瀬戸内海におけるカイヤドリヒドラクラゲ(ヒドロ虫綱, 軟クラゲ目)の分布初記録

Abstract

In September 2004, one of the most derivative species of bivalve-inhabiting hydrozoans, Eugymnantheajaponica Kubota, was for the first time found in the Inland Sea of Japan. Male and female mature medusae were collected by plankton towing at Mitsushama harbor, Matsuyama City, Ehime Prefecture. The hydroids were also found, associated with Mytilus galloprovincialis collected from the same harbor, and their medusae were obtained by culture. The diagnostic characters of this species are confirmed and described. Based on successive research on distribution of the hydroids and medusae in various places, particularly at Mitsuhama harbor and its adjacent area in the Inland Sea of Japan since 1978, it is conceivable that the present species is distributed in this area very recently.

2004年9月下旬に, 瀬戸内海から初めてカイヤドリヒドラクラゲEugymnantheajaponica Kubotaのポリプとクラゲを発見した.愛媛県桧山市三津浜港で, 雌雄の成熟クラゲをプランクトンネット曳きで採集し, クラゲ芽を形成したポリプがムラサキイガイと共生するのも採集したこのホストより取り出したポリプを飼育して成熟クラゲを得, それらのクラゲの形態も観察し, 野外から採取したものと同じであることを確かめ, まとめて記録した. 1978年以降言頼戸内海沿岸各地, 特に三津浜港とその近郊での継続的なポリプとクラゲの分布調査から, 本種は, ごく最近に本海域に分布するようになったと推察される.