Laboratory of Protozoology, Institute of Evolution and Marine Biodiversity, Ocean University of China, Qingdao, 266003, China.
Sci China Life Sci. 2011 Jul;54(7):634-41. doi: 10.1007/s11427-011-4192-8. Epub 2011 Jul 12.
Discocephalids and pseudoamphisiellids are possibly two of the most confused groups among hypotrichous/euplotid ciliates regarding their systematic position and phylogenetic relationships. The former were often regarded as related to euplotids while the latter, in the absence of molecular data, were mostly assigned to the urostylid-like hypotrichs. In the present work, the small subunit rRNA genes of several rarely observed discocephalid and pseudoamphisiellid genera were analyzed to obtain insights into the phylogenetic relationships of these highly ambiguous Spirotrichea. Four different tree reconstruction algorithms yielded nearly identical topologies, which indicated both groups belong to the same assemblage. This assemblage is clearly isolated as a deep-branching clade and invariably positioned between Euplotida and Hypotricha. The sister group relationship of the Pseudoamphisiellidae and Discocephalidae supports the previous suggestion that they might represent an ordinal taxon, the Discocephalida. Both morphological and morphogenetic features indicate that the pseudoamphisiellids should be placed in the order Discocephalida but as a sister group to other typical discocephalids. Thus we propose establishing a new suborder, Pseudoamphisiellina subord. n. The new taxon is diagnosed by the following characteristics: (i) two distantly separated midventral rows that are morphogenetically formed with an urostylid mode; (ii) absence of the "frontoterminal row", which is formed from the posterior-most frontoventral-transverse cirral anlage in all other typical urostylids; (iii) numerous caudal cirri that derive from each of the dorsal kinety anlagen; (iv) right marginal row that has a unique de novo origin; and (v) inhabiting periphytic communities. The validity of the suborder Pseudoamphisiellina is firmly supported by molecular data.
盘蜷目和伪胶口目可能是纤毛亚门腹毛目下最混乱的两个群体，在系统发育位置和系统发生关系上存在争议。前者通常被认为与腹毛类有关，而后者由于缺乏分子数据，大多被归入类似尿毛类的纤毛类。本研究分析了少数罕见的盘蜷目和伪胶口目属的小亚基 rRNA 基因，以深入了解这些高度模糊的旋毛类的系统发育关系。四种不同的树重建算法产生了几乎相同的拓扑结构，这表明这两个群体属于同一集合体。该集合体作为一个深分支聚类被清晰地分离出来，并且始终位于腹毛目和真毛目之间。伪胶口目和盘蜷目具有姐妹群关系，支持了它们可能代表一个目级分类单元——盘蜷目的先前建议。形态和形态发生特征都表明，伪胶口目应该归入盘蜷目，但作为其他典型盘蜷目的姐妹群。因此，我们建议建立一个新的亚目，即伪胶口目亚目。新分类单元的特征如下：（i）两个相距较远的中腹行，以尿毛目模式形成；（ii）不存在“前顶行”，前顶行是所有其他典型尿毛目中由最前的额腹横向纤毛原基形成的；（iii）许多尾纤毛起源于每个背纤毛原基；（iv）右缘行具有独特的从头起源；（v）栖息于周丛群落。伪胶口目亚目的有效性得到了分子数据的有力支持。
