カギノテクラゲ属の1種(刺胞動物門, ヒドロ虫綱, 淡水クラゲ目)の成長と触手先端部の2種類の運動

Abstract

A young medusa (0.5 mm in umbrella diameter) of Gonionemus sp. with 12 tentacles, manubrium protruded from the umbrella aperture, four statocysts and roundish-conical adhesive pads on oral side of all tentacles was collected from a jellyfish rearing tank on July 17th, 2015. It was kept in a petri dish fed with Artemia nauplii and fillets of sea bass, changing sea water twice in a day. From the 1st day of rearing the medusa waved tentacle tips like rattlesnakes' tails. Strong vibration with bending and stretching of tentacle tips was observed on and after 25th day. These movements resembled swimming or writhing lugworms, suggesting the medusa attracts fishes as angler fishes do. White tissues appeared in the mesoglea around radial and ring canals on the 16th day. A mouth developed into four oral lips on the 17th day. On and after the 27th day many spots of reddish brown pigments were observed on the umbrella margin. On the 107th day a bunch of large cilia was noticed on a tentacle tip. A peduncle developed about one third of the umbrella height by the 112nd day. Gonads developed well by the 134th day, but spawning had never been observed. On the 175th day tentacles had increased up to 106 in number, however only 25 statocysts existed. The umbrella diameter had reached 11.0 mm on the 187th day. The 2nd manubrium was found on one out of four gonads on the 187th day. The present medusa had many common morphological and behavioral traits with medusae of Moerisia horii, suggesting kin relationships between Limnomedusae and some members of Moerisiidae.