Integrative redescription of a common Arctic water bear Pilatobius recamieri (Richters, 1911)

Abstract

Tardigrada are a group of microscopic metazoans that inhabit a variety of ecosystems throughout the world, including polar regions, where they are a constant element of microfauna with densities exceeding hundreds of individuals per gram of dry plant material. However, despite a long history of research and their ubiquity in tundra ecosystems, the majority of tardigrade species have limited and outdated diagnoses. One such example is Pilatobius recamieri, a common tardigrade that is widely distributed in the Arctic. The aim of this study is to redescribe this species using new material from the type locality and tools of integrative taxonomy, viz. by combining classical imaging and morphometry by light microscopy and scanning electron microscopy imaging with DNA sequencing of four markers with various mutation rates: three nuclear (18S rRNA, 28S rRNA, and ITS-2) and one mitochondrial (COI). The sequences of the three latter markers are also the first to be presented for the genus Pilatobius. This study therefore provides the first necessary step towards the verification of the geographic range of P. recamieri, which is currently assumed to be very broad. A detailed comparison of P. recamieri with Pilatobius secchii (Bertolani and Rebecchi, 1996) from Italy revealed no morphological or morphometric differences between the two species, thus we designate P. secchii as a nomen inquirendum until molecular data for the taxon become available. Finally, we propose to replace the term ''lunula'' in the superfamilies Hypsibioidea and Isohypsibioidea with the more appropriate ''pseudolunula'' to differentiate it from the true lunula in other parachelans.

An integrative redescription of Hypsibius dujardini (Doyère, 1840), the nominal taxon for Hypsibioidea (Tardigrada: Eutardigrada)

“…Hypsibius valentinae, known from central and northern Belarus (Pilato et al, 2012), only by shorter external and posterior primary branches (5.9-14.0 μm in H. dujardini vs 14.5-17.2 μm in H. valentinae), and by and internal and anterior primary branches (4.6-9.4 μm in H. dujardini vs 9.3-11.5 μm in H. valentinae). Pseudolunulae under internal and anterior claws are present in both species (these structures were defined as "lunulae" in Pilato et al 2012 but the term "pseudolunula" is more appropriate to differentiate the weak cuticular outlines present under claws in hypsibiids and isohypsibiids from well-defined lunulae connected with the claw by a peduncle observed in macrobiotids and eohypsibiids; see Gąsiorek et al 2017b).…”

Deceptive conservatism of claws: distinct phyletic lineages concealed within Isohypsibioidea (Eutardigrada) revealed by molecular and morphological evidence

“…Structures were measured only if they were intact and orientated in a flat plane. Terminology for the structures within the buccal apparatus and for the claws follows that of and Gąsiorek et al (2017). Additionally, in order to avoid misunderstandings and aid comparisons between isohypsibioid taxa, we propose new terminology describing the details of the oral cavity armature (OCA); see also fig.…”

Revisiting Calohypsibiidae and Microhypsibiidae: Fractonotus Pilato, 1998 and its phylogenetic position within Isohypsibiidae (Eutardigrada: Parachela)

“…Body length was measured from the anterior to the posterior end of the body, excluding the hind legs. Terminology for the structures within the buccal apparatus and for the claws follows that of Pilato & Binda (2010) and Gąsiorek et al (2017). Gibbosity denotation system by Michalczyk & Kaczmarek (2010) was applied to the plaque arrangement.…”