THE MORPHOLOGY AND LIFE HISTORY OF THE DIGENETIC TREMATODE, ZOÖGONOIDES LAEVIS LINTON, 1940

Linton (1940) described the adult stage of Zoogonoides laevis and distinguished between this species and Z. viviparus (Olsson, 1868) Odhner, 1902, the type and only other known representative of the genus. He found the worms in the intestine of Tautoga onitis and an immature specimen from the round herring, “? Etrumensadina― (= Etrumeus teres) was referred provisionally to Z. laevis. During the summer of 1942, tailless cercariae were found emerging from Columbella (= Mitrella Rizzo) lunata collected in the Woods Hole region. -Their striking resemblance to the cercariae of Zoogonus lasius (Leidy, 1891) Stunkard, 1940 indicated that the two were closely related. Furthermore, their morpho logical agreement with Zoogonoides laevis suggested that they might be larvae of the latter species. Experiments demonstrated the correctness of the hypothesis and the successive stages in the life cycle have been obtained. The cercariae develop in sporocysts in the lymph spaces of C. lunata, penetrate into Nereis virens where they become metacercariae, and sexual maturity is attained in the intestine of T. onitis. The eggs are large, without shells, and contain active, ciliated miracidia when extruded. The larvae hatch in sea water and invade the snails where the asexual generations are produced. The life history was reported in abstract (Stunkard, 1942).