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Background <p>As unicellular eukaryotes, ciliates are indispensable components of ecosystems, serving as an intermediate nutrition link between bacteria or algae and meiofauna. The class Nassophorea Small and Lynn, 1981 is a group of morphologically specialized ciliates characterized by a basket-like cytopharynx supported by thick microtubular rods, which are algivorous and thus act as primary consumers in ecosystems. In the present study, the morphology and molecular phylogeny of three new nassulid ciliates were studied based on morphological and small subunit ribosomal ribonucleic acid gene sequence data. The secondary structure of the V9 region of their 18S rRNA gene sequences was also analyzed to investigate their phylogenetic relationships.</p> Results <p>Based on morphological feature and phylogenetic analysis, we establish a new genus <i>Aponassulides</i> gen. nov. and discovered three new species, viz. <i>Aponassulides lacustris</i> gen. nov., sp. nov., <i>Naxella vorax</i> sp. nov. and <i>Nassula paralabiata</i> sp. nov. The new genus is distinguished from its relatives by having nassulid organelles orientated obliquely to frange axis and diagonally along the top left and bottom right directions. <i>Aponassulides lacustris</i> gen. nov., sp. nov. can be recognized by its large-sized and broadly rounded body and linear nassulid frange orientated by numerous nassulid organelles as well freshwater habitat. <i>Naxella vorax</i> sp. nov. is characterized by having a medium-sized and broadly ellipsoidal body, three or four nassulid organelles and 55–68 somatic kineties. <i>Nassula paralabiata</i> sp. nov. is a marine species with sigmoidal nassulid frange, three caudal cilia and two lip-shaped cytoplasmic membranes. Phylogenetic analyses revealed that three new species clusters within the family Nassulidae de Fromentel, 1874. The analysis of the secondary structure of the SSU rRNA V9 region is also consistent with the topology of the phylogenetic tree.</p> Conclusions <p>The study of the morphology of three new nassulids increases the overall knowledge about the biodiversity of this ciliate group. It also adds to the genetic data available, substantiates the paraphyly of the Nassulida, and recovers the monophylies of genera <i>Naxella</i> and <i>Nassula</i> for the first time.</p>

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Taxonomy and molecular phylogeny of nassulid ciliates (Alveolata, Ciliophora) with descriptions of one new genus and three new species

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  • 发表日期：

    2025年12月9日

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  • Qianhui Sun,
  • Limin Jiang,
  • Mingjian Liu,
  • Xiaozhong Hu

摘要

Background

As unicellular eukaryotes, ciliates are indispensable components of ecosystems, serving as an intermediate nutrition link between bacteria or algae and meiofauna. The class Nassophorea Small and Lynn, 1981 is a group of morphologically specialized ciliates characterized by a basket-like cytopharynx supported by thick microtubular rods, which are algivorous and thus act as primary consumers in ecosystems. In the present study, the morphology and molecular phylogeny of three new nassulid ciliates were studied based on morphological and small subunit ribosomal ribonucleic acid gene sequence data. The secondary structure of the V9 region of their 18S rRNA gene sequences was also analyzed to investigate their phylogenetic relationships.

Results

Based on morphological feature and phylogenetic analysis, we establish a new genus Aponassulides gen. nov. and discovered three new species, viz. Aponassulides lacustris gen. nov., sp. nov., Naxella vorax sp. nov. and Nassula paralabiata sp. nov. The new genus is distinguished from its relatives by having nassulid organelles orientated obliquely to frange axis and diagonally along the top left and bottom right directions. Aponassulides lacustris gen. nov., sp. nov. can be recognized by its large-sized and broadly rounded body and linear nassulid frange orientated by numerous nassulid organelles as well freshwater habitat. Naxella vorax sp. nov. is characterized by having a medium-sized and broadly ellipsoidal body, three or four nassulid organelles and 55–68 somatic kineties. Nassula paralabiata sp. nov. is a marine species with sigmoidal nassulid frange, three caudal cilia and two lip-shaped cytoplasmic membranes. Phylogenetic analyses revealed that three new species clusters within the family Nassulidae de Fromentel, 1874. The analysis of the secondary structure of the SSU rRNA V9 region is also consistent with the topology of the phylogenetic tree.

Conclusions

The study of the morphology of three new nassulids increases the overall knowledge about the biodiversity of this ciliate group. It also adds to the genetic data available, substantiates the paraphyly of the Nassulida, and recovers the monophylies of genera Naxella and Nassula for the first time.