Monthly samples of the introduced spider crab have been taken over three years in the innermost area of Tokyo Bay. Adult spider crabs were killed by oxygen deficiency in late summer, and recruitment occurred in late fall. Young crabs grew through winter, and reached maturity by early spring ; females began carrying eggs soon after maturation. From spring to early summer, the crab population consisted principally of matured males and females (>9 mm in carapace width) ; larvae were produced throughout this period. Young crabs (<5 mm in carapace width) produced in these seasons were found during late spring to early summer ; most, however, disappered before maturing along with adults when the summer oxygen deficiency was established. Seasonal changes in the population structure showed almost the same pattern in three years. This indicates that larvae produced in the innermost region of the bay do not contribute to the recruitment, and that the crab population in this region is maintained by settlement of larvae during late fall which may be produced from individuals surviving in the oxygen rich environment in mixed region of the bay.

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Interspecific interactions between two species of grass shrimps, Latreutes acicularis and Heptacarpus geniculatus living on Zostera marina leaves, were studied in aquaria. These species compete for space on Zostera leaves as a refuge. In encountering between individuals of two species, crawling retreat or jumping avoidance was observed frequently. Latreutes acicularis was inferior species at the encountering than H, geniculatus. Even without refuges, a predatory fish, Hypodytes rubripinnis, prefers L. acicularis as a food. However, when housed with the predator, encountering among individuals of shrimps reduced significantly by inactive behaviors of both species. The competitive interactions for refuges between two species of shrimps, are remarkably depressed under existence of predators, and thus coexistence of these species could be sustained.

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Polyester resin is very useful for studying the burrows of benthic animals. A simple method of making resin casts of burrows, both tidal and subtidal, is introduced here. A transparent wide tube made from a plastic, soft drink, bottle is driven into the mud surface surrounding a burrow opening. A clear polyester resin containing accelerator and wax is mixed with catalyzer at a 0.5-1.0 %(v/v) concentration in a polyethylene bag in a pail, air is removed from the bag and its opening is fastened tightly. Then the resin is poured from a cut corner of the bag into the plastic tube over the burrow opening until the burrow is full. After hardening the cast can be dug out from the bottom and both adhesive bonding of broken casts and trimming of extraneous parts can be carried out.

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In identification of juvenile bivalves immediately after settling onto the sea bottom, it is necessary to examine the characters of their hinge apparatus. Several methods hitherto used require several hours to prepare the specimens for observation on morphological features of the hinge. A simple method to examine the features of the hinge is here proposed : Stick a piece of double-sided sticking vinyl tape on a slide glass, cut a triangular slit on the tape, put the specimen onto the cut slit by using a sucker tube, and place the specimen in a correct upright position with a needle with a minute fragment of the tape on the tip.

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