Abstract
BackgroundAmong Oligohymenophorea (Ciliophora, Alveolata) the subclass Peniculia stands as one of the most well-known groups. Frontonia is the largest genus of Peniculia, and its representatives are spread in any type of water bodies as well as in soil. At a first glance, Frontonia species exhibit an overall similar morphology, and form a well-recognizable taxon of ciliates. Despite the general morphological homogeneity, the phylogenetic analysis based on the 18S rDNA sequencing showed that Frontonia is a non-monophyletic group. The systematics of this genus should be deeply reviewed, although additional issues complicate the task solving. First, type species of the genus is not yet clearly established, and no type material is available. In this context, the situation of F. vernalis, one of the first Frontonia ever described, is somehow puzzled: the description of this ciliate made by Ehrenberg (in 1833 and 1838) contains several inaccuracies and subsequent misidentifications by other authors occurred. Moreover, the 18S rDNA sequence of a putative F. vernalis is available on GenBank, but no morphological description of the correspondent specimens is provided; thus, in our opinion, it should be only prudently associated with F. vernalis or at least indicated as “F. vernalis”.ResultsIn the present work, we provide the neotypification of F. vernalis newly found in Italy, presenting its multidisciplinary description and its neotype material. Similarly, we describe a novel species bearing Chlorella-like endosymbionts, Frontonia paravernalis sp. nov., retrieved in two far distant locations (Italy, Russia). A critical discussion on the status of Frontonia taxonomy and phylogeny is also presented, based on the 18S rDNA sequencing of both these two newly collected species and other 14 frontoniids isolated in different parts of the world. Finally, in the present study F. leucas was neotypified and proposed as the type species of the genus.ConclusionsGreen frontoniids form a monophyletic clade of freshwater organisms characterized by having a single contractile vacuole and bearing intracytoplasmatic Chlorella-like symbionts. With the neotypification of F. vernalis and F. leucas a fundamental step in Frontonia systematics was taken, and the bases for further taxonomic studies were laid.
Highlights
Among Oligohymenophorea (Ciliophora, Alveolata) the subclass Peniculia stands as one of the most well-known groups
With the neotypification of F. vernalis and F. leucas a fundamental step in Frontonia systematics was taken, and the bases for further taxonomic studies were laid
After a careful and critical revision of literature and according to our research data, we propose to reject F. vernalis sensu Ehrenberg [29, 30] as a valid description and we provide the neotypification of the species, based on the newly retrieved green frontoniid population from Italy (IPSal+b)
Summary
Among Oligohymenophorea (Ciliophora, Alveolata) the subclass Peniculia stands as one of the most well-known groups. Despite the general morphological homogeneity, the phylogenetic analysis based on the 18S rDNA sequencing showed that Frontonia is a non-monophyletic group. The systematics of this genus should be deeply reviewed, additional issues complicate the task solving. Among Oligohymenophorea (Ciliophora, Alveolata) the subclass Peniculia is one of the most well-known and, in some respects, actively studied group of ciliates. Some peniculines, such as members of the Paramecium genus, serve as useful model organisms in protistology and other biological disciplines since time. Frontonia representatives are widely spread in any type of water bodies (freshwater, brackish water and marine) as well as in soil [7]
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