The Nemertodermatida are basal bilaterians and not members of the Platyhelminthes
The Nemertodermatida are basal bilaterians and not members of the Platyhelminthes
复制标题
DOI：
10.1046/j.1463-6409.2002.00090.x
复制
发表时间：
2002-04-01
影响因子：
2.5
通讯作者：
Riutort, M
中科院分区：
文献类型：
--
作者：
Jondelius, U;Ruiz-Trillo, I;Riutort, M
最近关于后生动物系统发育的假说已经确认了两国动物的三个主要支系：后口纲、蜕皮纲和细毛纲。包括扁形蠕虫在内的后生动物--包括扁形蠕虫--长期以来一直被认为是基本的双边动物，许多作者将其称为这些分支中的位置。然而，最近一项基于核糖体DNA的研究将扁虫群体Acoela列为所有其他现存的双边血统的姐妹群体。出乎意料的是，线虫，通常被认为是Acoela的姐妹群，共同形成了Acoelama，与Acoela分开，与其余的扁形线虫(Rhabditophora)一起归类在Lophotrochozoa内。为了重新评估和阐明线虫的系统发育地位，用简约法和最大似然法对线虫和其他双边物种的18S核糖体DNA和线粒体基因的新序列数据进行了分析。这些分析有力地支持了线虫作为除Acoela以外的所有其他双边分类群的姊妹群在Bilateria中的基本地位。尽管线虫和棘皮虫都有基位，但枝状棘突没有被取回。这些结果表明，双边后生动物的最后一个共同祖先是一种小型底栖生物，没有节段、体腔腔、肾或真正的大脑。Nephrozoa这个名字被认为是所有双边动物的祖先，但不包括线虫和Acoela及其后代。
Recent hypotheses on metazoan phylogeny have recognized three main clades of bilaterian animals: Deuterostomia, Ecdysozoa and Lophotrochozoa. The acoelomate and 'pseudocoelomate' metazoans, including the Platyhelminthes, long considered basal bilaterians, have been referred to positions within these clades by many authors. However, a recent study based on ribosomal DNA placed the flatworm group Acoela as the sister group of all other extant bilaterian lineages. Unexpectedly, the nemertodermatid flatworms, usually considered the sister group of the Acoela together forming the Acoelomorpha, were grouped separately from the Acoela with the rest of the Platyhelminthes (the Rhabditophora) within the Lophotrochozoa. To re-evaluate and clarify the phylogenetic position of the Nemertodermatida, new sequence data from 18S ribosomal DNA and mitochondrial genes of nemertodermatid and other bilaterian species were analysed with parsimony and maximum likelihood methods. The analyses strongly support a basal position within the Bilateria for the Nemertodermatida as a sister group to all other bilaterian taxa except the Acoela. Despite the basal position of both Nemertodermatida and Acoela, the clade Acoelomorpha was not retrieved. These results imply that the last common ancestor of bilaterian metazoans was a small, benthic, direct developer without segments, coelomic cavities, nephrida or a true brain. The name Nephrozoa is proposed for the ancestor of all bilaterians excluding the Nemertodermatida and the Acoela, and its descendants.