Family Pinnidae - pen shells

  Order
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  Class
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Bivalvia
  No. of Genera in Ref.
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  No. of Species in Ref.
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  Environment
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Fresh : No | Brackish : No | Marine : Yes
  Aquarium
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  First Fossil Record
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  Remark
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Under order Filibranchiata in Ref. 2797. Shell large and brittle, equivalve, laterally compressed, subtrigonal in outline, ventrally and posteriorly gaping; very inequilateral, pointed in front, wide and flexible behind. Umbones at anterior end which is eroded and internally closed by a series of small transverse partitions. Outer sculpture mainly composed of radial ribbing, smoothish or provided with imbricated scales or spines, and often crossed by concentric undulations ventrally. Periostracum usually absent. Ligament linear, recessed in a narrow groove along dorsal margin. Hinge without teeth. Interior of shell with a thin nacreous layer which is restricted to the anterior half of valves. Two unequal adductor muscle scars, the anterior relatively small and placed in the anterior angle of shell, the posterior large and situated about midlength. No pallial sinus. Internal margins thin, smoothish, reflecting the external sculpture. Gills of eulamellibranchiate type, with folded branchial sheets. Foot conical, elongate and grooved, with a profuse silky byssus. Siphons absent. Mantle widely open, papillate on margins. Sessile animals, living generally partly embedded in heterogenous soft bottoms, with the narrow anterior tip of shell downwards, and attached to various hard elements of the substrate by means of long byssal threads. The posterior gape of the flexible shell can be closed by contraction of the adductor muscles. In relation to their vertically embedded mode of life, the Pinnidae have developed several unique anatomical features: a pair of special gutter-shaped canals inside the mantle lobes, to remove rapidly sediment material from the anterior portion of the mantle cavity, and a protrusible pallial organ above the posterior adductor muscle, to clear away debris from the posterior part of the shell. Sexes separate. Free-swimming larval stage present. Pinnidae have a noticeable economic importance in the western Pacific. They are actively collected for food in Japan and surrounding areas, as well as in Polynesia and several other Indo-Pacific island groups. In Polynesia, shells are carved to form decorative ornaments, and entire valves of large specimens are sometimes used as plates by native populations (Ref. 348).
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  Division
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  Main Ref.
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Ref.
[ e.g. 9948]                       
Glossary
                    [ e.g. cephalopods]


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