Fine Structure and Molecular Phylogeny of Parametopidium circumlabens (Ciliophora: Armophorea), Endocommensal of Sea Urchins

Abstract

Metopid armophoreans are ciliates commonly found in anaerobic environments worldwide; however, very little is known of their fine structure. In this study, the metopid Parametopidium circumlabens (Biggar and Wenrich 1932) Aescht, 1980, a common endocommensal of sea urchins, is investigated for the first time with emphasis on transmission electron microscopy, revealing several previously unknown elements of its morphology. Somatic dikinetids of P. circumlabens have a typical ribbon of transverse microtubules, an isolated microtubule near triplets 4 and 5 of the anterior kinetosome, plus two other microtubules between anterior and posterior kinetosomes, a short kinetodesmal striated fiber and long postciliary microtubules. In the dikinetids of the perizonal stripe, the kinetodesmal fiber is very pronounced, and there is a conspicuous microfibrillar network system associated with the kinetosomes. A new structure, shaped as a dense, roughly cylindrical mass surrounded by microtubules, is found associated with the posterior kinetosome of perizonal dikinetids. The paroral membrane is diplostichomonad and the adoral membranelles are of the "paramembranelle" type. Bayesian inference and maximum-likelihood analysis of the 18S-rDNA gene unambiguously placed P. circumlabens as sister group of the cluster formed by ((Atopospira galeata, Atopospira violacea) Metopus laminarius) + Clevelandellida, corroborating its classification within the Metopida.

Morphology and Phylogeny of the Soil Ciliate Metopus yantaiensis n. sp. (Ciliophora, Metopida), with Identification of the Intracellular Bacteria

“…; da Silva‐Neto et al. ). Nevertheless, this close relationship cannot be supported by morphological synapomorphies.…”

“…(, ) and da Silva‐Neto et al. (). Metopus yantaiensis is more closely related to M. hasei , Atopospira spp., and Parametopidium circumlabens than to other congeners in the phylogenetic trees, for which the diversification of morphological characters is not well understood (Table ).…”

“…, ; Corliss ; Da Silva‐Neto et al. ; Jankowski ,b; Lynn ). Despite about 81 species and 25 subspecies of this genus having been recorded (Roskov et al.…”

A Huge Diversity of Metopids (Ciliophora, Armophorea) in Soil from the Murray River Floodplain, Australia. II. Morphology and Morphogenesis of Lepidometopus platycephalus nov. gen., nov. spec.

“…The armophorid family Metopidae Kahl, 1927 is consistently depicted as paraphyletic since it includes the monophyletic order Clevelandellida. The "Metopidae + Clevelandellida" assemblage is very likely related to the class Litostomatea (Vďačný et al 2010;Lynn and Wright 2013;Paiva et al 2013;Bourland et al , 2017da Silva-Neto et al 2015;Li et al 2016Li et al , 2017. On the other hand, the armophorid family Caenomorphidae Poche, 1913 could be a sister group of the "Metopidae + Clevelandellida" cluster or, more likely, could have diverged at the base of the Spirotrichea or the Intramacronucleata (Paiva et al 2013).…”

“…These elegant ciliates graze bacteria in anoxic or microaerophilic environments with the aid of an obliquely extending or spiralled adoral zone of polykinetids and a tongue-like paroral membrane (Foissner et al 1992(Foissner et al , 2002Esteban et al 1995;Foissner 1998). In spite of the wide distribution and ecological significance in oxygen-depleted environments (Saccà 2012, Hu 2014, Foissner 2016a, Tirjaková et al 2016, taxonomical and morphological research on metopids has been revived only recently (e.g., Bourland et al , 2017da Silva-Neto et al 2015;Foissner 2016b, c;Omar et al 2017;Vďačný and Foissner 2017).…”