Halwaxiids系统进化研究进展

PROGRESS AND PROSPECTS IN PHYLOGENETIC RESEARCH ON HALWAXIIDS

Halwaxiids是一类体表覆有骨质鳞片的寒武纪后生动物,它包含了在早期后生动物进化中占据关键位置的两个化石动物类群Halkieriids和Wiwaxids。但自1995年以来包含Halkieria和Wiwaxia在内的Halwaxiids进化枝在不断被修正,而近年来,随着新化石和新证据的出现,围绕Halkieria和Wiwaxia的分类归属展开了更激烈的争论。争论焦点集中在以下问题:Halkieria和Wiwaxia的亲缘关系到底如何?Halkieria究竟属于冠轮动物的基群,还是可直接归为软体动物或环节动物?Wiwaxia是软体动物还是环节动物的基群?这些问题的解决将为确定Halwaxiids的系统分类地位提供重要依据,将使描述环节动物与软体动物在分化初期的身体构造趋势成为可能,也将为软体动物、环节动物和腕足动物的起源与分化关系提供重要线索和基本资料。

The Halwaxiida is a clade proposed by Conway Morris and Caron（2007） consisting of the sclerite-bearing Cambrian metazoans Halkieria and Wiwaxia and related taxa.Phylogenetic affinities of halwaxiids however have been contentious. Recent description of newly discovered fossils sheds fresh light on halwaxiids but also raises more questions.The key unresolved questions are： Do halkieriids and wiwaxiids actually belong together to a monophyletic group？ Alternatively,are halkieriids stem group lophotrochozoans,crown group mollusks or crown group annelids？ Or are wiwaxiids stem group mollusks or stem group annelids？ There is a need for more fossil materials,and more rigorous cladistic analysis,which may lead to a better understanding of relevant homologies,as well as answers to the questions mentioned above.The answers will help clarify the phylogeny of halwaxiids,eventually unveiling the early evolutionary history of annelids,mollusks,and other lophotrochozoans.