Taxonomy and life history of the scale worm Hesperonoe hwanghaiensis (Polychaeta: Polynoidae), newly recorded in Japan, with special reference to commensalism to a burrowing shrimp, Upogebia major

Abstract

A unique scale worm Hesperonoe hwanghaiensis Uschakov and Wu, 1959 (Polychaeta: Polynoidae) was collected from tidal flats in Japan and is described here taxonomically as the second record of this species since its original description from Chinese specimens. Some morphological features of our specimens differed slightly from the original description of this species. Marked differences in growth pattern, morphology of elytra and microhabitat were demonstrated between juveniles (1.8 mm or less in body width) and adults (1.9 mm or more). We estimated the outline of the life history of the scale worm by sampling it in various seasons. The scale worm was commensal with the burrowing shrimp Upogebia major. Juveniles of the scale worm were commonly attached to the ventral or lateral surface of the thorax or abdomen of the host throughout May to September in Isahaya Bay in the Ariake Sea, Kyushu. In July 1998, 89% of the host shrimps were infested by the scale worm. Several juveniles (maximum: 7) of the scale worm often aggregated on a host body, with no adults found on the hosts. The adults were collected from sediment samples. These results suggest that the juveniles mainly live on the surface of the host body and that they later detach themselves from the host body and live freely on the inner surface of the burrow of the host.