Three new species of dicyemid mesozoan are described from Octopus kagoshimensis Ortmann, 1888 collected off Irino in Tosa Bay, sourthern Shikoku, Japan. Dicyema tosaense sp. nov. is a small species that reaches about 800μm in length. The vermiform stages are characterized by 16-18 peripheral cells, a conical calotte, and an axial cell that extends to the base of the metapolar cells. Infusoriform embryos consist of 37 cells; two nuclei are present in each urn cell and the refringent bodies are solid. Dicyema irinoense sp. nov. is a species of medium size that reaches about 1300μm in length. The vermiform stages are characterized by 22 peripheral cells, a discshaped calotte, and an axial cell that extends to the base of the propolar cells. Infusoriform embryos consist of 37 cells; a single nucleus is present in each urn cell and the refringent bodies are solid. Dicyema sphaerocephalum sp. nov. is a species of medium size and reaches about 1000μm in length. The vermiform stages are characterized by 18-20 peripheral cells, a rounded calotte, and an axial cell that extends to the base of the propolar cells. Infusoriform embryos consist of 37 cells; two nuclei are present in each urn cell and the refringent bodies are solid. This is the first report of dicyemids in the octopus O. kagoshimensis.

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A new harpacticoid copepod, Amphiascus kawamurai sp. nov., is described from a tank for nori (laver) cultivation on the shore of Ariake Bay, Japan. This species belongs to the pacificus-group of Amphiascus and is most closely related to A. parvus Sars, 1906, which is briefly redescribed based on Sars' original material. The two species are distinguishable by spinules on the genital double-somite and by leg 5 of the female. Specimens previously described as A. parvus from the Red Sea and Argentina are shown to be not identical to Sars' A. parvus. The new species is the second member of the genus from Japan.

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Upogebia rupicola, a new species of upogebiid shrimp from Okinawa Island, Ryukyu Islands, lives in burrows made in siltstone substrates in the intertidal zone. It is similar to U. carinicauda (Stimpson, 1860), widely known from the Indo-West Pacific, but is distinguished from the latter by the structure and armament of the first pereopod and the armament of the lateral ridge of the anterior carapace.

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The Japanese assassin bugs of the subfamily Reduviinae are revised. Six species in four genera are recognized, including two new species, Reduvius yaeyamanus and Tiarodes miyamotoi, both from Ishigaki Island and Iriomote Island in the Ryukyu Islands. The four previously known species are diagnosed. A key is given for the separation of the Japanese genera and species of the Reduviinae.

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To resolve the controversial taxonomic status of two closely-related lanternfishes, Diaphus perspicillatus (Ogilby, 1898) and D.gigas Gilbert, 1913, mitochondrial cytochrome b (cyt b) gene sequences of representative individuals were obtained, and specifically-diagnostic restriction sites investigated. In the 5'-half nucleotide sequences of the cyt b gene (594 bp), a relatively high level of nucleotide substitution between the species (8.2-8.7%), together with very low intraspecific variation (<0.86%), was observed, which clearly indicates the two morphs to be specifically distinct. Previous hypotheses regarding gigantism of D.gigas and suspicions regarding the synonymy of the two species are rejected. The nucleotide sequences and practical restriction enzyme assay indicate that any one of four restriction endonucleases (Fok I, Hae III, Nla IV, and Rsa I) can unambiguously discriminate between the two species. Based on specimens identified by molecular analysis, eye diameter and gill raker count were found to be good diagnostic morphological characters.

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