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The geographic boundaries of many important habitat-building shallow estuarine oyster (Family Ostreidae) species are poorly understood, especially in subtropical and tropical waters. These keystone species often have extensive historical and extant ranges, in part because of their ability to adapt to diverse environmental conditions and the transfer and introduction of a few species worldwide for aquaculture production. In addition, oysters exhibit morphological plasticity additionally confounding species identification and taxonomy. Molecular techniques have led to significant improvements in oyster systematics and taxonomy but have not been applied to oysters from many tropical regions, including the coastal areas of the Indian Ocean such as Bangladesh. Because species' identification based on morphological traits alone, in this case primarily shell characteristics, were inadequate, phylogenetic analyses of mitochondrial cytochrome oxidase subunit I gene fragments was also done to confirm the identity of oyster specimens collected from Bangladesh coastal waters. Phylogenetic analyses of collected oyster samples confirmed the two monophyletic subclades of the Ostreidae family Crassostrea and Saccostrea, and five oyster lineages from the region of Bangladesh were identified: Crassostrea gryphoides, Crassostrea belcheri, Saccostrea cuccullata lineage B, S. cuccullata lineage F, and Saccostrea mordax. A new addition to the list of Crassostrea species, C. belcheri was found in Bangladesh, but C. belcheri, C. gryphoides, and S. cuccullata are considered “common” species in the neighboring states of India and Myanmar indicating a widespread distribution of these species along the entire coast of the Bay of Bengal. However, S. mordax, is a new record for the Bay of Bengal region including the coastal waters of Andaman and Nicobar Islands, and thus extends the geographical distribution of this species.

The morphological plasticity of bivalve species may impair their correct identification. Pisidium species (Sphaeriidae) are difficult to distinguish, notably the common pea clam, Pisidium casertanum (Poli, 1791), which is a polymorphic species, often misidentified and confused with other Pisidium species. This is especially true since this species is the most euryecious of the genus, being able to colonize very different habitats. In this study, elliptic Fourier Analysis, a geometric morphometric method, was used to assess intraspecific variation in P. casertanum. Sampling of specimens was done in three habitat types-springs, lakes and streams-in the Mediterranean biodiversity hotspot region, using the Sebou basin in Morocco as a study area. In addition to the geometric morphometric method, linear measurements of the shell were used to assess growth patterns. Results revealed differences in the hinge plate, which is broader in shells collected from lakes, whereas it is higher in shells of springs. The geometric morphometric method clearly showed shape differences between individuals of the three habitats. Specimens of lakes were the most distinguishable, presenting more elongated shells than those from springs and streams, which are shorter but higher. Individuals from the three habitat types presented a negative allometric growth pattern whereby the shell of animals grows more slowly in height than in length. The use of linear and geometric morphometric methods led to conclude that the morphology of P. casertanum is, in fact, highly influenced by its environment, in particular, its habitat type., The authors would like to thank the High Commission for Water and Forests, Rabat (HCEFLCD) for granting permission to collect in the Moroccan basins. The authors are also grateful to the late Ulrich Bößneck for helping in the field and for fruitful discussions on Moroc can Sphaeriidae.

Effects of contamination on aquatic organisms have been investigated and employed as biomarkers in environmental quality assessment for years. A commonly referenced aquatic organism, mollusks represent a group of major interest in toxicological studies. Both gastropods and bivalves have external mineral shells that protects their soft tissue from predation and desiccation. These structures are composed of an organic matrix and an inorganic matrix, both of which are affected by environmental changes, including exposure to hazardous chemicals. This literature review evaluates studies that propose mollusk shell alterations as biomarkers of aquatic system quality. The studies included herein show that changes to natural variables such as salinity, temperature, food availability, hydrodynamics, desiccation, predatory pressure, and substrate type may influence the form, structure, and composition of mollusk shells. However, in the spatial and temporal studies performed in coastal waters around the world, shells of organisms sampled from multi-impacted areas were found to differ in the form and composition of both organic and inorganic matrices relative to shells from less contaminated areas. Though these findings are useful, the toxicological studies were often performed in the field and were not able to attribute shell alterations to a specific molecule. It is known that the organic matrix of shells regulates the biomineralization process; proteomic analyses of shells may therefore elucidate how different contaminants affect shell biomineralization. Further research using approaches that allow a clearer distinction between shell alterations caused by natural variations and those caused by anthropogenic influence, as well as studies to identify which molecule is responsible for such alterations or to determine the ecological implications of shell alterations, are needed before any responses can be applied universally. Fil: Yokota Harayashiki, Cyntia Ayumi. Universidade Federal de Sao Paulo.; Brasil Fil: Marquez, Federico. Universidad Nacional de la Patagonia "San Juan Bosco"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto de Biología de Organismos Marinos; Argentina Fil: Cariou, Elsa. Universite de Nantes; Francia Fil: Castro, Ítalo Braga. Universidade Federal de Sao Paulo.; Brasil

The use of elastoplastic models in calculations of shell and plate structures, or more generally in stress situations in which one normal stress component is forced to be zero, usually leads to complicated algorithms. This leads to cumbersome programming, which in turn may easily entail errors in the code. Moreover, the fraction model for cyclic plasticity cannot be used within most algorithms since the normal stress perpendicular to the plane of the element is not necessarily zero for each of the fractions. In this contribution an algorithm will be presented that enforces a zero-stress condition at integration point level, while obviating the need to develop special subroutines for plane-stress or shell plasticity. The algorithm is based upon an implicit integration of the stress-strain law and can be combined with the newly developed technique of consistent tangent operators.

In this study, I identified adult, post-larval and veliger larvae of Dreissena polymorpha and Dreissena bugensis, using analysis of shell morphology, and restriction analysis of the cytochrome c oxidase subunit I (COI) mitochondrial gene. Principal component analysis of shell morphology showed that deep (Dreissena bugensis "profunda") and shallow (Dreissena bugensis s.s) quagga mussels exhibit shell plasticity with depth, while Dreissena polymorpha do not. Morphological analysis, restriction analysis and sequencing of the mitochondrial gene COI suggest that Dreissena bugensis "profunda" is a phenotype of Dreissena bugensis s.s. Transplanted and in-situ Dreissena polymorpha, Dreissena bugensis s.s and Dreissena bugensis "profunda" were collected from the wave zone, epilimnion and hypolimnion and analyzed for lipid concentration and gametogenic development. Results showed that Dreissena polymorpha had a preferred temperature typical of the Lake Erie wave zone, which ranged from 18$\sp\circ$C-24$\sp\circ$C, while both Dreissena bugensis s.s and Dreissena bugensis "profunda" had preferred temperatures typical of the Lake Erie hypolimnion, which ranged from 7$\sp\circ$C-9$\sp\circ$C. However, Dreissena bugensis s.s had a higher preferred temperature than did Dreissena bugensis "profunda". Substrate type was not significantly correlated with mussel lipid concentration. All taxa showed approximately synchronous spawning in the wave zone and epilimnion, indicating that all taxa are equally capable of reproduction in these zones. However, Dreissena polymorpha showed no gametogenesis or spawning in the hypolimnion. Both lipid and gametogenic analysis suggest that while all dreissenids can successfully colonize the wave zone and epilimnion of the Great Lakes, Only Dreissena bugensis s.s and Dreissena bugensis "profunda" can successfully colonize the hypolimnion.