A new species of marine cercaria Cercaria itoi sp. nov. from the spindle shell Fusinus perplexus from Kanagawa Prefecture, Japan.

A new species of marine cercaria, possibly belonging to the family Acanthocolpidae, was found in the digestive gland of the spindle shell Fusinus perplexus and the specific name Cercaria itoi is proposed. C. itoi is a distome and biocellate cercaria with a long simple tail, five pairs of penetration gland cells, I-shaped excretory vesicle, 66 flame cells on each side and peculiar structures of comma- to sausage-shaped minute bodies, probably cystogenous glands, filled in the hindbody posterior to the acetabulum. The cercaria develops in redia, but its maturation of the cercaria occurs in the digestive gland of the host, after the immature cercariae leave the redia.