Systematic review of the genus Ostracodinium (Ciliophora, Entodiniomorphida, Ophryoscolecidae) and notes on the taxonomy of Ostracodinium rugoloricatum Kofoid & MacLennan, 1932

Abstract

The family Ophryoscolecidae (Ciliophora, Entodiniomorphida) constitutes a diverse and monophyletic group of symbiotic ciliates of herbivorous mammals. The family includes approximately 200 species, distributed in three subfamilies and sixteen genera. The subfamily Diplodiniinae is the most diverse group in Ophryoscolecidae and comprises the genus Ostracodinium, which includes species with two retractable ciliary zones in the anterior body portion, a broad skeletal plate covering almost all the right surface of the body and a variable number of contractile vacuoles. The genus currently comprises 28 species, classified according to body size and shape, position and shape of the nuclear apparatus, number and position of contractile vacuoles, and number and shape of caudal projections. The present study performs a systematic review of the genus Ostracodinium, based on morphological and molecular data, and provides data about geographic distribution and hosts of each species.

Insights into the systematics of the family Ophryoscolecidae (Ciliophora, Entodiniomorphida)

“…According to her, the infraciliary band morphology of the genus Diplodinium sensu Dogiel corroborates Dogiel's systematics (Dogiel, 1927), since all Diplodinium sensu Dogiel species share the same pattern of infraciliary bands. However, it has been demonstrated, recently, that some ophryoscolecids, such as Metadinium , Ostracodinium , and Eodinium representatives have distinct infraciliary band morphologies (Cedrola et al, 2018, 2021; Gürelli & Akman, 2017; Ito & Imai, 1998, 2003; Ito et al, 2001), contradicting Dogiel (1927) and Noirot‐Timothée (1960) hypotheses.…”

“…Recently, some studies revised the systematics of some Ophryoscolecidae genera [ Diplodinium , Diploplastron , Ostracodinium , and Metadinium Cedrola et al, 2017a, b, 2018, 2021] and according to molecular phylogenetic reconstructions (Cedrola, Senra, et al, 2017; Cedrola et al, 2020; Rossi et al, 2015), the systematics of the family needs reconsideration, as many of the classification available do not reflect evolutionary divergences.…”

“…In fact, according to Cedrola, Senra, et al (2017) the evolutionary signal of the 18S rDNA is insufficient to reconstruct intra‐family relationships within Ophryoscolecidae. Recent studies have recently revised the classification of the genera Diplodinium , Diploplastron , Metadinium , and Ostracodinium (Cedrola et al 2017a, b, 2018, 2021), and here, we complemented the discussion with considerations of the validity of the genera Elytroplastron and Eremoplastron , and on the phylogenetic position of D . polygonale .…”

“…In fact, according to Cedrola, Senra, et al (2017) the evolutionary signal of the 18S rDNA is insufficient to reconstruct intra-family relationships within Ophryoscolecidae. Recent studies have recently revised the classification of the genera Diplodinium, Diploplastron, Metadinium, and Ostracodinium (Cedrola et al 2017a(Cedrola et al , b, 2018(Cedrola et al , 2021, and here, we complemented the discussion with considerations of the validity of the genera Elytroplastron and Eremoplastron, and on the phylogenetic position of D. polygonale. We conclude that integrative approaches, using ultrastructural data and multigene phylogenies or phylogenomics are necessary to better understand the evolutionary relationships within Ophryoscolecidae and improve its systematics.…”

“…The most recent systematic review of the family was performed 55 years ago (Latteur, 1966) and only recently, some studies revised the systematics of part of its genera, such as Diplodinium Schuberg, 1888, Diploplastron Kofoid & MacLennan, 1932, Metadinium Awerinzew & Mutafowa, 1914, and Ostracodinium Dogiel, 1927 (Cedrola et al, 2017a, b, 2018, 2021) and discussed systematic incongruences based on molecular analyses (Cedrola, Senra, et al, 2017; Cedrola et al, 2020; Rossi et al, 2015). These papers stress that a far‐reaching revision of the systematics of this family is required, indicating that the current taxonomy does not reflect evolutionary relationships and is insufficient to organize the diversity of the group (Dogiel, 1927; Kofoid & MacLennan, 1930, 1932, 1933).…”