THE METAMORPHOSIS OF THE ANTHOMEDUSA, POLYORCHIS KARAFUTOENSIS KISHINOUYE

Abstract

One of the highest Anthomedusa, Polyorchis karafutoensis was first described by KISHINOUYE (1910) from Sakhalin. Since then the medusa was sometimes reported from the southern coast and the eastern lagoon of Sakhalin and the eastern part of Hokkaido, Japan by UCHIDA (1925, 1927, 1940). However, its life history remains mostly unknown, as also in other members of the genus Polyorchis except for the fragmental records of the medusan development in P. penicillatus by FEWKES ( 1889) and FOERSTER (1923), in P. karafutoensis by UCHIDA (1927) and in P. montereyensis by SKOGSBERG ( 948). In Akkeshi Bay Polyorchis karafutoensis is commonly found from middle April to late July. The early development of this species was previously reported by the author (NAGAO, 1963). In the present paper the metamorphosis and the growth in the medusan stage are dealt with. The medusae were collected in Akkeshi Bay and in Akkeshi Lake which is a lagoon and is directly connected with the bay ( cf. UCHIDA et al., 1963). The medusae were collected by surface tow every week on the average during April - July in 1963 and 1965. In the later season when the medusae grow larger they were scooped with a net. Umbrellar form, ocelli, size and other living characters of the medusae were recorded before preservation. Before proceeding further the author wishes to express his sincere thanks to Prof. Emer. Tohru UCHIDA and Prof. Mayumi YAMADA, Hokkaido University, for their kind guidance and encouragement.