Echinoderm Phylogeny Including Xyloplax, a Progenetic Asteroid
Echinoderm Phylogeny Including Xyloplax, a Progenetic Asteroid
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DOI：
10.1093/sysbio/syr044
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发表时间：
2011-07-01
影响因子：
6.5
通讯作者：
Daly, Marymegan
中科院分区：
文献类型：
--
作者：
Janies, Daniel A.;Voight, Janet R.;Daly, Marymegan
重建棘皮动物门现存的五个纲的系统发育已被证明是困难的。棘皮动物之间的高层次分类关系的结果是敏感的分析参数和方法的选择。此外，20世纪80年代，根据巴哈马和新西兰深海中的一种神秘的圆盘状棘皮动物Xyloplax提出了推定的第六类动物，这进一步使问题变得复杂。虽然显然是棘皮动物，但在已知的类群中没有明显的亲缘关系。使用分子序列和发育数据，从最近收集的Xyloplax成人和胚胎，我们表明，而不是代表一个古老的独特的血统所暗示的地位作为一个类，Xyloplax只是一个海星，是密切相关的小行星家庭Pterplusdae。许多翼龙科的成员和所有的木虱栖息在深海或极地海洋和育雏。孵卵的翼龙和木虱把它们的幼仔关在专门的成年室里，直到幼仔达到高级的少年阶段，之后它们作为自由生活的个体被释放。我们推测，独特的形态学的Xyloplax进化通过progenesis-截断体细胞生长在少年身体计划，但与性腺生长到成熟。虽然现存棘皮动物的整体发育仍然对分析方法的选择敏感，但将Xyloplax作为翼龙类小行星的姐妹是明确的。在此基础上，我们认为，建议的类和亚类地位的Xyloplax应予以抑制。
Reconstruction of the phylogeny of the five extant classes of the phylum Echinodermata has proven difficult. Results concerning higher-level taxonomic relationships among echinoderms are sensitive to the choice of analytical parameters and methods. Moreover, the proposal of a putative sixth class based on a small enigmatic disc-shaped echinoderm, Xyloplax, from the deep seas of the Bahamas and New Zealand in the 1980s further complicated the problem. Although clearly an echinoderm, Xyloplax did not have clear affinity among known groups. Using molecular sequence and developmental data from recently collected Xyloplax adults and embryos, we show that rather than representing an ancient distinct lineage as implied by its status as a class, Xyloplax is simply a starfish that is closely related to the asteroid family Pterasteridae. Many members of the Pterasteridae and all Xyloplax inhabit deep or polar seas and brood young. Brooding pterasterids and Xyloplax hold their young in specialized adult chambers until the young reach an advanced juvenile stage after which they are released as free-living individuals. We hypothesize that the unique morphology of Xyloplax evolved via progenesis-the truncation of somatic growth at a juvenile body plan but with gonadal growth to maturity. Although the overall phylogeny of extant echinoderms remains sensitive to the choice of analytical methods, the placement of Xyloplax as sister to pterasterid asteroids is unequivocal. Based on this, we argue that the proposed class and infraclass status of Xyloplax should be suppressed.