日本海産ハナクラゲモドキMelicertum octocostatum(軟クラゲ目, ハナクラゲモドキ科)の成熟クラゲ

Abstract

A living mature female medusa of Melicertum octocostatum (M. Sars) (Leptomedusae, Melicertidae) was collected in the Sea of Japan off the coast of Yamagata Pref., northern Japan in June, 2003. This specimen serves as the basis for the first description of this developmental stage of this species in Japan. The morphology, cmdome on the tentacles and oral lips (atnchous isorhizas and microbasic mastigophores), and egg size (mostly 104 urn in diameter) of this medusa are described, and occurrence records of 23 other medusan specimens of this species from the same area in Yamagata Prefecture are given. In comparison with 7 other described specimens from two localities in northern Japan (Hokkaido and Aomon Pref.), the present specimen is the largest (15.1mm in both diameter and umbrellar height) and has the most numerous tentacles (at least 80 large tentacles and a nearly equal number of small tentacles). Two individuals of a parasitic trematode were found in the mesogloea of the female medusa.

山形県沿岸から2002年と2003年に計24個体のハナクラゲモドキを観察・採取した.その内の雌1個体の外部形態,刺胞相,卵の直径を記載する.本種の成熟個体の記載は日本からは初めてとなる.この雌個体は,これまで北日本(2地点)から報告されているどの7個体よりも大きく,傘径と傘高はともに15.1mmあり,また最大数の触手を備えていた(よく発達した少なくとも80本の触手に加えてほぼ同数の小型の触手).触手や口唇に装填される刺胞(無棟型等根体と短床型有鞭体の2種類)と体部位ごとのそれぞれの刺胞の大きさを記載した.また,放卵された未成熟卵の直径は,通常104/µmであった.