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

Abstract

Cercaria quissetensis was restudied. It is the only echino-stome cercaria which has been found in the examination of over 18,000 specimens of Nassa obsoleta at Woods Hole. This cercaria encysts in the gills, mantle and foot of various mollusks. Metacercariae were obtained experimentally in Mya arenaria, Modiolus modiolus, Mytilus edulis, Cumingia tellinoides, Pecten irradians, Ensis directus, and Crepidula fornicata. The metacercariae are infective for birds 3 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. 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.