COI Barcoding of Nebelid Testate Amoebae (Amoebozoa: Arcellinida): Extensive Cryptic Diversity and Redefinition of the Hyalospheniidae Schultze

We used Cytochrome Oxidase Subunit 1 (COI) to assess the phylogenetic relationships and taxonomy of <i>Nebela</i> sensu stricto and similar taxa (Nebela group, Arcellinida) in order to clarify the taxonomic validity of morphological characters. The COI data not only successfully separated all studied morphospecies but also revealed the existence of several potential cryptic species. The taxonomic implications of the results are: (1) Genus <i>Nebela</i> is paraphyletic and will need to be split into at least two monophyletic assemblages when taxon sampling is further expanded. (2) Genus <i>Quadrulella</i>, one of the few arcellinid genera building its shell from self-secreted siliceous elements, and the mixotrophic <i>Hyalosphenia papilio</i> branch within the <i>Nebela</i> group in agreement with the general morphology of their shell and the presence of an organic rim around the aperture (synapomorphy for Hyalospheniidae). We thus synonymise Hyalospheniidae and Nebelidae. Hyalospheniidae takes precedence and now includes <i>Hyalosphenia</i>, <i>Quadrulella</i> (previously in the Lesquereusiidae) and all Nebelidae with the exception of <i>Argynnia</i> and <i>Physochila</i>. <i>Leptochlamys</i> is Arcellinida <i>incertae sedis</i>. We describe a new genus <i>Padaungiella</i> Lara et Todorov and a new species <i>Nebela meisterfeldi</i> n. sp. Heger et Mitchell and revise the taxonomic position (and rank) of several taxa. These results show that the traditional morphology-based taxonomy underestimates the diversity within the <i>Nebela</i> group, and that phylogenetic relationships are best inferred from shell shape rather than from the material used to build the shell.