Three marine cercariae in the clam Tapes philippinarum from Lake Hamana, Japan: morphology and level of infection.
Of 3200 T. philippinarum obtained from Lake Hamana, Japan, between March 1981 and January 1982, 110 were infected with Cercaria pectinata, 3 with C. tapidis and one with another Cercaria sp. C. pectinata is a yellowish, non-oculate, trichocercous, fellodistomid cercaria developing in large saccular sporocysts in the host gonad. C. tapidis is an oculate cercaria with a tail 5 times body length, and the other species is a non-oculate, furcocercous, gymnophallid cercaria. C. pectinata was more prevalent in September to March (2.0 to 3.6%) than from May to August (0 to 1.2%). Early sporocysts were present in inter-follicular spaces of the gonad where they grew and eventually occupied the greater part of the gonad. Sporocysts with numerous mature cercariae were seen from March to April.