Two new interstitial evtheroid ostracods are described from a small sandy beach in Shimoda, central Japan: Microloxoconcha ikevai sp. nev. (Cytheromatidae) and Parvocythere japonica sp. nov. (Parvoeytheridae). This is the first record of the genus 1]arvocythere Hartman, 1959 from Japan. By sampling every two months through a year along a transect extending from the shoreline landward across the study area, the optimal zone for each species was found. The peaks of individual density for ML ikeyai and P, japonica lie seaward and landward, respectively. Both species show a wide tolerance to changes in salinity, but they do not live where fine sand (mode of grain size less than lf8mm) is the dominant particle size. In assays of phototaxis, M. ilteyai, which has a naupliar eye, showed negative phototaxis.

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Four interstitial cobanocytherid species are described from central Japan: Cobanocythere ikeyai sp. nov., Cobanocythere lata sp. nov., Paracobanocythere watanabei sp. nov. and Paracobanocythere grandis sp. nov. The reports of the two new Paracobanocythere species are the second and third for this genus since the original description of P. hawaiiensis Gottwald, 1983. Cobanocythere ikeyai sp. nov., and C. lata sp. nov., from Japan are morphologically more similar to the species of the “lanceolata group” by Gottwald (1983) and C. guttaeformis Gottwald, 1983 from the Galapagos Islands, respectively, rather than to other Cobanocythere species from Japan. The Japanese archipelago (eastern Eurasian Continent) and the Galapagos Islands (north-western South America) are separated by about 15,000 km from each other, and have never been adjoined throughout geological history. This fact, and also the morphological similarities between Cobanocythere species from Japan and the Galapagos Islands, suggests that this genus may have undergone global dispersal at several times in the past. Conversely, the genera Cobanocythere and Paracobanocythere are distributed not only around continents and continental islands but also around oceanic islands such as the Hawaiian and Galapagos Islands. We conclude, therefore, that the cobanocytherids seem to have been able to disperse long distances across oceans.

In the original description, the interstitial ostracod genus Microloxoconcha Hartmann, 1954 was diagnosed by the morphology of its carapace and the number of segments in the antennula, antenna, and mandibula; these characters, however, are firequently shared with other taxa. The genus is therefore redescribed with special emphasis on the hinge morphology, antennula form, and large seventh limb. Furthermore, two new species of this genus are described: M schornikovi sp. nov. from sandy beaches of the Miura Peninsula, central Japan, and M. kikaijimaensts sp, nov. frem Kikaijima Island, Amami Islands, southern Japan, New descriptive terminology is proposed for structural details of the male copulatory organ of Microloxoconcha,