THE MORPHOLOGY AND LIFE CYCLE OF THE TREMATODE HIMASTHLA QUISSETENSIS (MILLER AND NORTHUP, 1926)

¹ From the Marine Biological Laboratory, Woods Hole, Mass. and the Biological Laboratory, New York University

Cercaria quissetensis Miller and Northup, 1926 has been restudied. It is the only echinostome cercaria which has been found in the examination of over 18,000 specimens of Nassa obsolela at Woods Hole. This cercaria encysts in the gills, mantle and foot of various mollusks. Metacercariæ were obtained experimentally in Mya arenaria, Modiolus modiolus, Mytilus edulis, Cumingia tellinoides, Pecten irradians, Ensis directus, and Crepidula fornicata. The metacercariæ are infective for birds three days after encystment and develop to maturity in the herring gull, Larus argentatus. Sexually mature specimens are identical with certain of those described by Linton (1928) as Himasthla elongata (Mehlis). Since there are important differences between the present specimens and H. elongata, they cannot be referred to that species and the name of the cercaria is adopted for them. Possible synonymy in the genus Himasthla is discussed.