Protein scaffold bivalve mollusca3/27/2023 ![]() ![]() This enabled us to identify the critical elements of a " basic tool kit " for calcification processes, which were conserved across the taxa irrespective of the shell morphology and arrangement of the crystal surfaces. In this study, the shell matrix proteins (SMPs) of four highly divergent bivalves (The Pacific oyster, Crassostrea gigas the blue mussel, Mytilus edulis the clam, Mya truncata, and the king scallop, Pecten maximus) were analyzed in an identical fashion using proteomics pipeline. Although, there is a general consensus that a minimum basic protein tool kit is required for shell construction, to date, this remains undefined. A suite of proteins exported to the shell matrix space plays a significant role in controlling these features, in addition to underpinning some of the physical properties of the shell itself. These structures circulate currents of water needed for feeding and breathing.Bivalves have evolved a range of complex shell forming mechanisms that are reflected by their incredible diversity in shell mineralogy and microstructures. The mantle (the sheet-like organ that produces the shell) is large and often fused at the edges to form inhalent and exhalent siphons. However, these are large and fold back on themselves providing a highly efficient surface for filter feeding. Bivalves have just a single pair of gills (‘*ctenidia*’). The muscular foot typically has no sole, is flattened laterally and is used for burrowing and general locomotion. Inside the shell, the animal has a simple head without eyes or radula (the rasping, ribbon-like tongue used for feeding in other mollusc groups). ![]() The freshwater mussel Mytilopsis leucophaeata showing the incurrent and excurrent siphons. Rising above the hinge line on each valve is a swelling called the umbo, the oldest part of the shell. ![]() Lucina exasperata has a heterodont hinge, with fewer but larger and differently sized hinge teeth. Arca senilis has a taxodont hinge, with many small, similarly sized interlocking teeth. Top: Arca senilis Bottom: Lucina exasperataīivalve molluscs are completely enclosed by a shell Shown here are two species of bivalves with very different hinge structures. Two species with very different hinge structure. ![]() Venus clam Callista erycina showing the hinge ligament that joins the two halves of the shell. Differences in the nature of the hinge teeth are important in the classification of bivalves. The hinge teeth (consisting of cardinal and lateral teeth) interlock on the two valves preventing slippage. The hinge ligament is usually external to the shell, but in many species has shifted to an internal position between the hinge teeth. The adductor muscles contain both smooth and striated fibres, enabling sustained (‘catch muscle’) and rapid shell closure. This means that when the adductor muscles relax, the ligament acts like a spring and the shell opens. When the shell is closed, the top part of the hinge ligament is stretched and the lower part is compressed. A hinge ligament made of elastic protein joins the two halves of the shell together, and large adductor muscles between the two valves hold them closed. Bivalve molluscs are completely enclosed by a shell made of two valves hinged at the top. ![]()
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