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The functional morphology of Sinonovacula constricta with a discussion on the taxonomic status of the Novaculininae (Bivalvia).

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Abstract

Sinonovacula constricta is representative of two genera of deep burrowing bivalves hitherto placed in the Novaculininae of the Tellinacea. This species, widely cultured in China, has not previously been critically examined. Aspects of its anatomy show that it should more properly be placed in the Solenacea. The presently accepted classification of this superfamily suggests that it should be placed close to Pharella in the Cultellidae but it is clear that the group requires more detailed re-examination.

Sinonovacula is somewhat posteriorly elongate with long separate siphons. The anterior pedal gape acts as a valve to the piston-like foot enabling rapid reburrowing to occur. Sensory tentacles around the pedal gape respond to mechanical disturbance and water can be squirted from the gape to, presumably, flush away the source of irritation. Modifications of this kind are rare in the Bivalvia.

The anatomy of Sinonovacula is described and related to its life style as a suspension feeder in soft intertidal muds. The ciliary currents of the mantle cavity are powerful, the labial palps in particular being large as compared with the relatively small ctenidia. The stomach is adapted for dealing with large amounts of food, though the sorting areas are not extensive; principal sorting is clearly the function of the labial palps. The style sac and mid-gut are separate (unlike the conjoined style sac and mid gut of the Tellinacea), and ensure separation of the style from the sediment loaded mid gut.

In many ways Sinonovacula foreshadows the highly modified true razor shells and conditions in these bivalves can be accounted for by further posterior elongation of a bivalve essentially similar to Sinonovacula.

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Ancillary