抄録
Grapsid crabs Hemigrapsus sanguineus infested with Sacculina polygenea were reared in isolation for a maximum of 232 days. Size, colour and morphological features of externae were examined daily. After repeated spawning externae dropped off and new externae appeared. Of a total of 41 newly appeared externae 15 erupted more than 40 days after moulting of host crabs. Ten externae erupted within 3 days after the moult. The externae released nauplii with an average interval of 17.0 ± 2.6 days. Moulting of the inner cuticle of the mantle cavity of the externa occurred 6.2 ± 4.0 days after the release of nauplii. The behaviour of parasitized H. sanguineus at the time of nauplii release was observed. The crabs climbed up on a stone placed in an aquarium and raised their bodies supported by walking legs and chelipeds. The fourth legs were always extended backward. Low frequency pumping movements of the abdomen contributed little to larval release. The nauplii were mainly expelled from the aperture by the contraction and expansion of the externa.
