with ontogeny and is influenced by metabolic effects, probably linked to the shell growth rate. The isotope profiles further suggest vertical habitat changes during the ontogeny of the ammonites, indicating that the δ13Camm values might record a combination of environmental and metabolic signals. Taking into account studies on oxygen isotope fractionation of recent aragonitic and calcitic mollusc shells, a similar pelagic habitat is proposed here for both, ammonites and belemnites.

Characterisation and expression of the biomineralising gene Lustrin A during shell formation of the European abalone Haliotis tuberculata

The molluscan shell is a remarkable product of a highly coordinated biomineralisation process, and is composed of calcium carbonate most commonly in the form of calcite or aragonite. The exceptional mechanical properties of this biomaterial are imparted by the embedded organic matrix which is secreted by the underlying mantle tissue. While many shell-matrix proteins have already been identified within adult molluscan shell, their presence and role in the early developmental stages of larval shell formation are not well understood. In the European abalone Haliotis tuberculata, the shell first forms in the early trochophore larva and develops into a mineralised protoconch in the veliger. Following metamorphosis, the juvenile shell rapidly changes as it becomes flattened and develops a more complex crystallographic profile including an external granular layer and an internal nacreous layer. Amongst the matrix proteins involved in abalone shell formation, Lustrin A is thought to participate in the formation of the nacreous layer. Here we have identified a partial cDNA coding for the Lustrin A gene in H. tuberculata and have analysed its spatial and temporal expression during abalone development. RT-PCR experiments indicate that Lustrin A is first expressed in juvenile (post-metamorphosis) stages, suggesting that Lustrin A is a component of the juvenile shell, but not of the larval shell. We also detect Lustrin A mRNAs in non-nacre forming cells at the distal-most edge of the juvenile mantle as well as in the nacre-forming region of the mantle. Lustrin A was also expressed in 7-day-old post-larvae, prior to the formation of nacre. These results suggest that Lustrin A plays multiple roles in the shell-forming process and further highlight the dynamic ontogenic nature of molluscan shell formation.

Impacts of CO2-induced seawater acidification on coastal Mediterranean bivalves and interactions with other climatic stressors

The effects of seawater acidification caused by increasing concentrations of atmospheric carbon dioxide (CO2), combined with other climatic stressors, were studied on 3 coastal Mediterranean bivalve species: the mussel Mytilus galloprovincialis and the clams Chamelea gallina and Ruditapes decussatus. CO2 perturbation experiments produced contrasting responses on growth and calcification of juvenile shells, according to species and location. In the Northern Adriatic (Italy), long-term exposure to reduced pH severely damaged the shells of M. galloprovincialis and C. gallina and reduced growth for the latter species. Seawater in the Ria Formosa lagoon (Portugal) was consistently saturated in carbonates, which buffered the impacts on calcification and growth. After 80 days, no shell damage was observed in Portugal, but mussels in the acidified treatments were less calcified. Reduced clearance, ingestion and respiration rates and increased ammonia excretion were observed for R. decussatus under reduced pH. Clearance rates of juvenile mussels were significantly reduced by acidification in Italy, but not in Portugal. Both locations showed a consistent trend for increased ammonia excretion with decreasing pH, suggesting increased protein catabolism. Respiratory rates were generally not affected. Short-term factorial experiments done in Italy revealed that acidification caused alterations in immunological parameters of adult bivalves, particularly at temperature and salinity values far from the optimal for the species in the Mediterranean. Overall, our results showed large variations in the sensitivities of bivalves to climatic changes, among different species and between local populations of the same species. Expectations of impacts, mitigation and adaptation strategies have to consider such local variability.

Larval and post-larval stages of Pacific oyster (Crassostrea gigas) are resistant to elevated CO2.

