Xyloplax is an asteroid
Xyloplax is an asteroid
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Xyloplax 是一颗小行星
DOI：
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发表时间：
1998
期刊：
影响因子：
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通讯作者：
D. Janies
中科院分区：
文献类型：
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作者：
D. Janies
同心圆类动物是最近在新西兰和巴哈马群岛深海的沉没木材上发现的小型圆盘状棘皮动物。它们的水血管系统是圆形的，而不是棘皮动物的特征--五向的。由于这种非凡的身体结构，棘皮动物门的一个新纲（现存的第六个纲），同心环总科被建立起来，以容纳两个种类的木甲属。这一分类仍然存在争议，因为它意味着木虫是一个古老的类群，是所有小行星和蛇类的姐妹类群。我们测试了有效性的'类Concentricycloidea'的核苷酸序列和形态学的分支分析，从最棘皮动物的订单范例。在最一致的总证据树中，木甲是嵌套在一个单系的星总科中。因此，等级的阶级是一个不适当的代表性的进化历史的同心摆线，应予以抑制。此外，这些结果表明，在小行星多样化的后期，天体组织的基本特征不稳定。
Concentricycloids are small disk-shaped echinoderms recently discovered on sunken wood from the abyssal seas off New Zealand and the Bahamas. Their water-vascular system is circular rather than pentaradial as is characteristic of echinoderms. As a result of this remarkable body plan, a new class (the sixth extant) of the Phylum Echinodermata, Concentricycloidea, was erected to accommodate two species of genus Xyloplax. This classification remains controversial because it implies that Xyloplax is an ancient group that is a sister taxon to all asteroids and ophiuroids. We tested the validity of the 'class Concentricycloidea' with cladistic analyses of nucleotide sequences and morphology from exemplars of most echinoderm orders. Xyloplax is nested within a monophyletic Asteroidea in the most congruent total evidence tree. Thus the rank of class is an inappropriate representation of the evolutionary history of the concentricycloids and should be suppressed. Moreover, these results suggest that fundamental features of body organization were labile late in the diversification of the asteroids.