ブリ寄生単生類<i>Heteraxine heterocerca</i>の発達およびその不相称性と寄生部位との関係

Abstract

Redescription is given of the development of a monogenean, Heteraxine heterocerca, based on about 70 immature specimens from the gills of Seriola quinqueradiata and 26 oncomiracidia hatched from naturally laid eggs. The egg is ovoid with a long filament basally. The structure of the oncomiracidium and the post-oncomiracidial development up to the stage of 5 pairs of clamps are quite similar to those of microcotylids, suggesting a close relationship of H. heterocerca to the family Microcotylidae. Asymmetry is first recognized at the stage of 5 or 6 pairs of clamps. The larval anchors and the marginal hooks I come off together with the surrounding tissue at the stage of about 10 clamps on the long side of the opisthohaptor. The chitinous structures existing on the oncomiracidium are replaced by clamps except the domus of the marginal hooks III to V. The number and size of clamps on one side of the opisthohaptor increase much more than those on the other, reaching the same degree as in adults before attaining sexual marurity. An examination of 289 asymmetrical specimens reveals that, like other asymmetrical monogeneans, the asymmetry of H. heterocerca strictly depends on the water flowing on the gill filament to which the parasite attaches itself.