On the Ciliary Mechanisms and Interrelationships of Lamellibranchs: PART I: New Observations on Sorting Mechanisms

Abstract

ABSTRACT The gills of Solen marginatus, Ensis siliqua, and Ensis arcuatus are synaptorhabdic or eulamellibranchiate, and the lamellae plicate and heterorhabdic. The latero-frontal cilia are large; there are in addition small subsidiary laterofrontal cilia. The frontal cilia on the filaments forming the bottom of the plical grooves are fine and beat dorsally. In the two species of Ensis the frontal cilia on the filaments forming the sides and apices of the plicae are arranged in two tracts with the effective beat in opposite directions; in Solen marginatus in three tracts, a median one of coarse cilia beating ventrally and two outer ones of fine cilia continuously beating dorsally. In both genera the movement of particles in the plical grooves is dorsalward; on the crests mainly ventralward; on the sides of the plicae ventral or dorsal according apparently to their type and number. Along the marginal grooves of the demibranchs, between the bases of the two demibranchs of a gill, and along the dorsal edges of all the ascending lamellae, currents are towards the mouth. The gills of Cultellus pellucidus are synaptorhabdic or eulamelhbranchiate, and the lamellae flat and homorhabdic. The ventral edge of the outer demibranch is ungrooved. On the frontal surfaces of the filaments of both lamellae of the inner and the ascending lamella of the outer demibranch there are, in addition to fine cilia, a tract of long, coarse ones which beat ventrally. The fine frontal cilia, which alone are present on the descending lamella of the outer demibranch, beat dorsally, and, so far as could be ascertained, the tracts of fine cilia on the other three lamellae of the gill also beat dorsally. The obvious frontal currents are toward the ventral edge on both lamellae of the inner and on the ascending lamella of the outer demibranch, and dorsalward on the descending lamella of the outer demibranch. Along the marginal groove of the inner demibranch, between the bases of the two demibranchs of a gill, and along the dorsal edges of all the ascending lamellae, currents are towards the mouth.