Japan Agency for Marine-Earth and Technology (JAMSTEC), 2-15 Natsushima, Yokosuka, Kanagawa 237-0061, Japan.
Protist. 2013 Jan;164(1):75-88. doi: 10.1016/j.protis.2012.04.005. Epub 2012 Jun 7.
We report the ultrastructure, 18S and 28S rDNA sequences, and phylogenetic position of a distinctive free-living heterotrophic filose protist, Rigifila ramosa n. gen., n. sp., from a freshwater paddyfield. Rigifila lacks cilia and has a semi-rigid, radially symmetric, well-rounded, partially microtubule-supported, dorsal pellicle, and flat mitochodrial cristae. From a central aperture in a ventral depression emerges a protoplasmic stem that branches into several branching filopodia that draw bacteria to it. Electron microscopy reveals a general cell structure similar to Micronuclearia, the only non-flagellate previously known in Apusozoa; the large basal vacuole is probably an unusual giant contractile vacuole. Phylogenetic analysis of concatenated rDNA sequences groups Rigifila and Micronuclearia as sisters with maximal statistical support. However, novel morphological differences unique to Rigifila, notably a double (not single) proteinaceous layer beneath the cell membrane, and cortical microtubules, lead us to place it in a new family Rigifilidae. Our morphological and molecular analyses show that Rigifila is the closest known relative of Micronuclearia. Therefore we group Micronucleariidae and Rigifilidae as a new order Rigifilida within the existing class Hilomonadea, which now excludes planomonads. Rigifilida groups weakly with Collodictyon (Diphyllatea). We discuss the possible relationships of Rigifilida to other Apusozoa and Diphyllatea.
我们报告了一种独特的自由生活异养丝状原生动物——Rigifila ramosa n. gen., n. sp. 的超微结构、18S 和 28S rDNA 序列及系统发育位置，该原生动物来自淡水稻田。Rigifila 没有纤毛，具有半刚性、径向对称、圆形、部分微管支持的背披膜和扁平的线粒体嵴。从腹面凹陷的中央孔伸出一个原生质茎，该茎分支成几个分枝的丝状伪足，将细菌吸引到它那里。电子显微镜揭示了一种类似于 Micronuclearia 的一般细胞结构，这是 Apusozoa 中唯一已知的非鞭毛原生动物；大的基底液泡可能是一种不寻常的巨大收缩液泡。rDNA 序列的联合系统发育分析将 Rigifila 和 Micronuclearia 作为姐妹群，具有最大的统计支持。然而，Rigifila 具有独特的新颖形态差异，特别是细胞膜下的双层（而不是单层）蛋白质层和皮质微管，这导致我们将其置于一个新的科——Rigifilidae 中。我们的形态和分子分析表明，Rigifila 是已知的 Micronuclearia 的近亲。因此，我们将 Micronucleariidae 和 Rigifilidae 归类为现有的 Hilomonadea 类中的一个新目——Rigifilida，该目现在排除了 planomonads。Rigifilida 与 Collodictyon (Diphyllatea) 弱相关。我们讨论了 Rigifilida 与其他 Apusozoa 和 Diphyllatea 的可能关系。
