本種の日本最南端分布海域で1世紀ぶりに採集された大型のベニクラゲ(ヒドロ虫綱, 花クラゲ目)

Abstract

Many (25 individuals) immature medusae of a large form of Turritopsis medusae were collected from Enoshima, Kanagawa Prefecture in April, 2016, and cultured in the laboratory for about two months until their death (rejuvenated from a medusa to stolon, but no formation of zooids). They grew well-grown (maximally 8 mm in umbrella height) medusae with scarlet-coloured manubrium and c 80-100 tentacles. The present occurrence of a large form, though not an adult, is the second southernmost distributional record of this species after one century. However, the number of tentacles of the present medusae showed the minimum number, in contrast to having much more tentacles in wild medusae collected from various places in Japan (from Kanagawa Prefecture to Hokkaido).

神奈川県江ノ島稚児ヶ淵周辺で25個体のベニクラゲ類の未成熟クラゲを2016年4月に採集し，その日から一定条件下で約2箇月間，死亡(走根化したが個虫形成なし)に至るまで飼育した．その結果，口柄が紅色で，最大の傘高8 mm程度，80-100本程の触手を有する大型のベニクラゲに成長した．従って，本採集記録は，成体ではないが，本種の日本最南端分布海域で１世紀ぶりの出現記録となった．しかし，本個体の触手数は日本各地(神奈川県から北海道まで)の野外採集個体と比べて最少であった．