When DNA sequence data and morphological results fit together: Phylogenetic position of Crenubiotus within Macrobiotoidea (Eutardigrada) with description of Crenubiotus ruhesteini sp. nov

Advances in bioinformatic approaches to tardigrade phylogeny

The quest to discover the evolutionary relationships of organisms is an evolving, long-time topic of research. Such research gave rise to many different taxonomic databases and various definitions of systematic groups. One such group is the phylum Tardigrada. Tardigrades are an important field of study because of their biotechnological potential as well as their complex biological processes, which have the potential to answer questions about animal evolution. The evolutionary relationships within the phyla are subject to rigorous research, and new data is added to the literature constantly. For these studies, a widespread technique is the use of bioinformatic approaches in order to put forward concrete phylogenetic evidence. Bioinformatics is a field of computational biology that interprets large amounts of data in order to compute and demonstrate results. It is widely used not only for phylogeny but also for various different types of analyses and has been growing as a field since its foundation. This review discusses the different aspects, advantages, and methods of the use of bioinformatics in tardigrade phylogeny. It aims to put forward a defining picture of how the bioinformatic methods prove useful for providing phylogenetic results and elaborate on future perspectives.

A new, simplified, drying protocol to prepare tardigrades for scanning electron microscopy

A new protocol for preparation of tardigrades for scanning electron microscope (SEM) analysis is proposed. The more conventional protocols require various steps and a long time to obtain good drying of water bears, together with specific and uncommon instruments (i.e., critical point dryer) or highly volatile toxic compounds (i.e., hexametildisilazane). The new protocol can be performed using few and simple instruments and materials, all easily accessible, and produces a high yield in terms of dried animals in excellent condition for the observation of external morphological structures with SEM. The acquired data exhibit considerable promise, and the proposed methodology shows potential for application to other meiofaunal groups, including small arthropods, nematodes, and rotifers. RESEARCH HIGHLIGHTS: Cheap, safe, and fast new method for Tardigrada preparation for SEM. With the new protocol, the number of animals required for SEM studies is minimized. New protocol is potentially applicable to the study of other meiofaunal soft-bodied taxa.

Integrative taxonomy helps to revise systematics and questions the purported cosmopolitan nature of the type species within the genus Diaforobiotus (Eutardigrada: Richtersiusidae)

Recent advances in tardigrade taxonomy have been greatly enhanced by the redescriptions of the type species for particular taxa or species groups. De novo characterisation of these key taxa now allows to describe tardigrade species diversity with improved precision and at higher rate, increasing the momentum towards resolving the taxonomic impediment in these micro-invertebrates. Since its description, Diaforobiotus islandicus (Richters, 1904) has been reported from many distinct localities around the world. This suggested, perhaps falsely, a cosmopolitan nature of the species. However, potential erroneous assignment of newly found populations to this species could be a result of the very general and superficial original description. In order to properly recognise and name species diversity within the genus, I provide here an integrative redescription of the type species (D. islandicus) with a neotype designation, a description of a new species, Diaforbiotus svalbardicus sp. nov, and dichotomous key for the genus. Both descriptions are based on detailed morphological and morphometric data associated with standard DNA sequences of four genetic markers (18S rRNA, 28S rRNA, ITS-2, and COI). The genus composition and diagnosis amendments of the family Richtersiuside are also discussed. The presented study constitutes a starting point for further systematic studies on the genus Diaforobiotus and new taxa discoveries.

An integrative description of a new Richtersius species from Greece (Tardigrada: Eutardigrada: Richtersiusidae)

In this paper, we describe a new tardigrade species, Richtersius tertius sp. n., from Greece. The description is based on morphological and morphometric analysis using light and scanning electron microscopy as well as genetic analysis based on four molecular markers (DNA sequences of three nuclear, i.e., 18S rRNA, 28S rRNA, ITS-2 and one mitochondrial COI fragment). Morphological and morphometric differences, together with genetic comparisons, provide independent verifications of Richtersius tertius sp. n. as a species new to science. Phenotypically, the new taxon differs from Richtersius coronifer (Richters, 1903) and Richtersius ziemowiti Kayastha, Berdi, Miaduchowska, Gawlak, Łukasiewicz, Gołdyn, Jędrzejewski et Kaczmarek, 2020 mainly by the morphology and size of cuticular pores, present only in hatchlings (first instars), as well as some morphometric characters. The results presented herein contribute further to the recognition of the morphological variability and biodiversity within Richtersius, with Richtersius tertius sp. n. being the third species formally described within the genus.

Reaching the Monophyly: Re-Evaluation of the Enigmatic Species Tenuibiotus hyperonyx (Maucci, 1983) and the Genus Tenuibiotus (Eutardigrada)

Revisions and redescriptions of taxa described in the past and that are now categorized as insufficiently diagnosed often play a crucial role in making further progress in modern taxonomy in many groups of organisms. Here we revised an enigmatic tardigrade species Tenuibiotus hyperonyx (Maucci, 1983) based on the newly discovered topotypic population from the Italian Alps. We performed an integrative analysis of morphological and genetic data in order to present an upgraded species description and elucidate its phylogenetic position. Our results enabled us to confidently place T.hyperonyx within the family Richtersiusidae, as a member of the genus Diaforobiotus. This change, together with a re-assessment of microphotographs of the Tenuibiotus willardi (Pilato, 1977) and Tenuibiotus bozhkae Pilato, Kiosya, Lisi, Inshina & Biserov, 2011 types, led to the discussion on species composition with narrative taxa amendments for the taxonomic parties involved in the proposed alteration.

Integrative descriptions of two new Macrobiotus species (Tardigrada, Eutardigrada, Macrobiotidae) from Mississippi (USA) and Crete (Greece)

In this paper, we describe two new Macrobiotus species from Mississippi (USA) and Crete (Greece) by means of integrative taxonomy. Detailed morphological data from light and scanning electron microscopy, as well as molecular data (sequences of four genetic markers: 18S rRNA, 28S rRNA, ITS-2 and COI), are provided in support of the descriptions of the new species. Macrobiotus annewintersaesp. nov. from Mississippi belongs to the Macrobiotus persimilis complex (Macrobiotus clade B) and exhibits a unique egg processes morphology, similar only to Macrobiotus anemone Meyer, Domingue & Hinton, 2014, but mainly differs from that species by the presence of eyes, granulation on all legs, dentate lunulae on legs IV, and of bubble-like structures within the tentacular arms that are present on the distal portion of the egg processes. Macrobiotus rybakisp. nov. from Crete belongs to the Macrobiotus clade A and is most similar to Macrobiotus dariae Pilato & Bertolani, 2004, Macrobiotus noemiae Roszkowska & Kaczmarek, 2019, Macrobiotus santoroi Pilato & D’Urso, 1976, and Macrobiotus serratus Bertolani, Guidi & Rebecchi, 1996, but differs from them mainly in the morphological details of its egg processes and chorion reticulation, but also by a number of morphometric characters. In light of the specific morphology of the egg processes of Macrobiotus annewintersaesp. nov. and Macrobiotus anemone, that are equipped with tentacular arms instead of proper terminal disc, we also provide an updated definition of the Macrobiotus persimilis complex.