Reproduction of Anoplodium hymanae, a Turbellarian Flatworm (Neorhabdocoela, Umagillidae) Inhabiting the Coelom of Sea Cucumbers; Production of Egg Capsules, and Escape of Infective Stages without Evisceration of the Host

Anoplodium hymanae, a member of the turbellarian family Umagillidae, parasitizes the holothuroid Stichopus californicus along the northeastern Pacific coast. As in several other species of Anoplodium, egg capsules are released into the perivisceral coelom of the host. The egg capsules of A. hymanae become ensheathed by host coelomocytes and are then accumulated in masses that are usually about 1 mm in diameter. A single mass from a host that is moderately infested by Anoplodium may contain up to several hundred egg capsules. The masses pass out of the host on a daily basis, presumably through previously undescribed ducts that connect the coelom to the lumen of the posterior end of the rectum. Some masses of coelomocytes with egg capsules may be released if the host eviscerates but, contrary to previous hypotheses, evisceration is not required for completion of the life cycle. Anoplodium hymanae continues to grow after attaining reproductive maturity. The size of the egg capsules, and thus of the larvae, varies with the size of the parent worm.