THE GROSS AND MICROSCOPIC ANATOMY OF THE DIGESTIVE TRACT OF THE OYSTER CRASSOSTREA VIRGINICA (GMELIN)

Abstract

The gross and microscopic anatomy of the digestive tract of Crassostrea virginica (Gmelin), the common oyster of commerce of the North Atlantic Coast, is described. The dorsoventrally compressed mouth bounded by two pairs of labial palps leads into a crescentic oesophagus, thence to the anterior chamber of the stomach from which a complex caecum extends into anteriorly and posteriorly directed spiral appendices. The posterior chamber of the stomach bears a chondroid gastric shield and leads into an elongated chamber which is incompletely divided by two typhlosoles into a style-sac and mid-gut. The intestine is divisible into ascending, median, and descending limbs, the latter merging into the rectum which terminates on the dorsal surface of the adductor muscle. Extensively branched tubular digestive diverticula exit from the stomach by a series of ducts along the margin of the caecum and the posterior stomach. The complete digestive tract is lined by a simple columnar epithelium which is ciliated throughout with the exception of the upper lip or fused external palps, the lower side of the gastric shield in the posterior stomach, and the tubules of the digestive diverticula. Mucous secreting and eosinophilic epithelial cells occur in varying numbers along the course of the tract. Phagocytes are present between the lining epithelial cells, among the peripheral collagenous and muscle fibers, as well as in the lumen of the tract. The gastric shield is shown to be intimately attached to the underlying epithelium by a central clip as well as by minute cytoplasmic processes. The anatomical relationships are compared with various lamellibranchs including the Chilean oyster, Ostrea chilensis Philippi; the European oyster, Ostrea edulis L.; and the Portuguese oyster, Gryphea angulata Lamarck.