Abstract
Hypotrich ciliates with evolutionary novelties are continually being discovered, challenging the current taxonomic system and attracting increased attention. In the present work, two new urostylid ciliates, Heterobakuella bergeri gen. nov., sp. nov. and Anteholosticha perezuzae sp. nov., isolated from Chinese wetland samples, were identified based on morphology and 18S rRNA gene sequences. Heterobakuella gen. nov. is defined by three frontal cirri, single buccal cirrus, one parabuccal cirrus, midventral complex composed of cirral pairs and one cirral row, one left and two right marginal cirral rows, transverse and pretransverse cirri present, caudal and frontoterminal cirri absent. Heterobakuella can be easily distinguished from the morphologically most similar genus, Apobakuella, mainly by the single buccal cirrus (vs. one buccal cirral row) and one parabuccal cirrus (vs. several parabuccal cirral rows originated from different anlagen). Phylogenetic analyses show that H. bergeri branches within the clade formed by Bergeriella ovata, Monocoronella carnea, Anteholosticha gracilis, and Neourostylopsis spp., rather than the clade represented by Apobakuella. The other species, A. perezuzae, is mainly characterized by a distinctly slender body shape with an average length:width ratio about 7, distinctively shaped biconcave and greenish cortical granules, as well as one or two pretransverse cirri. Phylogenetic analyses indicate the genus Anteholosticha is non-monophyletic.
Highlights
According to Berger (2006), some urostylid taxa characterized by having three frontal cirri and a midventral complex composed of cirral pairs in the anterior portion and at least one cirral row in the posterior portion were assigned to the family Bakuellidae
Seven urostylid genera with a continuous adoral zone, three frontal cirri, and midventral complex composed of cirral pairs and row(s) should be compared with Heterobakuella gen. nov., namely, Apobakuella, Bakuella, Holostichides, Metaurostylopsis, Monourostylopsis Song et al, 2020, Neobakuella, and Paragastrostyla (Berger, 2006; Li et al, 2011; Jiang et al, 2013; Song et al, 2020; Figure 8)
Heterobakuella gen. nov. can be separated from Holostichides and Paragastrostyla by transverse cirri (Berger, 2006; Zhu et al, 2019), and from the other four genera by marginal cirral rows, frontoterminal cirri (Li et al, 2011; Jo et al, 2015; Lu et al, 2016; Moon et al, 2020; Song et al, 2020; Zhang et al, 2020b)
Summary
Hypotrichia Stein, 1859, is a large group of ciliated protists with extremely diverse morphologic and morphogenetic characters, with worldwide distribution in diverse habitats, including marine and fresh waters, and even desert soils (Berger, 1999, 2006, 2008, 2011; Foissner, 2016; Hu et al, 2019; Jung and Berger, 2019; Kaur et al, 2019; Kim and Min, 2019; Wang et al, 2020a,b; Chen et al, 2021; Luo et al, 2021; Two Novel Urostylid CiliatesMa et al, 2021; Song et al, 2021; Vd’acný and Foissner, 2021; Wang et al, 2021). Studies from the past few decades have revealed that this group is even more diverse than previously thought, and many new species are likely awaiting discovery (Berger, 2006; Jiang et al, 2013; Jo et al, 2015; Kim et al, 2016; Song and Shao, 2017; Chen et al, 2018, 2020; Zhu et al, 2019; Shao et al, 2020; Xu et al, 2020; Zhang et al, 2020a). New bakuellid-like taxa with evolutionary novelties are regularly being discovered, which renders the classification of the bakuellid-like taxa difficult in practice
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