Preliminary study on Sigambra tentaculata (Polychaeta : Plilargidae)

Abstract

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.