鳋属(寄生桡足类)一新种

A NEW PARASITIC COPEPOD OF THE GENUS ERGASILUS

1982年4月20日广西水产研究所周解等同志在桂林住岩的溶洞水中,用浮游生物网采集水样,采得了鳋属(Ergasilus)的标本5个(2♂♂、3♀♀),其中二个雌体携有卵囊,经仔细观察研究,认为是鳋属的一个新种,现报道如下。 模式标本保存于中国科学院昆明动物研究所。

Ergasilus longicaudatus,sp.nov.Holotype:Zhuyan,Quilin,Guangxi,Ⅳ.20.1982 Auotype:Paratype:21 from the same locality as holotype.Measurements(mm):Female total length 0.95-0.99;head 0.33-0.34,its width 0.32-0.34,1st thoracic segment 0.14-0.15,its width 0.25-0.30;genital segment 0.093-0.11,its width 0.12;caudal rami 0.10-0.11;egg sac 0.22-0.44.Male total length 0.83-0.88;head 0.25-0.28,its width 0.24-0.28;1st thoracic segment 0.087-0.094,its width 0.22-0.25;genital segment 0.094,its width 0.080-0.086;caudal rami 0.12-0.13.Diagnosis:This new species resembles E.chautauquaensis in general ap-pearence,but the former can be easily distinguished from the later by the following characters.1.In the new species,there are a pair of large and sub-rounded processess on dorso-lateral sides of the 2nd thoracic tergite.These processes are completely lacking in E.chantauquaensis.2.The 1st endopod is 3-segmented instead of 2-segmented in E.chautauquaensis.3.The 4th exopod is 3-segmented instead of 2-segmented in E.chautauquaensis.4.In the new species,the pair of long caudal setae are shorter than that of E.chautauquaensis.5.The arrangements of spines and setae on legs are different.6.The eggs are arranged in single longitudinal row in egg sac.This is unique and particular to all other congeners.Habitat:The specimens were collected at Zhuyan,near the city of Quilin,Guangxi.The hill where the cavern locates is surrounded by ponds and fields.The opening of the cavern is situated about 10 meters above the ground surface.The new species is living in a dark environment with an area of 20 m2 and a depth of 0.5m,supplied by alkaline subterranean water.Discussion:So far as we know,with the exception of E.chautauquaensis,ergasilids are represented in the plankton only as nauplii,copepodids,males and non-ovigerous females,whereas the adult females are ectoparasitic on fish.Ovigerous females of E.longicaudatus are observed in plankton for the first time in China.It is important to point out that some features of the new species usually appear also in free-living cyclopoids and seem to be primitive ones,such as the cephalon not fused with 1st throcic segment,the 4th leg with a 3-segmented exopod and caudal rami being very long.Considering these facts,the authors assume that the new species may undergo a free rather than parasitic way of life.