Abstract
The annual cycle of the testicular structure of Actinia equina in Japanese waters was investigated by histological observation. This is the first study concerning the reproductive biology of this species in Japan. Specimens of A. equina were collected once a month from two intertidal rocky shores in eastern Sagami Bay, from January, 1991, to June, 1991, and from April, 1993, to January, 1994, respectively. Most of the specimens were male or non-sexual individuals and there were few females with mature oocytes. Spermatogenesis starts from late fall to early spring and the testicular cysts mature in mid-summer. This indicates that the spawning season of A. equina is mid-summer and sexual reproduction may occur in the summer. Although young are found in the enterons of adults of both sexes all year round, the source of these young remains unknown.
