Functional Morphology, Micro-anatomy, and histology of the 'Sydney Cockle' Anadara trapezia (Deshayes )(Lamellibranchia: arcidae).

Abstract

The anatomy and histology of the Australian lamellibranch, Anadara trapezia (Deshayes, 1839), are described. The pattern of the ciliary currents on the ctenidia, mantle, foot, and labial palps is similar to those in the related species Arca tetragona and Glycymeris glycymeris. However, A. trapezia differs from these forms in having a more extensive development of the ridges on the labial palps, as well as in the ciliation of the ctenidial filaments. The possible correlation between the arrangement of cilia on the ctenidial filaments and the extent of the ridged areas of the palps is discussed. The structure of the stomach is closely similar to that of Glycymeris. The digestive diverticula, with their ciliated ducts, are typical of the Anisomyaria and Eulamellibranchia. The gastric shield appears to be secreted by the epithelial cells of the stomach. Secretion is intermittent, resulting in stratification of the shield, and is indicated by strongly periodic acid-Schiff(P.A.S.)-positive material which forms in the neighbourhood of the epithelial cell nuclei and then migrates to the apical ends of the cells to be added to the shield. Many gland cells, both intra-epithelial and subepithelial, are present in the foot, mantle, and palps. There are several types, differing in their staining reactions and in the appearance of their cytoplasm in fixed and sectioned material. It is suggested that those glands whose cytoplasm gives a very strong positive reaction with P.A.S. may produce a lubricating secretion, while those which give reactions for mucin but are not so strongly P.A.S.-positive may form a tacky mucus suitable for holding particulate matter to facilitate transport by ciliary currents. In the connective tissue there are stellate cells embedded in the gelatinous ground substance. Another type of cell, laden with coarse brownish granules is present in some regions, especially around the kidney tubules. "Leydig's cells", which have been observed in the connective tissue of a number of molluscs, and which store glycogen in these forms, do not appear to be present in A. trapezia. Glycogen is present, but is scattered through the ground substance in the form of granules. It is suggested that the glycogen may be deposited in the fine processes of the stellate cells.