Bifidochaetus, a new Arctic genus of freshwater Chaetonotida (Gastrotricha) from Spitsbergen revealed by an integrative taxonomic approach

Abstract

Gastrotricha is a cosmopolitan phylum of aquatic and semi-terrestrial invertebrates that comprises ~820 described species. To date, freshwater gastrotrichs have not been the subject of faunistic or taxonomic research in the polar regions. In this paper, we present the first species-level description of a freshwater gastrotrich from the Arctic (Svalbard Archipelago). Evidence from morphology, morphometry and molecular analyses reveals that the species represents a new genus in Chaetonotidae: Bifidochaetus arcticus, gen. et sp. nov. Taking into consideration many morphological similarities to Chaetonotus (Primochaetus) veronicae Kånneby, 2013 we propose to include C. (P.) veronicae in the newly established genus under the new combination Bifidochaetus veronicae (Kånneby, 2013), comb. nov. In the phylogenetic analysis based on nuclear 18S rRNA, 28S rRNA and mitochondrial cytochrome c oxidase subunit I sequence data, B. arcticus, gen. et sp. nov. is nested within the family Chaetonotidae, as the sister group to the genus Lepidochaetus Kisielewski, 1991. In this paper we also present new taxonomic characters useful for gastrotrich taxonomy: the pharynx-to-intestine length ratio (I) and the spine bifurcation ratio (B).

A new species of freshwater Chaetonotidae (Gastrotricha, Chaetonotida) from Obodska Cave (Montenegro) based on morphological and molecular characters

“…The result of our molecular phylogenetic analysis is for the greater part congruent with the previous molecular phylogenies of Chaetonotidae (Kånneby et al 2013;Kolicka et al 2016) and gave further evidence to the high degree of polyphyletism of chaetonotid genera. Freshwater species of the order Chaetonotida, which may produce opsiblastic, resting eggs, are known for passive migration with water currents, watercourses, surface run-offs, wind and being carried by more mobile animals, e.g., birds, bats, amphibians, insects or annelids (e.g., Gerlach 1977;Kolicka et al 2014).…”

“…laroides Marcolango, 1910 as the most similar taxa. Therefore, in our phylogenetic analyses we used representatives of the main clades reconstructed in the published molecular phylogeny of Chaetonotidae (Kånneby et al 2013;Kolicka et al 2016). As the outgroup we used sequences of Aspidiophorus polystictos Balsamo & Todaro, 1987, which has been reconstructed as the sister group to all other species of Chaetonotidae by Kånneby et al (2013).…”

“…The species description follows the convention of Hummon et al (1992), in which the longitudinal distance of a morphological character from the anterior end is expressed as percentage units (U) of the animal's total length (i.e., the distance of the character from the anterior end, divided by the total body length, and multiplied by 100). The identification of gastrotrichs, their morphological study and terms follows Kisielewski (1981Kisielewski ( , 1991Kisielewski ( , 1997 and Kolicka et al (2016). The terms describing the shape of furcal branches and furcal indentation follows Roszczak (1969).…”

Temperature (latitude) and nutrient (seabird guano) effects on limno-terrestrial Tardigrada (Testechiniscus spitsbergensisandPilatobius recamieri) body size

“…Until now, little attention has been given to the comparative morphometry of microscopic limno-terrestrial invertebrates living at different latitudes, especially in polar regions. While a number of recent papers have been devoted to body size in Arctic marine or freshwater invertebrates (e.g., Węsławski et al 2006;Trudnowska et al 2014;Grzelak et al 2016;Kolicka et al 2016;Hirst et al 2017), the issue remains neglected in polar limno-terrestrial microinvertebrates, with only a handful of studies performed in the Antarctic or Arctic (e.g., Jennings 1976;Zawierucha et al 2015;Seniczak et al 2017).…”

An Introduction to the Study of Gastrotricha, with a Taxonomic Key to Families and Genera of the Group

“…The following key, modified from [35], encompasses the valid families and genera of Gastrotricha (Figures 1-20) described to date [24]. Two families (Redudasyidae and Hummondasyidae, belonging to Macrodasyida) and five genera (Bifidochaetus and Cephalionotus belonging to Chaetonotida and Anandrodasys, Hummondasys, Thaidasys, and Kryptodasys belonging to Macrodasyida) included herein have been established since the publication of the previous keys [12][13][14][15]36,37]. For the inclusion of Megadasys among the Planodasyidae (order Macrodasyida), see [18].…”