The average pH of surface oceans has decreased by 0.1 unit since industrialization and is expected to decrease by another 0.3–0.7 units before the year 2300 due to the absorption of anthropogenic CO2. This human-caused pH change is posing serious threats and challenges to the Pacific oyster (Crassostrea gigas), especially to their larval stages. Our knowledge of the effect of reduced pH on C. gigas larvae presently relies presumptively on four short-term (<4 days) survival and growth studies. Using multiple physiological measurements and life stages, the effects of long-term (40 days) exposure to pH 8.1, 7.7 and 7.4 on larval shell growth, metamorphosis, respiration and filtration rates at the time of metamorphosis, along with the juvenile shell growth and structure of the C. gigas, were examined in this study. The mean survival and growth rates were not affected by pH. The metabolic, feeding and metamorphosis rates of pediveliger larvae were similar, between pH 8.1 and 7.7. The pediveligers at pH 7.4 showed reduced weight-specific metabolic and filtration rates, yet were able to sustain a more rapid post-settlement growth rate. However, no evidence suggested that low pH treatments resulted in alterations to the shell ultrastructures (SEM images) or elemental compositions (i.e., Mg/Ca and Sr/Ca ratios). Thus, larval and post-larval forms of the C. gigas in the Yellow Sea are probably resistant to elevated CO2 and decreased near-future pH scenarios. The pre-adapted ability to resist a wide range of decreased pH may provide C. gigas with the necessary tolerance to withstand rapid pH changes over the coming century.

Population dynamics and taphonomy of the Late Triassic (Carnian) freshwater bivalves from Krasiejów (Poland)

The Krasiejów clay pit (SW Poland) has so far been known for yielding mass accumulations of Late Triassic (Carnian) vertebrate fossils. However, unionoid bivalves occur abundantly within the 1 metre-thick shell-rich lacustrine interval at Krasiejów. They are most commonly preserved as shell imprints in the claystone or mudstone. A layer-by-layer quantitative sampling for shell external moulds was conducted directly in the bedding planes at two sites. The most numerous findings come from red and variegated layers in the upper part of this interval, which correspond to a well-aerated sediment. Single valves dominate at both sites and in all layers; valves in butterfly position are rare. The abundance of single valves throughout the sedimentation of the whole interval, both juveniles and adults, indicates that this interval represents the graveyard of a stable, reproducing population. The only exception is a bedding plane in the upper part of the lacustrine interval with numerous concretionary infills of closed valve interiors. They were presumably killed by a sudden load of sediment and, after the early diagenetic cementation was completed, they were winnowed from the mud. The mortality pattern is characterised by a high juvenile mortality (peak at about 13mm), and a slight increase in subadult mortality (peak at about 30mm; adult specimens reach 55mm). Complete lack of early juvenile shells representing the stage with prominent ornamentation may have resulted from predation rather than from size-selective post-mortem preservation. The course of ontogeny shows virtually isometric growth. The range of variability of shell proportions within and between layers suggests the succession of monospecific populations. The Krasiejów lacustrine interval represents the oldest insight into the dynamics and taphonomy of unionoid palaeocommunity.

Variation of Color and Ray Pattern in Juvenile Shells in Hatchery‐produced Freshwater Triangle Pearl Mussels, Hyriopsis cumingii, in China

AbstractThe variation and inheritance of juvenile shell color and pigmentation pattern in the freshwater mussel, Hyriopsis cumingii, were reported in 1‐yr‐old progeny of eight families. There were three distinctive phenotypes of shell color and pigmentation patterns observed, including a greenish‐brown shell with radial rays, yellowish‐brown shell with radial rays, and yellowish‐brown shell without radial rays. There were no greenish‐brown individuals without radial rays. The shell color phenotypes showed variation with the growth in juvenile Stage I (1–3 cm in shell length), and the percentage of individuals with radial rays increased once they reached a shell length of 11 mm and then stabilized after reaching 20 mm in shell length. Shell color differentiation became more apparent at a shell length of 26 mm. Results of chi‐square tests of the segregation ratio of shell color or ray phenotypes obtained from eight families at juvenile Stage II (6–9 cm in shell length) suggested that greenish‐brown is controlled by a dominant allele (G) and yellowish‐brown‐shell phenotype is by a recessive allele (y); the ray pattern phenotype is controlled by a recessive (r) and a dominant allele (R) at a single locus. Shell color phenotypes may be a useful genetic marker for future selective breeding of triangle pearl mussels.

