Cleansing Mechanisms and the Function of the Fourth Pallial Aperture in<i>Spisula Subtruncata</i>(Da Costa) and<i>Lutraria Lutraria</i>(L.)

Abstract

Spisula subtruncata is a shallow-burrowing member of the Mactridae which inhabits silty sand. Adaptations to such conditions include long frontal cilia on the gills (Atkins), and the presence of a siphonal membrane with associated mantle folds over-arching a waste canal, as postulated by Kellogg for allied species. The mantle edges are free ventrally, but are normally closely applied except for a short distance at the base of the inhalant siphon, an effective fourth pallial aperture being so formed. Through this opening material from the waste canal is ejected. Lutraria lutraria is a deep-burrowing species belonging to the same family. The general resemblance to Mya arenaria is due to convergence. Cleansing currents resemble those of Spisula subtruncata and there is a similar waste canal, but the siphonal membrane and the long frontal cilia associated with a silty environment are absent.