The benthic snailfish Liparis tanakai (GILBERT et BURKE) is widely known from the East China Sea, Yellow Sea, Gulf of Po-Hai, Japan Sea, and the Pacific coasts of northern Japan, although its occurrence in the Seto Inland Sea located in southwestern Japan and its adjacent waters has been fragmentarily reported since 1970. The occurrence of the species in the Seto Inland Sea was confirmed by comparing the specimens with those from other localities. Many findings of the species around the Kui Peninsula, no capture record from Tosa Bay, the presence of a large cold water mass in the Enshu-nada Sea, and a coastal front formed during winter in the Kui Channel suggest that more snailfishes invaded the Seto Inland Sea through the Kui Channel than the Kan-mon Channel during winter. In addition, an extreme cold wave seems to promote the invasion.

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The present study describes the spatial and temporal distributions of the planktonic and benthic phases of bivalves in a tidal estuary of the Kiso River, and gives insights into larval retention within the estuary. Patches of planktonic larvae of Corbicula japonica, absolutely dominant among the sampled larvae in July, were found along two troughs in the estuary, and were thought to move back and forth together with the saline water which intruded into the estuary during flooding and ceased from there during the ebb tide. These larvae were detected mainly in the lower, saline water strata. Shortly after the settling of planktonic larvae onto the bottom sediment, juveniles with shell length of less than 0.5 mm were scattered widely within the whole surveyed area. Juveniles of Nuttalia olivacea were not found in August, but youngs of this species with shell length of 1.0-1.5 mm were found scattered widely within the downstream sector of the surveyed area and those with shell length of more than 2 mm were densely distributed at the stations along both of two troughs.

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Histological examination of the great tellin Megangulus venulosus revealed the developmental process of germ cells which is divided into four stages, as follows : in female, they are oogonia, yolkless oocytes, yolk granule oocytes, and mature oocytes ; in male, they are spermatogonia, spermatocytes, spermatids, and spermatozoa. An annual breeding cycle is composed of recovery period (March-May), growing period (May-August), mature period (September), spawning period (October), and spent period (November-February). Growth curve in shell length estimated by external growth rings shows a lower growth rate than previously reported tellinid bivalves. Shell length at the first sexual maturity defined as the length class at which 50 % of the clams mature is 50-55 mm for male and 65-70 mm for female. Based on the number of external growth rings, these sizes correspond to the age of six for male and eight for female. All the clams become mature when they grow larger than 75 mm in shell length. It takes about 10 years for the entire population of M. venulosus to become sexually mature.

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The mating behavior patterns of brachyuran crabs are reviewed from a viewpoint of sexual differences in mating strategy. The ways males find mates are put into two categories : males may anticipate the occurrence of receptive females temporally or spatially from the change in the environmental conditions, or males may recognize the receptivity of females, based on the informa. tion the females give. Precopulatory mate guarding has been recorded mainly in species in which mating is confined to a short period of the female's reproductive cycle and males can foretell when females will become receptive. Postocopulatory guarding and sperm plug have been recorded in various species, and are considered to be associated with male.male competition over mates. For some species, females may choose mates with good resources or with other favorable traits.

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