Are diminutive turtles miniaturized? The ontogeny of plastron shape in emydine turtles

Miniaturization, or the evolution of a dramatically reduced body size compared to related lineages, is an extraordinarily widespread phenomenon among metazoans. Evolutionary biologists have been fascinated by miniaturization because this transition has occurred numerous times, often among close relatives, providing a model system for studying convergent evolution and its underlying mechanisms. Much of the developmental work describing the ontogeny of miniature species suggests that paedomorphosis is the predominant avenue of miniaturization. Nevertheless, specific alterations to ontogeny appear highly variable, so that even related lineages with similar miniaturized traits produce those similarities via distinct ontogenetic paths. One major vertebrate group that has been overlooked in research on miniaturization is turtles. In the present study, we examined patterns of shape change in the plastron (the ventral part of the shell) over the course of ontogeny in a small clade of turtles (Emydinae) aiming to investigate whether two independently evolved diminutive members of the clade (Glyptemys muhlenbergii and Clemmys guttata) should be considered as miniaturized. We employ geometric morphometric methods to quantify the patterns of shape change these potentially miniaturized species and their relatives undergo during ontogeny, and use molecular phylogenetic trees to reconstruct ancestral conditions and provide information on the polarity of shape changes. We find that differing changes in ontogenetic parameters relative to ancestral conditions accompany the evolution of small size in emydines: G. muhlenbergii changes the duration of ontogeny and rate of shape change, whereas C. guttata changes growth rate. The observed ontogenetic repatterning of these species is reminiscent of changes in ontogeny and life history often found in miniaturized taxa. However, we conclude that C. guttata and G. muhlenbergii are not truly miniaturized because they still produce typical adult shell morphologies, and larger emydines display comparable ontogenetic flexibility. Because no emydines carry juvenile shell features forward into adulthood, we speculate that few, if any turtles, will show paedomorphic shell traits without corresponding changes in defensive strategy because such shells may offer insufficient protection.

Faunal dynamics of gastropods in the Bathonian (Middle Jurassic) ore-bearing clays at Gnaszyn, Kraków-Silesia Homocline, Poland

ABSTRACT Kaim, A. 2012. Faunal dynamics of gastropods in the Bathonian (Middle Jurassic) ore-bearing clays at Gnaszyn, Kraków-Silesia Homocline, Poland. Acta Geologica Polonica, 62(3), 367-380. Warszawa. The succession of gastropods in the Gnaszyn section is quite monotonous and shows significant changes only in the proximity of concretion layers, at least partially because of diagenetic reasons. Otherwise, the section is dominated by gastropods (cylidrobullinids, bullinids, and mathildids) most of which preyed probably on sedentary organisms (polychaetes and/or coelenterates) that possibly flourished on the sea bottom at that time. The other groups of gastropods are represented by larval or juvenile shells. Their presence shows that the environmental conditions that were probably unfavourable for gastropods living directly on the sea bottom most likely because of a soupy substrate consistency, possible oxygen deficiency near the sediment-water interface and/or oxygen content fluctuations. Adult and/or subadult individuals of these gastropods occur only in the higher part of the section, reflecting a time when these conditions improved. A new heterostrophic gastropod species, Promathildia gedli, is described.

SEM observations on larval shell morphology of Manila clam Ruditapes philippinarum and their utility

Manila clam Ruditapes philippinarum is common and abundant on Japanese tidal flats, forming a commercially important clam fishery. However, annual catches of Manila clam have decreased drastically since 1975–1985. To study larval recruitment processes of Manila clam, we carried out scanning electron microscopy (SEM) observations on larval and juvenile shells of clams reared at 20 and 24 °C. There was no significant difference in final shell length of trochophores between 20 and 24 °C. However, the larval duration was much longer and the shell length of settled size of pediveligers was much larger for clams reared at 20 °C than those reared at 24 °C. These findings suggest that larval duration and growth, as well as settlement size, may vary markedly depending on temperature (and probably on season). The larval shell morphology of Manila clam can provide essential information about larval recruitment processes.

