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a long history of research and their ubiquity in tundra ecosystems, the majority of tardigrade species have limited and outdated diagnoses.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.
Highlights
The tardigrades, known as water bears, are common micrometazoans, usually less than 1 mm in length
Specimens for light microscopy and morphometry were mounted on microscope slides in a small drop of Hoyer’s medium prepared according to Morek et al (2016) and examined under a Nikon Eclipse 50i phase-contrast microscope (PCM) associated with a Nikon Digital Sight DS-L2 digital camera
Twenty-five years later, Marcus (1936) analyzed specimens from Spitsbergen and noted that they have a microplacoid and that P. recamieri can be differentiated from P. oculatus (Murray, 1906) by the length of the pharyngeal tube, and internal claw morphology
Summary
The tardigrades, known as water bears, are common micrometazoans, usually less than 1 mm in length They are distributed across the globe, inhabiting a great majority of terrestrial (soil, plants, and leaf litter), freshwater, and marine ecosystems (plants, coastal and deep-oceanic sediments), from tropical and temperate regions to the highest mountain peaks, glaciers, and polar deserts (e.g., Nelson et al 2015). They are widely known for their cryptobiotic capabilities, thanks to which they can withstand extreme conditions such as low and high temperatures, desiccation, and high ultraviolet radiation doses (e.g. Guidetti et al 2012). Studies of Svalbardian tardigrades began in the late 19th century (Scourfield 1897) and have been
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
