Aspidogaster conchicola is a form not uncommon in Anodon, Unio and certain fresh-water Gastropods.
The concrescence, then, of the free edge of the reflected lamellae of the gill-plates of Anodon is very extensive.
The organization of the oyster, as compared with that of a typical lamellibranch such as Anodon, is brought about by the reduction of the anterior part of the body accompanying the loss of the anterior adductor, and the enlargement of the posterior region.
The heart and pericardial chamber in the oyster lie along the anterior face of the adductor muscle, almost perpendicular to the direction of the gills, with which in Anodon they are parallel.
In Anodon and the majority of lamellibranchs the ventricle surrounds the intestine; in the oyster the two are quite independent, the intestine passing above the pericardium.