A new species of Pachycordyle (Hydrozoa, Clavidae) from Lake Biwa (Japan),with remarks on this and related Clavid genera

The history of research on species of Pachycordyle and related genera is di scussed. A description and differential diagnosis of a new species, Pachyco rdyle kubotai, is presented. Hydroid colonies, hydranths, and gonophores of this species are described in derail. Peculiarities of medusoid developmen t and oocyte maturation are analyzed. The genus Pachycordyle is rediagnosed and an identification key to species assigned to it is provided. Clavopsel la is regarded as congeneric with Pachycordyle. Thieliana is established as a new genus for species subsequently and erroneously assigned to Clavopsel la. The taxonomic status of species referable to Thieliana is discussed, ju stification is provided for our position that these genera belong to the fa mily Clavidae. Characteristics of genera assigned to the family Clavidae ar e summarized. Data on the geographic distribution and ecology of the specie s of Cordylophora, Pachycordyle, and Thieliana, referred here to the subfam ily Cordylophorinae, are presented.