General patterns of the microdistribution of some interstitial animal groups are described as a preliminary report from the studies on the interstitial fauna and the bionomics of harpacticoids, which have been carried out at the Ishikari beach on the Japan Sea coast of Hokkaido. The Ishikari beach is characterized by homogeneous medium fine sand and small tide. Vertical distribution of nematodes are examined in order to estimate the difference between the density as represented by the number of individuals per unit sample volume and that per unit pore water volume by using the method formerly elaborated by the author. Characteristics in the microdistribution of Hesionides arenaria (Polychaeta) and Hypsibius itoi (Tardigrada) and five species of Harpacticoida are discussed. Distribution range of Arenopontia ishikariana, that is the dominant species in this beach (the maximum density recorded 4045 individuals per 100 cc sand sample), is very wide both horizontally and vertically, extending from the foreshore to the backshore. Nodtiella sp. penetrate into the backshore a little above the ground water level. Arenosetella bidenta and Leptastacus japonicus occur within well wet sand of the foreshore, and do not penetrate into the backshore. Paraleptastacus unisetosus are restricted in deep layers of the backshore during the summer, but appear in the upper foreshore during a short period of the early spring. This change of the microdistribution of P, unisetosus suggests a seasonal migration.

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Three species of interstitial harpacticoid copepod (Phyllopodopsyllus punctatus, P. setouchiensis and Oniscopsis inabai) are characteristic inhabitants at the upper shore of Mukaishima Island in the Inland Sea of Japan. These species occurred jointly in the narrow zone, but their center of distributions were delicately separated. The depth distribution of each species in the sediment and their seasonal and diurnal migrations were investigated. Each species had characteristic depth-distribution pattern, and their relative positions were unchanged throughout most of the year irrespective of vertical seasonal mi.gration. P. punctatus, dweller of the shallow layer, made clear seasonal shift to the deeper layer in winter, but the tendency was not so obvious in other two deeper zone dwellers. Two Phyllopodopsyllus species made slight vertical movement during one daily tidal cycle, moved toward surface at ebb tide and toward deeper at flood tide. Some physical properties of the sediment were measured, but none of them positively correlated with species specific distribution patterns. Positive evidence of interspecific competition was not observed. To elucidate difference of species specific distribution by biological nature of the sediment, a series of choice experiments was carried out. Each harpacticoid species showed positive preference to the sand of the depth in which the species highly populated. It is suggested that the species specific preference to the organic film on the surface of sand grains may be one of the factors inducing microhabitat segregation within the sand-dwelling copepod community.

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A feeding classification scheme of free-living marine nematodes devised by Wieser (1953) is presented for ecological studies of the nematode assemblages as a valuable analytical tool. The classification is based upon the structure of the buccal cavity and each of the feeding types, 1A (selective deposit feeders), 1B (non-selective deposit feeders), 2A (epigrowth feeders), 2B (predators/ omnivores), is speculated to utilize different food resources. Their relative proportions in a nematode assemblage depend upon the nature of the available food connected with other environmental factors in the habitat. The change of these proportions is believed to indicate the variation of the environmental conditions.

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Post-embryonic development and seasonal distribution of developmental stages of marine Ostracoda (Podocopina and Myodocopina) are briefly reviewed. Since studies on the former are one of the first steps required for the bio-ecological investigations, information for precise identification of developmental stages is described. On Myodocopina, total number of larval stages and a key to early instars are presented. According to Theisen (1966), life histories (seasonal distribution of developmental stages) of some species are summerized in tabular form.

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Isopod Crustaceans consist of 9 suborders and about 5000 Recent species are hitherto reported all over the world. Morphological features of those suborders and the present situation of taxonomic study are briefly reviewed. About 260 species belonged to 8 suborders are reported from Japan and adjacent waters. In Japan, taxonomic study of both marine and terrestrial isopods is still in undeveloped state, much increase of species number is expected in future.

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Growth, survivorship of immature animals and breeding activity in Jesogarrmarus sp, were studied at 9°C, 14°C and 19°C in the laboratory. Growth rates increased with temperatures in isolated condition but decreased in group animals. Initial mortality was highest in 19°C and survivorship was low in group animals than in isolated animals. Breeding was least successful in 19°C in terms of the release of young per female breeding cycle as well as the number of young released per brood. It was concluded that the upper critical temperature for the population of Jesogammarus sp, lay at about 19°C.

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Reproductive traits of three species of caprellids attached to the annual Sargassum horneri were studied by monthly sampling throughout the year in Amakusa, west Kyushu. For three species (Caprella tsugaruensis, C, danilevskii and C, decipiens), some ecological characters such as individual growth and number of molting, sexual dimorphism, 50% maturity size of female, the clutch size - female body size relation etc., and their seasonal variations were examined. Seasonal fluctuations of host algal biomass and that of caprellid populations on the algae were followed. Accompanying the rapid growth of host algae, caprellid populations increased several thousand times during colder months and reached their peak in March. Most of them were lost with decline of host algae in early summer, only a few population survived on perennial Sargassam and red algal undergrowth in summer.

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Kimoto's Cπ has frequently been used as the similarity index of the animal communities, but it had not been always applied to such instances as the analysis of the macrobenthos communities, which are usually composed of many species having various types of life form and large differences of occurrences. The following three indices, therefore, are newly introduced, instead of Cπ.
1) Cπ', the similarity index as a modification of Kimoto's Cπ.
2) Rs, the correlation index between samples, and 3) Rsn, the similarity index of the relationship between samples.
Using these indices, a new statistical method is also proposed for the analysis of the coastal environment. The procedure comprises the spectral decomposition of the matrix [Rsn] and the Fuzzy Cluster Analysis of the results of the spectral decomposition.
The method is verified by artificial data generated with random variables and by actual data of the benthic macrofauna, which were collected from an estuary region off the Inumarugawa river, Oita Prefecture. Consequently, results of the present “Rs” prove to be more effective than those of “Cπ” in both cases, and the analysis of “Rsn” shows satisfactory results on the environments of the research area.
Advantages claimed for this method may be the following points. All collected species are equivalently treated with one another, and many data are simply processed, not setting any artificial standard, such as the dominant or indicator species. Many useful informations about the environments can be drawn from some ecological knowledges peculiar to each species of the cluster species group. From them it is possible to infer some environmental factors of the research area.
As the result, the present method is suitable for the analysis of macrobenthos, and the effect may probably be similar to those of the Principal Component Analysis, which is, in general, difficult to apply to these data, because the sample size is not sufficiently large and also the data generally far depart from the multivariate normal distribution.

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