多毛纲环节动物软背鳞虫的电镜观察与描述及其与Wiwaxia骨片微结构的比较

SEM OBSERVATION OF THE POLYCHAETE LEPIDONOTUS HELOTYPUS GRUBE,1877 AND ITS COMPARISON WITH THE CAMBRIAN ANIMAL FOSSIL WIWAXIA

通过对现生环节动物门(Annelida)多毛纲(Polychaeta)叶须虫目(Phyllodocidae)鳞沙蚕亚目动物(Aph-roditiformia)软背鳞虫(Lepidonotus helotypus Grube,1877)的鳞片、刚毛等疣足附属物的超微结构观察及其与Wiwaxia骨片的比较研究,探讨Wiwaxia的系统分类位置。研究结果表明,软背鳞虫的刚毛与Wiwaxia骨片具有以下相似性:1)两者表面均具有浅纵纹;2)均向身体背中线方向倾斜或弯曲;3)着生方式均以刚毛囊或类似根状基的结构插入软组织。此外,文中首次对鳞片上的锥形突起与Wiwaxia骨片的相似性进行比较和探讨。结果显示,Wiwaxia骨片与鳞沙蚕刚毛具有一定相似性,但在形态上仍存在显著差异(如二者的排列方式不同,Wiwaxia骨片上不存在鳞沙蚕刚毛的覆瓦状结构等)。

The Cambrian problematic animal fossil Wiwaxia corrugata has been interpreted as an annelid,a mollusk,or a stem group of lophotrochozoan,mostly based on the proposed similarities in microstructures.This paper presents electron microscopic observations of the setae and scales of Lepidonotus helotypus Grube,1877,an aphroditiform polychaete.This taxon was chosen for microstructure study because of its scale-like structures that may be similar to the sclerites of wiwaxiids and other Cambrian animals.One specimen of Lepidonotus helotypus has been studied in detail using an ESEM.The results reveal that there are some similarities between Lepidonotus helotypus setae and wiwaxiid sclerites:1) both have shallow elongate striations on the surface;2) both are bent toward the dorsal midline of the animal;3) both are inserted to the animal body through an invaginated pocket.The scales of Lepidonotus helotypus are covered with cone-shaped chitinous tubercles(～60 μm in diameter) and small papillae(～8 μm in diameter) which also share some microstructural similarities with wiwaxiid sclerites.These observations provide some support to the microstructural similarity between certain annelids and wiwaxiids,but the significant morphological differences should not be overlooked(e.g.,the arrangement of sclerites in wiwaxiids and setae in Lepidonotus is different;wiwaxiid sclerites do not have serrate ornamentations that occur in Lepidonotus setae;the size of wiwaxiid sclerites and Lepidonotus chitonous tubercles and papillae on the scales are different).