Comparative Study of the Intraperitoneal Alimentary Tract of Parasitic and Nonparasitic Lampreys from the Great Lakes Region

Abstract

The macroscopic and microscopic anatomy of the intraperitoneal alimentary tract of two parasitic species of lamprey, Petromyzon marinus and Ichthyomyzon unicuspis, and two nonparasitic species, Entosphenus lamottenii and Ichthyomyzon fossor, are described and compared. In adults of both parasitic species a diverticulum of the anterior mid-gut occurs at the level of the posterior oesophagus; and longitudinal mucosal folds or rugae greatly increase the internal surface of the mid-gut. The course of the mid-gut spiral valve shows species variation, and is more complex in parasitic than nonparasitic adults. Throughout most of the tract tall cilia occur on epithelia over the tips of folds, whereas short cilia form tracts in the fornices. Extra-epithelial tunics are composed of fibro-elastic connective tissue, circular smooth muscle, and a serosa. The four species can be distinguished on the bases of the mucosal folds, spiral valve, and the lining epithelium of the oesophagus.Atrophy of the tract of both parasitic species commences with the spawning migration, when the epithelium exhibits a characteristic cytolysis with vacuolation of the cytoplasm and peripheral migration of the nuclei. In Entosphenus lamottenii atrophy involves initial necrosis of the epithelium and subsequently of the extra-epithelial tunics, both accompanied by massive infiltration of lymphocytes, whereas in Ichthyomyzon fossor it is resultant upon autolysis of some of the epithelial cells with progressive reduction in the diameter of the tract without interruption of the lining layer.