A New Form of the Bivalve-Inhabiting Hydrozoan Eutima japonica (Leptomedusae, Eirenidae) in Japan

Abstract

Further intraspecific variability of Eutimajaponica is described and illustrated. The newly matured medusa of this so-called "transitional" form, the hydroid of which is associated with the bivalve Barbatia virescens from Kashima Island off Kyushu, southern Japan (53.8% prevalence), is more developed than the medusa of the intermedia form, but is less developed than the medusae of the southern and northern forms. The major morphological features of the new form's newly matured, 7- to 14-day-old medusae of both sexes are: a very short peduncle of only 0.3-1.5 mm in length, four (61.7% ofindividuals) or eight (34.0%) tentacles, a medium-sized umbrellar diameter (4.8-7.4 mm), and a large but variable number (0-67) of lateral cirri. The life-span of the medusae in the laboratory at 22 ± l℃ was relatively short, about one month.