MORPHOLOGY AND BIOLOGY OF POLYSACCUS-JAPONICUS (CRUSTACEA, RHIZOCEPHALA, AKENTROGONIDA, POLYSACCIDAE, FAM N), A PARASITE OF THE GHOST-SHRIMP CALLIANASSA-JAPONICA

The morphology and biology of Polysaccus japonicus Hoeg & Lutzen, 1993 is described. Nearly all infected hosts are adults, the females of wh ich become castrated. Each bears 4-50 (female) externae on the undersi de of the abdomen. The externae are interconnected via a root system w ithin the host's perineural blood sinus. The externae pass through thr ee moults. Cypris larvae inject spermatogonia into the immature extern a's mantle cavity, which is where spermiogenesis occurs later. Multipl ication of the male cells is probably supported by secretion from pair ed mantle cavity glands, presumably homologous to the receptacles of k entrogonid rhizocephalans. Late during the 2nd intermoult the visceral mass ruptures to release the ova into the mantle cavity where they be come fertilized. The third moult results in opening of the mantle aper ture which initiates a period of vigorous peristalsis of the muscular mantle. Following emission of the cypris larvae the externae perish le aving distinct scars. The root system always contains buds of various sizes and stage of development. When the scarred host moults, the most advanced buds emerge to give rise to a new generation of externae. Th is is thought to be repeated for the rest of the host's life. The ante nnule of the cyprid has a relatively very long and slender 3rd segment , a unique construction among Akentrogonida. Because of this and the p resence of special mantle cavity glands, a new family, Polysaccidae, i s erected, which in some characters is intermediate between the Kentro gonidit and the Akentrogonida.