双峰无齿蚌Anodonta bigibba(Heude)非寄生变态发育的研究

STUDIES ON THE DEVELOPMENT OF METAMORPHOSIS WITHOUT PARASITISM IN ANODONTA BIGIBBA (HEUDE)

1993年4、5月份观察到双峰无齿蚌Anodonta bigibba(Heude)母体排出的不是钩介幼虫,而是幼蚌。幼蚌壳中具一呈似三角形、较厚的钩介幼虫外壳,其腹缘顶端具壳钩。幼蚌在原钩介幼虫壳缘生长了1—4环新壳,而且具育带纤毛的足、前后闭壳肌、管状鳃原基和肛门孔等。幼蚌在室内试养存活了39天,显示已具独立生活能力。研究表明,该蚌钩介幼虫在母体育儿囊中已经历并完成变态,发育成幼蚌。这是我国首次发现的一种非寄生变态发育的珠蚌类,对于研究我国珠蚌类的进化及与世界淡水贝类的亲缘关系有着重要价值。此外,鉴于双峰无齿蚌与背角无齿蚌Anodonta woodiana(Lea)的成体壳形和发育生活史的不同,应恢复Heude建立的双峰无齿蚌的种名。

Young mussels instead of glochidia were observed to be discharged by gravid individuals of Anodonta bigibba(Heude) in April and May of 1993. Among the shells of the young mussel, a stout, triangular shell of glochidium and its hooks at the far end of the ventral margin were in evidence. Loops of newly grown shell were found to be around the glochidial shell, and a ciliated foot, anterior and posterior abductors, gill rudiments, and anus could also be recognized. The young mussels were kept alive in laboratory for 39 days, indicating that they had the ability to live independantly. It is made clear by the study that the glochidia of this mussel species has undergone the metamorphosis inside the maternal marsupia. It is the first time to find in China a naiad species metamorphosing without parasitism, a significant fact for studying the evolution of Chinese unionid and its phylogenetic relationships with world freshwater mussels. Furthermore, in view of the differences of adult shell and life history between Anodonta bigibba (Heude) and Anodonta woodiana (Lea), the name of A. bigibba given by Heude should be recovered.