Microchemistry of juvenile Mercenaria mercenaria shell: implications for modeling larval dispersal

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 465:155-168 (2012) - DOI: https://doi.org/10.3354/meps09895 Microchemistry of juvenile Mercenaria mercenaria shell: implications for modeling larval dispersal A. M. Cathey1,*, N. R. Miller2, D. G. Kimmel3 1Department of Biology, East Carolina University, Greenville, North Carolina 27858, USA 2Department of Geological Sciences, The University of Texas at Austin, Austin, Texas 78712, USA 3Department of Biology, Institute for Coastal Science and Policy, East Carolina University, Greenville, North Carolina 27858, USA *Email: catheya06@students.ecu.edu ABSTRACT: The elemental signature of trace and minor elements within biominerals has been used to investigate the larval dispersal of bivalves. We investigated the potential of this technique by examining elemental signals in juvenile shells of the hard clam Mercenaria mercenaria within an estuarine−lagoonal system near Cape Lookout, North Carolina, USA. We assessed the spatial distinction (~12 to 40 km) and temporal stability (fall versus spring) of elemental concentrations using inductively coupled plasma mass spectrometry (ICP-MS). Twelve minor and trace elements were present at detectable levels in all shell samples: calcium (Ca), manganese (Mn), aluminum (Al), titanium (Ti), cobalt (Co), copper (Cu), barium (Ba), magnesium (Mg), zinc (Zn), lead (Pb), nickel (Ni), and strontium (Sr). Discriminant function analyses (DFA) using metal to Ca ratios as independent variables correctly assigned hard clams to their site of collection with 100% success from both fall and spring sampling events. Mn:Ca ratio proved to be the most effective discriminator explaining 91.2 and 71.9% of our among-group variance, respectively. Elemental concentrations within juvenile shell differed temporally. A combined DFA approach using shell from both sampling events obtains a classification success of 81.9%. Mn:Ca ratio explained the bulk of among group variance (89.9%) and was consistently different among water masses during each season. Our results demonstrate for the first time the existence of small-scale spatial differences (~12 km) in the elemental chemistry of juvenile bivalve shell exclusively within an estuarine−lagoonal system. Our results suggest that the validation of a similar chemical signal of M. mercenaria larval shells is possible and may be used to trace the dispersal trajectory of this economically important species. KEY WORDS: Mercenaria mercenaria · Microchemistry · Larval dispersal · Population connectivity · Estuary · Plasma mass spectrometry Full text in pdf format PreviousNextCite this article as: Cathey AM, Miller NR, Kimmel DG (2012) Microchemistry of juvenile Mercenaria mercenaria shell: implications for modeling larval dispersal. Mar Ecol Prog Ser 465:155-168. https://doi.org/10.3354/meps09895 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 465. Online publication date: September 28, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

A new species of Urocopitid land snail from Haiti and a discussion of the genus Autocoptis (Gastropoda: Urocoptidae)

Autocoptis paulsoni n. sp. is described from Haiti. It is characterized by its large size, its cylindrical-tapered shape, its fine costate sculpture on the teleoconch, a distinct but weak circum basal keel and its abbreviate conical juvenile shell. It is most similar to Autocoptis gruneri (Dunker 1844), which is redescribed, and its distribution is reviewed. The taxonomic status of the genus Autocoptis Pilsbry 1902 and its subgenus Urocoptola Clench, 1 935 are reviewed. The genus is endemic to Hispaniola and satellite islands.

The functional morphology and inferred biology of the enigmatic South African ‘quadrivalve’ bivalve Clistoconcha insignis Smith, 1910 (Thracioidea: Clistoconchidae fam. nov.): another anomalodesmatan evolutionary eccentric

ABSTRACT The commarginally-ribbed shell of Clistoconcha insignis is anteriorly globose, posteriorly short, tapered and characterised by dorsal cracks, which arise from just posterior to the juvenile shell and extend to the ventral margin of each valve. In effect, thereby, a unique quadrivalve structure is formed. Shell morphology suggests that following a short planktonic larval phase, an approximately isomyarian, crawling, juvenile is formed. Upon choice and adoption of a place suitable for adult occupation, which is believed to be crevices and pits on the undersides of large stones, situated within shallow subtidal sands, the adult shell is formed. With growth, the shell becomes distorted and, finally, assumes a form in which the valves are marginally united, closing the pedal gape, except posteriorly (to allow for extension of the siphons) and mid-dorso-ventrally surrounded by a calcareous callus that is formed from secretions produced by glands of the outer epithelium of the mantle. Dissection, sectioning and examination of a single preserved specimen have confirmed that Clistoconcha insignis is a member of the Anomalodesmata and is assigned to a new family, Clistoconchidae, with affinities to the Thraciidae (Thracioidea). It is, however, structurally and functionally, and thus convergently, most similar to the endobenthic representatives of the Laternulidae and Periplomatidae, which also possess, albeit only partial, dorso-ventral shell cracks. The secretion of a callus, probably to sustain the shell's integrity following fracturing as a result of adduction stresses and damage, is reminiscent of the similarly anomalodesmatan representatives of the Clavagelloidea but is produced in a uniquely different and analagous manner. The sunken and posteriorly oriented ligament of C. insignis concludes a trend in the Thracioidea towards posterior shell and ligament foreshortening to create a unique form that dramatically broadens our understanding of not only anomalodesmatan, but also bivalve, adaptive radiation.

