The complete larval development of Helice formosensis was obtained in the laboratory. It consisted of 5 zoeal and 1 megalopa stages before moulting to the first crab instar on the 47th day at a water temperature of 15-22℃. The morphology of the larvae is described in detail and comparisons are made with larvae of other species of Helice.
A new species of harpacticoid copepod, Bryocamptus yohteiensis, is described. Specimens of this new species were collected from puddles on the streamside of a willow grove in Kutchan, located on the north of Mt. Yohtei in Hokkaido, Japan. The species is close to B. umiatensis Wilson, 1958 known from Alaska, Kamchatka, and Sakhalin Island. This is the seventh species of the genus reported from Japan.
Three species of the marine mite genus Actacarus occurring on the coast of Hokkaido, northern Japan, are described. Actacarus pacificus Bartsch was found in the subtidal zone of Teuri Island ; this species is recorded from the northwestern Pacific for the first time. Actacarus illustrans Newell was taken from the intertidal zone in Oshoro Bay, the Sea of Japan. A new species, A. octosetus, is described on the basis of specimens from intertidal sandy sediment in Uchiura Bay, southern Hokkaido. The new species is easily distinguished from its congeners in having 4 pairs of perigenital setae in the female and 34-40 perigenital setae in the male. Marine suctorians are associated with A. octosetus. A key to the Actacarus species in Hokkaido is given.
Pycnogonid material from New Caledonia and the Great Barrier Reef has been examined. Callipallene ersei sp. nov. is described from the infralittoral sand of New Caledonia. Specimens from both regions have allowed the reassessment of Anoplodactylus species with more than 10 cribellate cement gland pores per femur : all (other than A. laciniosus Child, 1995) are assigned to A. cribellatus Calman, 1923, including A perforatus Nakamura and Child, 1982 and A. simplex Clark, 1963 as junior synonyms.
A new genus, Idatenopsocus, represented by Idatenopsocus orientalis (Vishnyakova, 1986), comb, nov., is described and the species is redescribed. Within the family Mesopsocidae, this new genus is considered as the sister group of a monophyletic group composed of the genera Mesopsocus, Microtrichipsocus, Metapsocus, Cyrtopsochus, Hexacyrtoma, and Rhinopsocus.
A systematic revision of the osmerid genus Hypomesus Gill, based on a detailed analysis of external and internal morphological characters, revealed the presence of six species, one of which is described as new. These six species fall readily into three species-groups : the Hypomesus nipponensis group, containing H. nipponensis McAllister, H. chishimaensis new species, and H. transpacificus McAllister ; the H. olidus group, containing only H. olidus Pallas ; and the H. japonicus group, containing H. japonicus Brevoort and H. pretiosus Girard. Synonymies, diagnoses, and descriptions are given for all taxa, geographic distributions are described and plotted, and a key to the species of the genus is provided.
The flabellinid nudibranch Chlamylla atypica (Bergh, 1899) is described and illustrated based on more than 200 specimens collected from the Sea of Japan coast of Hokkaido, Japan. Notes on the diet, reproductive system, and prey-related colour differences are also given. The present record constitutes a southward range extension for the species.