Gross Structure of the Adductor Muscles of Some Pelecypods

A study of the gross structure of adductor muscles of the following pelecypods showed that they conform to Morton’s grouping into the a) "Protobranchia" (Nucula proxima and Yoldia limatula), b) "shallow-burrowing lamellibranchs" (Clinocardium ciliatum, Venericardia borealis, Astarte undata, Arctica islandica, Venus mercenaria, and Spisula solidissima), c) "surface attached lamellibranchs" (Mytilus edulis, Modiolus modiolus, Modiolus demissus, Placopecten magellanicus, and Crassostrea virginica), d) "deep-burrowing and immobile lamellibranchs" (Ensis directus, Hiatella arctica, and Mya arenaria); thus providing more evidence for his classification. The adductor muscle is divided into two portions — translucent and opaque — except in the "deep-burrowing and immobile lamellibranchs", which have opaque muscles only.