贵州瓮安埃迪卡拉纪陡山沱组磷块岩中具螺旋孔的微体化石

SPHEROIDAL FOSSILS WITH HELICALLY DISTRIBUTED PORES FROM THE EDIACARAN DOUSHANTUO PHOSPHORITES OF WENG'AN,GUIZHOU

文中对贵州瓮安埃迪卡拉纪陡山沱组磷块岩中一类具螺旋孔的微体球形化石进行形态功能学分析,并与原生动物肉足虫纲的类群进行比较。结果显示它们是一个独立的分类单元,属于单细胞原生动物,并命名为瓮安旋孔虫(新属、新种)(Helico foramina wenganica gen.et sp.nov.),与已报道的胚胎化石很可能没有亲缘关系。虽然这类化石生物很可能属于原生动物肉足虫纲,但还不能归入其已知的目,也许属于新的目一级分类单元。螺旋孔是伪足伸出的孔洞,它们起到了取食、运动和排泄的作用。该类化石生物的个体生长是通过阶段性地脱去外部壳体、再由原生质体分泌出新壳体的方式来实现的。

Helically coiled small spheroidal fossils like those described here were first discovered from the Ediacaran Doushantuo Formation of southern China by Xiao et al. , （2007） - who considered them to be post blastula embryos related to Megasphaera ornata. They also discussed possible relationship with Sinocyclocyclicus guizhouensis. The present study shows however that these fossils are very different in structure and hence we reach different conclusions about their relationships. A new taxon, Helicoforamina wenganica gen. et sp. nov. is established accordingly. Although Helicoforarnina wenganica gen. et sp. nov. and Megasphaera ornata are indeed similar to each other in size, and both are ornamented with tubercles on their external walls, H. wenganica differs in being helically punctuate, having a helix of holes on the external wall that go through it and penetrate into the otherwise more or less smooth exterior of the inner wall. Megasphaera （and Parapandorina） also differ in having the 1 to 2n divided cells that were assumed to be embryos at different stages by Xiao et al. （1998）. Consequently Megasphaera （ and Tianzhushania） have been interpreted as animal embryos preserved inside diapause egg cysts （Yin et al. , 2007, 2008; Yuan et al. , 2009）. Helicoforamina wenganica gen. et sp. nov. has characters very similar to those of the modern protozoan group Sarcodina. As such it differs from the embryo fossils just discussed and should be referred to an independent taxon. The clockwise helically arranged holes may represent openings for pseudopods, and may have functioned in locomo- tion, feeding, and drainage. Growth in size would be facilitated by periodic exudation of the protoplast.