寒武纪的“蚯蚓”——鳃曳动物*

鳃曳动物在寒武纪曾经辉煌一时，但因躯体构型以及生活方式等诸多因素限制，其各大支系随后相继绝灭，唯有鳃曳形目一息尚存至今。研究表明鳃曳形目自寒武纪以来形态未发生较大变化，无论在宏观还是分子水平都属于活化石，这种进化保守性以及新近发现的寒武纪胚胎化石对于了解动物的变态发育起源至关重要。

Cambrian Earthworms:Priapulans

Most of their clades of the Priapulan terminated their evolutionary history immediately after their rapid diversification in the Early Cambrian, probably due to the constriction of many factors such as body plan, life style etc. However, Cambrian priapuomorphs convincingly resemble their recent descendents, supporting that this clade remain stagnant in morphology, and really being a kind of living fossils either in anatomical or molecular level. This evolutionary feature, together with recent findings of priapulans-like fossil embryos, is rather critical to investigate into the origin of the metamorphosis of metazoans.