Examination of type specimens for the genera Odontella and Zygoceros (Bacillariophyceae) with evidence for the new family Odontellaceae and a description of three new genera

Abstract

Using scanning electron microscopy, Ross and Sims (1971) clarified relationships in the Biddulphiaceae and Eupodiscaceae. They identified characters that could be used to separate biddulphioid genera finding that there were two types of valve structure, poroid and loculate (alveolate), and two types of structure at the summit of the valve elevations, an ocellus and a pseudocellus; the ocellus characterised the Eupodiscaceae, its absence the Biddulphiaceae. The former is thus monophyletic. Subsequently, Ashworth et al. (2013) re-investigated the relationships of the Biddulphiaceae and Eupodiscaceae primarily using molecular evidence and showed that while the monophyly of Eupodiscaceae was supported, the species they examined currently placed in Odontella inhabit a non-monophyletic array of clades having relationships with species in genera other than Odontella. They described the new genus Trieres to include three species previously placed in Odontella, Zygoceros, Biddulphia or Denticella and they drew attention to the family Parodontellaceae as a possible synonymous collection of species. This paper presents further evidence on the relationships amongst the Eupodiscoids, particularly the fossil representatives of members of the family Parodontellaceae, and the type specimens of both Odontella and Zygoceros. We present information relevant to a new family Odontellaceae and three new genera: Pseudictyota, Hobaniella and Ralfsiella.