Grain size of substratum was analyzed separately for the surface 1mm and the 10cm depth layers from areas inhabited by Scopimera globosa De Haan and Ilyoplax pusillus (De Haan) in the estuary of Waka River. Difference of grain size between habitats of two species was prominent with respect to amount of fine particles smaller than 0.063mm or 0.125mm in the surface layer: I. pusillus occurred in areas containing larger amount of fine particles than S. globosa. Size frequency distributions of pellet grains were generally similar to those of surface sediments of the habitat of both species, but in I. pusillus the amount of smaller particles in pellets was slightly higher than in the surface sediment. This suggests that there exists sieving process which allows the smaller particles to be concentrated from surface sediment before taking into the mouth in I. pusillus. While intestinal grains were occupied predominantly by fine particles smaller than 0.063mm was higher in I. pusillus than in S. globosa, showing the lower efficiency in sieving the fine particles in the mouthpart in I. pusillus than in S. globosa. Although S. globosa transplanted to I. pusillus-inhabiting area normally performed feeding activities, I. pusillus transplanted to S. globosa-inhabiting area lowered their feeding activities, which may be due to that the content of fine particles in surface sediment was too low for I. pusillus to sieve. Thus it can be considered that amount of particles in surface sediment is significant in substratum preference of both species from the view point of their feeding activities.

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Egg-spawning and browsing behavour of an archiannelid, Saccocirrus uchidai, were studied at a mediolittoral habitat in Oshoro, Hokkaido, north Japan. During the breeding season, May to July, in 1980 and 1981, it was occasionally observed that a number of worms came out from the interstices among coarse Shelly sands, then they spawned eggs or fed over the sediment. Timing, position and abundance for the occurrence of these behavioral phenomena displayed over the sediment were studied together with their under-sediment movement (aggregation and migration). Besides the above, the motions of egg-spawning worms were closely observed in the laboratory condition.

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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Physiological tolerances were studied experimentally in the polychaetous annelids, Capitalla capitata, Parcprionospio pinnata and some organic pollution indicator species. 1) Salinity tolerance: Diopatra bilobata was the most tolerant among four species, C. capirata, Paraprionospio pinnata, Nebalia bipes and D, bilobata. 2) Thermal tolerance: D, bilobata was the most tolerant among above four species, and in the other three species, N. bipes, C. capitata, P. pinnata were in order from high to low in tolerance. 3) COD tolerance: The range of COD concentration in chich survivorship of the worms examined exceeded 50% for C. capitata was 27.5 to 57.0 ppm and as for D, bilobata was from 12.0 to 22.0 ppm. 4) Tolerance to the combination with temperature and salinity, temperature and COD concentration: The more salinity decreased, temperature increased and COD concentration decreased, the more survivorship of C. capitata decreased. 5) Tolerance to low oxygen tension: Lowest point of dissolved oxygen concentration of independent zone of oxygen consumption was 2.1 ml/l in C. capitata and 2.4 ml/l in D. bixobata. C, capitata was more tolerant than D, bilobata in. low oxygen tension.

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In Ago Bay along the Pacific coasts of central Japan, a great number of the nebaliid specimens were found to inhabit the half-decayed cavity, filled with the black-coloured deteriorated water, of the old poriferans Heliclona permollis. The nebaliid specimens obtained were described on the basis of young and mature specimens, with the result that the specimens were identified to be Nebalia bipes japanensis which accorded with the description of Jancowski.

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