Sagitta as a Host of Larval Trematodes, including a New and Unique Type of Cercaria

Abstract

IT has long been known that Sagitta may occasionally foster young trematodes, but we have learned very little since Müller, Busch, Leuckart and Pagenstecher made discoveries of this kind more than one hundred years ago. During the present century, Miss M. V. Lebour found two species of Digenea in Sagitta bipunctata ¹. Small Derogenes various (Hemiuridae) were seen near the ovary, generally singly, and post-larval Opechona bacillaris (Allocreadiidae) were seen in the gut as well as near the ovary, indicating that migration into the cœlom takes place through the wall of the intestine. Young forms similar to Derogenes have been found in the body cavity of unspecified chætognaths in South Australia, and small yellow cercariæ in the cœlom of Sagitta enflata were recorded but not described. Small appendiculate Hemiurids have been seen in S. elegans at Woods Hole and in S. enflata from the Bay of Algiers, and forms identified as small Hemiuris communis have appeared in S. elegans and S. setosa from Northumbrian plankton. Young forms of a rarer trematode—some unnamed member of the Accacoeliidae and possibly a species of Tetrochetus—have been found in S. enflata from the Indian Ocean near Madras².