Early ontogeny of Middle Jurassic hiatellids from a wood-fall association: implications for phylogeny and palaeoecology of Hiatellidae

We provide a detailed description of exceptionally well-preserved specimens of Hiatella (Pseudosaxicava) phaseolus (Eudes-Deslongchamps) from Middle Bathonian (Middle Jurassic) clays of the CzA™stochowa Ore-bearing Clay Formation at Gnaszyn (southern Poland). The juvenile shell is illustrated for the first time, allowing detailed interpretation of the ontogenetic history of these bivalves. The specimens settled on sunken driftwood that served as an attachment surface and thus acted as a ‘benthic island’ on the otherwise muddy seafloor. A review of the Mesozoic record of the bivalve family Hiatellidae shows that the group appeared in the earliest Jurassic, shortly after the end-Triassic extinction event. The Jurassic species of Hiatella (Pseudosaxicava) do not significantly differ from the Recent species of Hiatella (Hiatella) with regard to major shell characters. However, the absence of hinge teeth and the presence of multiple rows of tiny tubercles on the juvenile dissoconch of Pseudosaxicava clearly distinguish the two subgenera. Although highly variable with regard to morphology and behaviour (boring, nestling or byssal attachment), the Hiatellidae are a conservative group that have not changed significantly since the Mesozoic.

Umbonal musculature and relationships of the Late Triassic filibranch unionoid bivalves

Exceptionally well-preserved Late Triassic unionoids from Silesia, Poland, show prominently ornamented juvenile shells and umbonal muscle attachments that are similar to Margaritifera, which are anatomically the least derived among extant unionoids. Their phosphatized (originally chitinous and impregnated with calcium phosphate) gill supports lacked transverse connections, and occasionally some of them were separated from others, being thus at the filibranch grade, like their trigonioid ancestors. Several separate small foot elevator attachments in these unionoids indicate Trigonodidae adaptation to marine or brackish water, in which the original trigonioid strong single attachment was already split into two in the Early Triassic. The ribbing of juvenile shells suggests a change to deeper infaunal life for juvenile stages, and generally less efficient near-surface locomotion, with a wedge-like foot, in adults. Much later the unionoids became eulamellibranchial, which promoted the brooding of the fish that their larvae parasitize. To accomodate the classification of the order under this scenario of evolutionary changes, a new suborder Silesunionina is proposed for its filibranch members. It includes the Silesunionidae fam. nov., with the location of umbonal muscles similar to that in the extant underived unionoids, and the Unionellidae fam. nov., with umbonal muscles attached to the external wall of the umbonal cavity. The early Late Triassic (Carnian) Silesunio parvus gen. et sp. nov. and latest Triassic (Rhaetian) Tihkia(?) silesiaca sp. nov. are proposed. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 163, 863–883.

Possible functions of Dpp in gastropod shell formation and shell coiling

We examined dpp expression patterns in the pulmonate snail Lymnaea stagnalis and analyzed the functions of dpp using the Dpp signal inhibitor dorsomorphin in order to understand developmental mechanisms and evolution of shell formation in gastropods. The dpp gene is expressed in the right half of the circular area around the shell gland at the trochophore stage and at the right-hand side of the mantle at the veliger stage in the dextral snails. Two types of shell malformations were observed when the Dpp signals were inhibited by dorsomorphin. When the embryos were treated with dorsomorphin at the 2-cell and blastula stages before the shell gland is formed, the juvenile shells grew imperfectly and were not mineralized. On the other hand, when treated at the trochophore and veliger stage after the shell gland formation, juvenile shells grew to show a cone-like form rather than a normal coiled form. These results indicated that dpp plays important roles in the formation and coiling of the shell in this gastropod species.