The ant genus Myrmicaria from Southeast Asia is clearly divided into two distinct species-groups (the M. arachnoides and M. brunnea groups) based on their morphology and nesting behaviour, as was suggested by Emery in 1922. We have found many additional characters, not noticed by previous authors, that differentiate the two groups. Male genital characters have also proved useful, not only in defining the groups but also in discriminating species in some cases.
Two estuarine species of the hermit crab genus Clibanarius are recorded for the first time from the Ryukyu Islands, southern Japan. The occurrence of Clibanarius demani Buitendijk, 1937 in Okinawa Island represents a new addition to the Japanese fauna and greatly extends its distributional range to the northeast. Clibanarius infraspinatus (Hilgendorf, 1869) is broadly distributed in the Indo-West Pacific including the mainland of Japan, but there have been no definite records from the Ryukyu Islands until the present report. A brief note on the species of Clibanarius recorded from the Ryukyu Islands is provided, along with a key to these species.
The poorly known porcellanid crab Lissoporcellana miyakei Haig, 1981 is reported for the first time from Japanese waters. The present specimen greatly extends the geographical range of this species to the northeast. The fresh coloration of L. miyakei is depicted for the first time in a photograph. In addition to morphological characters, L. miyakei differs from L. nakasonei (Miyake, 1978) in coloration.
Thalestris hokkaidoensis sp. nov. (Crustacea: Copepoda: Harpacticoida: Thalestridae) is described from Uchiura Bay, Hokkaido, Japan. The species infests the red alga Palmaria palmata (Linnaeus) Kuntze, living in galleries it makes in thalli. Thalestris hokkaidoensis is distinguished from congeneric species by the structure of P1 and P5.
A new naidid oligochaete, Nais kisui, is described from oligohaline habitats in northern Japan. This new species is similar to N. borutzkii Sokolskaya, 1964, a species known from Far Eastern Russia, in that both species have sigmoid needle chaetae in the dorsal bundles and protrusible projections of the spermathecal ducts, which in both species are set in deep chambers created by infoldings of the body wall. However, N. kisui differs from N. borutzkii in having inconspicuous male efferent ducts, each with a conical penis that opens into a median male bursa.
Collections of freshwater planarians made by two expeditions to the Kuril Islands and Kamchatka are described, thus providing the first comprehensive account of the occurrence of this group of animals in the Kuril Archipelago. The samples contained three species: Seidlia schmidti (Zabusov, 1916), S. elongata (Zabosova, 1929), and Phagocata sp. The new records for S. schmidti and S. elongata include asexual specimens that were identified on the basis of their eye arrangement. This study shows that freshwater planarian species that were already known to occur in Kamchatka and Japan have also colonized the Kuril Islands. Possible scenarios for dispersal into the Kuril Islands from two mainland source areas during the Last Glacial Maximum are discussed.