TAMAI, KYOICHI (Nansei Regional Fisheries Research Laboratory, Kochi).1987. Preliminary study on Sigambra tentaculata (Polychaeta : Pilargidae).Benthos Research (Bull. Jap. Assoc. Benthology), 31 : 1-9.
Morphology and ecology of a small polychaete, Sigambra tentaculata (Treadwell, 1941), were studied in Seto Inland Sea (Suo-nada, Hiuchi-nada and Osaka Bay). The genus Sigambra is characterized by presence of queer recurved hooks on notopodia. Sigambra specimens obtained in Seto Inland Sea were divided into two groups; one is the group in which hooks first occur on the 4th setiger and continue posteriorly, and the other is the group in which they begin from the 7th or 8th setiger. The former agreed with the description of Sigambra tentaculata, and the latter seemed to be S. occelata (Hartmann-Schroder, 1959). Kitamori (1960) formerly described Ancistrosyllis hanaokai (= Sigambra hanaokai, recombined by Pettibone, 1966), the species is distinguished from S. tentaculata only by presence of constriction at the 2nd setiger. According to the result of inspection of many specimens in the present study, however, the feature seemed to be influenced by fixing condition and highly variable by individuals. The feature cannot be reliable as taxonomic character, and S. hanaokai should be regarded as synonym of S. tentaculata.
S. tentaculata have been recorded from many localities of Japan, in the sediment of various texture. The fecundity of this worm was estimated 7000 or more, relatively small egg size (50-60 μm in diameter) suggests pelagic development of larva. Gametogenesis begins in March with rising of mud temperature and stops in September by falling of temperature. The spawning and recruitment occur from May to October. Seasonal change of population structure are also described.

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SEKIGUCHI, HIDEO (Faculty of Fisheries, Mie University) and MASARU TAGAWA (Seikai Regional Fisheries Research Laboratory). 1987. Two Scyllarus species (Crustacea, Decapoda, Scyllaridae) collected from the East China Sea. Benthos Research (Bull. Jap. Assoc. Benthology), 31 : 10-17.
In the course of examining the decapod specimens deposited in the Seikai Regional Fisheries Research Laboratory, which were collected from the whole area of the East China Sea by the R/V Yoko-Maru of the Laboratory, three specimens of Scyllarus bertholdii and five ones of Scyllarus brevicornis were found. Their collection records and description of morphological characters are given.

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TSUTSUMI, HIROAKI and MASAO TANAKA (Amakusa Marine Biological Laboratory, Faculty of Science, Kyushu University). 1987. A new method for measurementof body size and analysis of generation structure of population, using a microcomputer. Benthos Research (Bull. Jap. Assoc. Benthology), 31 : 18-28.
Effective methods for the quantitative study of polychaete population dynamics are noted and a new method using a microcomputer to analyse the generation structure of populations is introduced. For the population study of the animals without age characters such as polychaetes, the resolution of polymodal size-frequency distribution of population is the only way to estimate the generation structure of the population and some population parameters. Over the last decade, we have devised a series of programs for the microcomputer to analyse the generation structure of population from the size-frequency distribution. The body size of worms is measured with a digitizer connected to a computer, and the frequency of each size class is automatically counted. Using a program for a modified graphic method, the polymodal size-frequency distribution of the population is resolved to monomodal ones. The program for the graphic method is explained with an example.

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SATO, MASANORI (Department of Biology, Faculty of Science, Kagoshima University) and MAKOTO TSUCHIYA (Department of Biology, University of the Ryukyus). 1987. Reproductive behavior and salinity favorable for early development in two types of the brackish-water polychaete Neanthes japonica (Izuka). Benthos Research (Bull. Jap. Assoc. Benthology), 31 : 29-42.
Neanthes japonica (a brackish-water polychaete) can be distinguished into two types (the small- and the large-egg types) by the characteristics of egg morphology and developmental pattern (Sato and Tsuchiya, in press). The spawning behavior and the effect of salinity on the early development were studied in the two types. Reproductive swarming was observed in 6 demes of the small-egg type. The swarming worms were carried toward the sea on the ebb after the night high tide, during the spring tides in winter or early spring. It appears that they spawn around the river-mouth, and that they are semelparous. The mature worms of the large-egg type were collected from the sediment in 3 demes in spring, summer and/or autumn. The post-spawners were found within the sediment together with the immature and mature worms, but reproductive swarming was not observed in the case of worms of the large-egg type. The salinity isotonic to the ooplasm of the small-egg type was 27-30, while that of the large-egg type was about 15. The optimal salinity for the early development of the small-egg type was 24-34, while that of the large-egg type was 9-21. These results suggest that the spawning and the early development of the small-egg type occur following the reproductive swarming in water which has a higher salinity, while those of the large-egg type occur in situ in water including a lower-salinity condition.

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SAIGUSA, MASAYUKI (Department of Natural Sciences, College of Liberal Arts and Sciences, Okayama University). 1987. An equipment to monitor the larval release activity in marine invertebrates. Benthos Research (Bull, Jap. Assoc. Benthology), 31 : 47-51.
A simple equipment monitoring the larval and/or gametes release of marine invertebrates in undisturbed condition is described. The activity recording device is based on the principle of detecting changes in transmitting infrared beam in water medium associated the release of larvae or gametes by photo-electric sensor. The recording system consists of a sensor unit (infrared source and receptor : OPE-S100 or E3S-2E4, Omron Co. Ltd.) and a photoelectric-switch unit with amplifier or controller (OPE-VA or S3S-A10, Omron Co. Ltd.).
Ovigerous female animal carrying well developed eggs is kept in a plastic cylindrical case with many pores, and the case is hanging in the glass beaker filled with artificial sea water. Infrared light beam source-receptor unit is set opposite sides of the beaker near the bottom. When larval disperse into the medium in the beaker, and the beam intensity passing through the medium decreases. This triggers a photoelectric switch which is placed outside of the experimental chamber, and the output of the system is monitored by the event recorder (R17-H12T, Fuji Electric Co.Ltd.). For example, experimental set up and results of monitoring of the case of a terrestrial crab, Sesarma haematocheir, are demonstrated.

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