Morphologic and molecular description of Metopus fuscus Kahl from North America and new rDNA sequences from seven metopids (Armophorea, Metopidae)

Abstract

Most species in the large ciliate genus Metopus Claparède & Lachmann, 1858 lack detailed descriptions based on modern morphologic and molecular methods. This lack of data for the vast majority of species hampers application of a morphospecies approach to the taxonomy of Metopus and other armophorids. In this report we redescribe the large species, Metopus fuscus Kahl, 1927 based on in vivo observation, silver impregnation, scanning electron microscopy, and single-cell 18S rDNA sequencing of a freshwater North American (Idaho) population. Metopus fuscus invariably has a perinuclear envelope of endosymbiotic bacteria not found in other species. Unlike the original description of a single row of coarse granules between ciliary rows, the Idaho population has five loose rows of small interkinetal granules. We discuss the possible importance of this character in metopids. We also provide a phylogenetic analysis including setosus form a fully supported clade, challenging previous morphospecies groupings. We discuss some ambiguities of armophorid morphologic terminology in the earlier literature. Our phylogenetic analysis of Idaho metopids indicates that the genera Metopus and Brachonella are both nonmonophyletic.

Redescription of Atopospira galeata (Kahl, 1927) nov. comb. and A. violacea (Kahl, 1926) nov. comb. with redefinition of Atopospira Jankowski, 1964 nov. stat. and Brachonella Jankowski, 1964 (Ciliophora, Armophorida)

“…However, study of the Idaho population by DIC (in vivo), silver impregnation and SEM shows that the right and left side ribs coalesce into two slightly offset dentate processes separated by a smooth pellicular concavity giving the truncate posterior margin a bicuspid outline in dorsal and ventral views (Figs 23,f,35,(41)(42)(43). The Idaho population differs significantly from Jankowski's (1964b) pairwise difference between their 18S rDNA sequences (Bourland et al 2014;Jankowski 1964b; Kahl 1926Kahl , 1927Kahl , 1931Kahl , 1932. Atopospira violacea differs from M. fastigatus in size (95-133 vs.…”

“…A recent 18S rDNA phylogeny of morphologically characterized armophorids, including eight new single-cell metopid sequences, provided strong evidence that, at least from a molecular standpoint, the genera Metopus and Brachonella are nonmonophyletic (Bourland et al 2014). Kahl, 1926 and Brachonella galeata (Kahl, 1927) Jankowski, 1964b formed a clade with moderate to strong support in Maximum Likelihood and Bayesian analysis respectively.…”

“…These two taxa form a well-supported clade in phylogenetic analyses (Bourland et al 2014). The pair wise distance between the 18S rDNA sequences of A. galeata and A. violacea and Brachonella spiralis is 10.5% and 10.6% respectively.…”

“…Terminology is according to Bourland et al (2014), Foissner and Agatha (1999), and Lynn (2008). Suprageneric classification is according to Lynn (2008).…”

“…Over 90% of the species are classified in two of its nine genera, Metopus Claparède & Lachmann, 1858and Brachonella Jankowski, 1964a(Lynn 2008. Since the revision of Metopus by Esteban et al (1995), only a few detailed morphologic and molecular studies of metopid taxa have been published (Bourland et al 2014;Çapar 2007;Foissner and Agatha 1999;Foissner et al 2002;Vd'ačný 2007). Study of the Armophorida (i.e.…”