稀少なクシクラゲの1種Lobatolampea tetragona の小型成体および未成熟個体の形態

Abstract

Five nearly intact specimens of a rare ctenophore, Lobatolampea tetragona Horita, including one small adult specimen with four C-shaped gonads in the pharyngeal plane and four immature specimens without gonads, were collected on 22-26 April 2008 at a fixed site along the wharf at Tomari Port, Naha City, on Okinawa Island, Japan. Collections were made by vertical hauls of a small plankton net from a depth of 7 m 3-6 times per day, 10-20 hauls each time for a total of 290 hauls, between 05:45 hr at the earliest and 21:30 hr at the latest. Four other specimens taken in these hauls were too damaged for detailed observation. These individuals are the first specimens of this species under 10 mm in minor-axis length ever recorded, and morphological observations show that metamorphosis from the juvenile form is nearly complete by the time the body's major-axis length has reached 6.5 mm. Furthermore, in the intermediate developmental stage between juvenile and adult, hitherto unreported filiform ide branches are present on the secondary tentacles, the side branches being yellow in color and becoming globular when contracted. During a short period of laboratory culture, damaged ody parts of some specimens were quickly repaired and secondary tentacles were regenerated.