REDESCRIPTION OF ADULTS AND DESCRIPTION OF DEVELOPMENTAL STAGES OF TREBIUS SHIINOINAGASAWA, TANAKA & BENZ, 1998 (COPEPODA, SIPHONOSTOMATOIDA, TREBIIDAE) FROM THE JAPANESE ANGELSHARK, SQUATINA JAPONICA BLEEKER, 1858

摘要

A redescription of Trebius shiinoi Nagasawa, Tanaka & Benz, 1998 and descriptions of its developmental stages, nauplius I and II, copepodid I, II (female), III (female), IV (female) and V (male) are presented based on specimens obtained from the Japanese angelshark, Squatina japonica Bleeker, 1858, captured at Seto and Kushimoto, Wakayama Prefecture, Japan, in 1971-1972. The family is the second representative of the Siphonostomatoida known to have nauplii with spatulate balancers, next to Caligidae.However, T. shiinoi also differs significantly from caligids in lacking a chalimus phase in its life cycle. The postnaupliar development of the species involves a single morphological leap, which takes place through a moult from copepodid II to III, andthen development proceeds linearly up to the adult. The majority of the copepodids I found appear to have already been grasped by an adult male each (precopulatory mate guarding). Copepodid II exhibits sexual activity by the possession of a spermatophore receptacle in the female. Copepodids after copepodid III are caligiform, having marginal membranes on the cephalothrax, as in the adult. Copulation takes place at least in copepodid III and/or IV, and the spermatozoa discharged are stored in the genital antra to later fertilize the ova in the adult. Judging from the fact that in the adult female a spermatophore receptacle is absent, it is deducible that no copulation is taking place in the adult stage. This reproductive process is unique in the Copepoda.