Quarterly Journal of Microscopical Science, Vol s3-97, 541-567, Copyright © 1956 by Company of Biologists

Observations on the Stomach and Digestive Diverticula of the Lamellibranchia

II. The Nuculidae

¹ Department of Zoology, University of Glasgow

The anatomy and histology of the stomach and digestive diverticula and the physiology of digestion in the Nuculidae have been investigated.

The stomach is relatively large and possesses a well-developed style sac, although a rod-like crystalline style is absent. Sorting areas are present in the dorsal region of the stomach but the ciliary currents are relatively weak and have little effect on the ingested material.

The digestive diverticula consist of three regions, the physiological relations of which have not been fully elucidated. The three regions are: (a) a much-branched system of non-ciliated main ducts, the epithelium of which shows a well-developed brush-border; (b) short, unbranched ciliated secondary ducts; (c) irregularly branched blindly ending tubules. The epithelium of the tubules is divided into two regions, one composed of large cells containing numerous conspicuous granules and the other of less frequent and smaller darkly staining cells. Each darkly staining cell bears asingle flagellum.

Separate mucous glands cannot be demonstrated in any part of the stomach or digestive diverticula.

The epithelium of the style sac secretes an amylase and a lipase. Extracts of the digestive diverticula contain an amylase, a lipase, and a protease.

Unlike the majority of lamellibranchs, fluid and solid particles do not appear to enter the digestive diverticula from the stomach and in no part of the gut or of the diverticula is there ever any evidence of intracellular digestion. It is suggested that in the Nuculidae digestion is exclusively extra-cellular and confined to the stomach. The soluble products are absorbed by the epithelium of the stomach and first part of the intestine.

The diverticula of the rest of the Lamellibranchia are compared with those of the Nuculidae. While the Nuculidae are in many respects primitive lamellibranchs, the conclusion is reached that the digestive diverticula present many specialized features possibly correlated with the method of feeding.