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首页> 外文期刊>Belgian Journal of Zoology >First record of Nemertodermatida from Belgian marine waters
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First record of Nemertodermatida from Belgian marine waters

机译：比利时海水中的奈瑟氏菌的首次记录

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摘要

Nemertodermatida is a small taxon of marine worms, comprising only eight described species. They are charac-terised by a nemertine-like epidermis (hence the name) and a statocyst containing (mostly) two statoliths (1). The phylogenetic relationships of the taxon have been (and still are) the subject of debate. Initially, they were placed within the acoel Platyhelminthes (2), but Karling (1, 3) considered them to be substantially different from the acoels in morphology of the gut and the statocyst, and placed the taxon Nemertodermatida outside the Acoela (3). In the first phylogenetic analysis of the Platyhelminthes by Ehlers (4), Nemertodermatida formed a sister group relationship with Acoela, together forming the taxon Acoelomorpha, at that time considered to be the sister group of Rhabditophora (4). This view was followed in most subsequent morphological studies (for a review: see 5). Smith et al. (6) suggested the possible polyphyly of the taxon Platyhelminthes, based on the absence of clear synapomorphies, and viewed the Acoelomorpha as one of the three well-defined monophyletic groups within the Platyhelminthes, the two others being Catenulida and Rhabditophora. Recent molecular phylogenetic studies (7 ; 8) corroborate the polyphyly of the Platyhelminthes and show the Nemertodermatida and the Acoela in a basal position within Bilateria. The presence of the small Hox cluster in both Acoela (9) and Nemertodermatida (10) is concordant with this phylogenetic position. Based on analyses of 18S rRNA and mitochondrial genes (7) and 18S and 28S rRNA sequences (11), the taxon Acoelomorpha was dismissed because it appeared to be paraphyletic ; Nemertodermatida and Acoela are separate branches at the base of the Bilateria. A recent phylogeny based on a large number of taxa and multiple nuclear genes, however, provides support for a monophyletic Acoelomorpha, albeit also ositioned at the base of the Bilateria (12). Because of this basal phylogenetic position, the study of Nemertodermatida is important for the understanding of the characteristics of the bilaterian ancestor (11) and it makes them important study-objects for morphologists and molecular biologists alike. Note that the latest study on the phylogenetic position of Acoe-lomorpha (13) challenges their basal position and places them within the Deuterostomia, together with Xenotur-bella. In the most recent comprehensive taxonomic over-view of Nemertodermatida (14), Sterrer revealed consid-erable intraspecific variation for characters such as size, colour, presence/absence of glands, etc. Hence, species delimitation is often problematic and also cryptic diver-sity cannot be excluded, which makes nemertodermatids also interesting from a (molecular) taxonomical point of view. Regrettably, Nemertodermatida are known from a few distinct sampling spots only: the Swedish west coast, the east coast of North America, the Adriatic and the Mediterranean, which suggests that representatives of the taxon are difficult to collect.
机译：Nemertodermatida是一种海洋蠕虫的小类群，仅包含8个描述的物种。它们的特征是有一个nemertine状的表皮（因此得名）和一个包含（大部分）两个吻合石的吻合囊（1）。分类单元的系统发育关系一直是（并且仍然是）争论的话题。最初，它们被放置在鸭嘴兽的侧翼（2）中，但Karling（1、3）认为它们在肠道和囊肿的形态上与鸭嘴兽有显着差异，并将分类器（Nemertodermatida）放置在鸭嘴兽（3）之外。在Ehlers（4）首次对侧柏进行系统发育分析时，Nemertodermatida与Acoela形成了姐妹群关系，一起形成了分类单元Acoelomorpha，当时被认为是Rhabditophora的姐妹群（4）。在随后的大多数形态学研究中都遵循了这种观点（综述：参见5）。史密斯等。 （6）基于不存在清晰的同形亚型，提出了类群侧柏的可能的复系，并认为侧耳畸形是侧柏中三个明确定义的单系群之一，另外两个是Catenulida和Rhabditophora。最近的分子系统发育研究（7; 8）证实了侧柏的多重性，并显示Nemertodermatida和Acoela位于Bilateria的基础位置。在Acoela（9）和Nemertodermatida（10）中都存在小的Hox簇与这种系统发育位置一致。根据对18S rRNA和线粒体基因（7）以及18S和28S rRNA序列（11）的分析，分类单元Acoelomorpha被抛弃了，因为它似乎是类共生的。 Nemertodermatida和Acoela是Bilateria底部的独立分支。然而，最近的系统发育基于大量的分类单元和多个核基因，为单系的Acoelomorpha提供了支持，尽管它也位于Bilateria的基部（12）。由于这种基础的系统发育位置，对奈米皮肤病科的研究对于了解双语生物祖先的特征非常重要（11），这使其成为形态学家和分子生物学家的重要研究对象。请注意，有关Acoe-lomorpha（13）的系统发生位置的最新研究挑战了它们的基础位置，并将它们与Xenotur-bella一起放置在Deuterostomia中。在对奈莫氏皮肤病科的最新综合分类学概述中（14），Sterrer揭示了诸如字符的大小，颜色，腺体的存在/不存在等特征的种内差异很大。因此，物种划界常常是有问题的，并且也是隐秘的不能排除单一性，从（分子）生物分类学的角度来看，这也使线虫病变得有趣。遗憾的是，仅从几个不同的采样点就知道了奈瑟氏皮肤病：瑞典的西海岸，北美的东海岸，亚得里亚海和地中海，这表明该分类单元的代表很难收集。

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