The rapid appearance of skeletons in various marine invertebrates in the beginning of the Cambrian produced the sudden explosive increase of the animal fossils. This dramatic evolutionary event was not performed by the explosive diversification of marine life but simply by the physiological changes of the organisms in increasing oxygen pressure in the earth's atmosphere. According to the recent physiological studies, various marine animals can survive in low dissolved oxygen conditions of rather long period with an anaerobic metabolism, suggesting the respiratory mechanisms of the primitive forms in the Precambrian. The anaerobic metabolic activities imposed some physiological restrictions on the animals through the acidic end-products (eg, inhibition of skeleton formation, small body size, and low metabolic efficiency etc.). The skeleton formation in the Cambrian life was initiated by the advent of aerobic metabolism, which indicated the release from the physiological restrictions by the anaerobic metabolism.

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As a fundamental study on paleoenvironmental reconstructions based on fossil diatom assemblages, information on processes of their formation is indespensible, because well preserved celles of diatom, composed of silica, make a mixture both autochthonous and allochthonous member in an assemblage. In the present paper such fundamental problems were examined. As a result, it turned out that dead diatom cells were widely transported in a tidal zone, especially to make mixed assemblages in mud flats, residual ones in sand flats and autochthonous community in salt ponds. In-flow of allochthonous cells made the preservation ratio of a assemblage lewered and the structure changed depending on the addition of them. And a model on formations of fossil assemblages in some environments was introduced. On the basis of those fundamental studies, fossil diatom assemblages formed at the Jomon transgression in Holocene were analyzed. As a result, such phenomena as reworked cells from older sediments, transportation of allochthonous cells to the offshore from the coastal area, concentration of allochthonous cells in the tidal area, were observed in fossil assemblages.

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The seasonal samplings of diatoms were done in the three brackish lakes (Lake Namako-ike, Lake Kai-ike and Lake Kazaki-ike) with different salinity in Kamikoshiki Island. The characteristic in diatom distribution of those brackish lakes are, as follows.(1) The diatom distribution is mainly affected by the change of the salinity of the surface lake water (0.5 m depth). But the tolerance of salinity change is very different between diatom species.(2) The number of planktonic diatom cells in the lake water is very variable seaseenally. But the number of perifytic diation cells at the lake shore hardly change seasonally.(3) The distribution of perifytic diatom at the lake shore is affected by the small change of water depth and the characteristic in each attached substrata.

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I analyzed the vertical distribution of benthic foraminifera within sediments. Samples are collected from the Pacific, facing to the Central Japan. I also cultured sublittoral to middle bathyal benthic foraminifera in laboratory for ecological observations. Benthic foraminifera are vertically stratified within sediments. Both epi-and infaunal life habits are recognized among benthic foraminiferal species. Foraminifera belonging to the same life habits have similar shell characters, and have similar colours of cytoplasm. Surface dwelling foraminifera have low trochospiral or planispiral chamber arrangements, and also have thick and strong chamber walls. Foraminifera which are living within sediments have high trochospiral tests. They have thin, transparent chamber walls. Cytoplasm through chamber wall shows black in colour. It is probable that these species have symbionts in their cytoplasm.

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Trace fossils, Chondrites (small-and large-forms), Zoophycos and spatangoid echinoid burrows (A-type and Subphyllochorda), occur abundantly in the turbidite sequences deposited under the bathyal conditions in Boso Peninsula, central Japan. Tiered structure made by benthic animals with different burrowing depth can be recognized within a mudstone unit. The following succession of burrows is recognized from shallowest to deepest : Subphyllochorda (tier-I), echinoid burrow (type-A) and Zoophycos (early-stage) (tier- II), Chondrites (large-from) (tier-III), and Chondrites (small-form) and Zoophycos (tier-IV). Apart from the case of raphid sedimentation of volcanic ash, Subphyllochorda produced on the sea-floor seems to have destroyed by turbidity currents and locomotion of epibenthos, and rarely preserved as fossils. The early-stage of Zoophycos and spatangoid echinoid burrow (type-A) frequently observable at the upper portion of mudstone unit have been destructed post-mortemly by echinoid locomotion and turbidity currents. Chondrites and the middle-to latestages of Zoophycos, which occupies the lowest tiers, are mostly preserved perfectly within sediments. Fossilization of the trace fossils in turbidite sequence seems to be strongly dependent on the difference in burrowing depth of trace producers and turbidite sedimentation system.

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Experiments in the laboratory and in the field have shown that growth lines and growth bands are produced during the emersion and immersion periods respectivelly, and that the growth band width is correlated with the period of submergence. These results can be applied to the analysis of detailed paleoenvironment of Intertidal barnacles.

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Sixteen spatangoid species examined are grouped into three types on the basis of their test shape and habitat. The first type having flat shape burrows shallowly in sand, the second type having globular shape burrows deeply in sand, and the third type having wedge shape burrows in mud. The test shape bears a basic relation to resistance of sediment through which they move. Different burrowing mechanisms seen among them are derived from the difference in test shape and resultant function of spines. Test shape of each type and the specific burrowing mechanism fit with respective habitat conditions.

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A set of related species living in different habitats is suitable to evaluate various adaptive characters to habitats, particularly in a such set where plural genera are recognized. Functional morphology of ostracods, especially their carapace shape, is thoroughly studied here through observation of the different mode of behavior between phytal and bottom-dwelling species of Loxoconcha and some other genera in seagrass beds. The phytal species living on smooth leaf-surface of seagrasses such as Zostera have vertically compressed carapaces with blade-shaped ventral part. On the contrary, the bottom-dwelling species in Zostera beds are cubic with flat ventral plane or streamlined in the carepace shape. The characteristics of the phytal is directly related to the style of copulation which is adopted (ventral-to-lateral position) to do not slip down to the bottom during copulation. The bottom-dwelling species copulate in ventral-to-ventral position and their shapes of the ventral part seem to be controlled by not the copulation style but the mode of behavior whether more epibenthonic or inbenthonic. Functional characters of soft parts, such as sexual organ and the tip of the appendages, are also documented, and the significance of analyses of “breeding”, in general, is emphasized to understand Ostracoda.

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The male Copulatory organs, which are important for the Recent ostracode taxonomy, were compared in the ten Cythere species and the relationship between the copulatory organ and the geographic distribution was examined. For nine pairs of species whose geographic distributions overlap with each other, copulatory organs are morphologically different. Conversely, the pairs of species with similar copulatory organs show either of the following characteristics ; 1) their distribution-al areas completely isolated, or 2) their distribution-al areas are very close or more or less overlap each other, but their breeding seasons or their habitats are different. In the case of Cythere, consequently, the diversification of copulatory organ does not seem to reflect taxonomic distance between species. On the other hand, the number and the distribution of normal pore canals on the carapace were traced from the early stages when the distribution-al patterns are identical among all the Cythere species, to the adults which have their own patterns. As a result, the phylogenetic relationship of Cythere species was reconstructed with semi-quantitative estimation of the phylogenetic distance.

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