INFECTION OF NEW HOSTS BY ANOPLODIUM HYMANAE, A TURBELLARIAN FLATWORM (NEORHABDOCOELA, UMAGILLIDAE) INHABITING THE COELOM OF THE SEA CUCUMBER STICHOPUS CALIFORNICUS

¹ Department of Zoology, University of Washington, Seattle, Washington 98195

Anoplodium hymanae, a member of the turbellarian family Umagillidae, parasitizes the holothuroid Stichopus californicus in the N. E. Pacific. Experiments revealed that the life cycle is direct, and that encapsulated embryos are the infective stage. Embryogenesis may or may not be completed by the time egg capsules pass out of the host of the parent worm. Developed embryos can survive in their capsules for 10-11 months, but they die if the capsules remain in sea water indefinitely. Hatching occurs when egg capsules that contain developed embryos are ingested by a sea cucumber; hatching is induced by the host digestive fluids. Larvae reach the coelom by penetrating the wall of the lower intestine or, more commonly, the wall of the respiratory trees. Larvae of A. hymanae and those of intestine-inhabiting umagillids differ in behavior, but appear similar in morphology. The size of worms infesting S. californicus varies seasonally and is correlated with the seasonal feeding behavior of the host.