退化しないクラゲ口柄基部より走根を伸張しポリプに若返ったベニクラゲ(ヒドロ虫綱, 花クラゲ目)の成熟雄

Abstract

A mature male medusa (small morphotype) of Turritopsis nutricula McCrady collected on 18 August 2005 from Tanabe Bay, Wakayama Prefecture, Japan, transformed to the young polyp stage after partial degeneration of the medusa body, by extension of stolons from the base of the undegenerated manubrium, which retains the ability to engulf and digest food (Anemia nauplii). Such a reversion, retaining part of the old body (the manubrium) attached to the new body (the polyp colony), is the first such example known in the life cycle of this species. Before undergoing this transformation, the male medusa had fertilized the ovum of a simultaneously collected mature female medusa cultured together with it, and a planula was produced. This male thus led a dual life, not only reverting to the youthful stage of the same genotype, but also producing an offsprng of a different genotype.

ベニクラゲの成熟雄クラゲ(和歌山県田辺湾産の小型)の口柄を除く体全体が退縮後に, 生残した口柄(餌のアルテミア幼生の断片を飲みこみ消化できる)の根元から走根を教本伸張し, ポリプへ形質転換するというユニークな若返りを世界で初めて観察したので記録する.この雄と同時に同じ地点から採集された1個体の雌クラゲより, 飼育後2日目に放出された3卵のうちの1卵が, 1日でプラヌラ幼生に育った従って, この雄クラゲは, 有性生殖を行うと同時に自らも若返ったことになる.