Evolution of discocephalid ciliates: Molecular, morphological and ontogenetic data support a sister group of discocephalids and pseudoamphisiellids (Protozoa, Ciliophora) with establishment of a new suborder Pseudoamphisiellina subord. n.

Abstract

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. Ciliophora, Discocephalida, Pseudoamphisiellina subord. n., new suborder, phylogeny, SSU rRNA gene Citation:Miao M, Shao C, Chen X M, et al. Evolution of discocephalid ciliates: Molecular, morphological and ontogenetic data support a sister group of discocephalids and pseudoamphisiellids (Protozoa, Ciliophora) with establishment of a new suborder Pseudoamphisiellina subord. n

Description and Phylogeny of Tetrakeronopsis silvanetoi gen. nov., sp. nov. (Hypotricha, Pseudokeronopsidae), a New Benthic Marine Ciliate from Brazil

“…In addition, the spreading of Anteholosticha spp. among various clusters also corroborates previous phylogenetic studies on urostyloids [23], [24], [26], [27], [45]. The heterogeneity of the genus Anteholosticha was already pointed out by Berger [2], [46].…”

“…[20]–[24], [26]. Seven additional sequences of representatives of Discocephalida Wicklow, 1982, sensu [27] were included as an outgroup [25]–[27]. The sequences were aligned based on their eukaryotic 18S-rRNA secondary structure, using the SINA web aligner (http://www.arb-silva.de/aligner) [28] with its default settings.…”

Evolution of the Order Urostylida (Protozoa, Ciliophora): New Hypotheses Based on Multi-Gene Information and Identification of Localized Incongruence

“…Our analyses firmly support the conclusion that this family should be excluded from the order Urostylida, but rather belongs to a group of its own which clusters to the well-known discocephalids [23], [48].…”

Morphogenesis and Molecular Phylogeny of a New Freshwater Ciliate, Notohymena apoaustralis n. sp. (Ciliophora, Oxytrichidae)

“…Likewise, increased availability of sequences of other genes (e.g. ITS, LSU rDNA, tubulin) may also help resolve phylogenetic relationships within this group (Huang et al 2012;Miao et al 2011;Yi and Song 2011).…”