Family Ostreidae - oysters

  Order
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  Class
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Bivalvia
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  No. of Species in Ref.
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  Environment
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Fresh : No | Brackish : Yes | Marine : Yes
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  Remark
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Under order Filibranchiata in Ref. 2797. To about 20 cm. Marine and estuarine (Ref. 94508). Shell solid, often irregularly shaped, inequivalve, cemented to the substrate by the left (lower) valve which is generally larger and deeper. Right (upper) valve quite flat, often with thin, concentrically arranged, imbricating plates of horny material tending to make a protruding fringe beyond the shell margin. Outer suface commonly, at least on left valve, with radial folds or ribs which may affect the shell margin. Ligamental area with a shallow median groove and two lateral thickenings. Hinge without teeth. A more or less deep umbnal cavity, sometimes present. Interior of shell porcelaneous, sometimes with irregular chalky deposits or with a subnacreous tinge. A single (posterior) adductor muscle scar, generally median in position or nearer to the venral margin than to the hinge. Pallial line without a sinus, obscure to absent. Internal margins smooth or with simple short chomata, which may be restricted to the hinge surroundings. Gills of eulamellibranchiate type, with folded branchial sheets. Foot and byssus atrophied. Pallial lobes free, with marginal tentacles (Ref. 348).
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Ref.
[ e.g. 3742]                  
Glossary
                      [ e.g. cnidaria]
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