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The 15th International Symposium on Tardigrada, held in Kraków, Poland, brought together researchers from around the world to discuss various topics related to tardigrades. The symposium featured lectures, poster presentations, and a taxonomic roundtable, providing a platform for researchers to share their findings and engage in discussions about the future of tardigrade research. The main point of contention among researchers is the use of DNA analysis in studying tardigrades, with some arguing for the need to switch to integrative taxonomy and others believing that both approaches are valid. The symposium also recognized outstanding young scientists and included the presentation of a bell and distribution of tardigrade-themed souvenirs. The proceedings of the symposium cover a wide range of topics, including DNA analysis, taxonomy, ecology, morphology, and physiology, providing valuable insights into the biology and ecology of tardigrades and highlighting the need for further research in this field. [Extracted from the article]

Tardigrade taxonomy is most often hindered by prevalent outdated species descriptions, lack of integrative redescriptions, scarce genetic information, and fragmentary sampling. Here, we diagnose the problems obscuring phylogenetic inference and the taxonomy of the cosmopolitan family Ramazzottiidae. We carried out the most extensive phylogenetic analysis of this family to date, with a considerable influx of new genetic data from poorly sampled regions of the world. We found two new distinct evolutionary lineages defined by distinct morphological traits (dorsal cuticular sculpturing and/or body shape), characterized by restricted geographic distributions, and we delineated them as new species complexes: the Neotropical Ramazzottius baumanni complex and the Afro-Oriental Ramazzottius szeptyckii complex. Nevertheless, we could not confidently ascertain the taxonomic status of both complexes due to: (i) the current state of the ramazzottiid taxonomy, with outdated and/or imprecise species descriptions with heterogeneous terminology and, in many cases, without accounting for intraspecific variation; (ii) the missing genetic information for key taxa; and (iii) the possible lack of monophyly of Cryoconicus and Ramazzottius as suggested by our results. In addition to diagnosing the problems of ramazzottiid phylogeny and systematics, we also propose possible solutions that could accelerate the progress in our understanding of the evolution of this group. [ABSTRACT FROM AUTHOR]

Green, brown and black pigments are uncommon in the otherwise typically yellow to orange Echiniscidae. Viridiscus , a genus currently represented by a handful of species, in which cuticular coloration varies from a light green through dark green to almost black, has been an exception. Here, we uncover a new echiniscid lineage from the primeval subtropical and tropical rainforests of India and Tanzania, comprising three species with a caramel/brown body. Given that both Viridiscus and the new species complex lack dorsolateral trunk appendages and share dark cuticular pigmentation, they may be mistaken for each other. However, a closer inspection of the dorsal cuticular sculpture and molecular phylogenetic analyses indicate that the new complex belongs within the Echiniscus spinulosus morphogroup. Thus, the presence of dark pigments in two indirectly related lineages is evidence for the convergence of dark cuticular coloration in limno-terrestrial heterotardigrades. We detected three species in the new complex: Echiniscus brunus sp. nov. from the Western Ghats (Tamil Nadu, India), and two other candidate species, Echiniscus aff. brunus sp. can. 1 and Echiniscus aff. brunus sp. can. 2, from India and Tanzania, respectively. We refrain from describing the two latter species formally because they exhibit little or no morphological differences, which is yet another clear case of the crucial role of DNA barcoding in an accurate estimation of tardigrade species richness. [ABSTRACT FROM AUTHOR]

Numerous evolutionary lineages representing an armoured, limno-terrestrial family Echiniscidae are restricted to high mountainous or polar localities, exhibiting clear cold stenothermic preferences. One such group is the genus Claxtonia , with its type species Claxtonia wendti , originally described from Svalbard and later on reported globally. In this paper, we re-describe this taxon by establishing the neotype from Spitsbergen. We sequenced five genetic markers (18S rRNA, 28S rRNA, ITS-1, ITS-2, and COI) for multiple populations of Claxtonia , including C. mauccii , C. molluscorum , C. wendti , and several potentially new species, collected in the Alps, Andes, Carpathians, Scotland, Iceland, Southern Appalachians, Spitsbergen, Scandinavian Peninsula, Borneo, and the West Indies. The relationships between these species are elucidated thanks to the phylogenetic reconstructions based on nuclear loci. Various Claxtonia species frequently co-occur in mosses and lichens, which hampers delineating their probable geographic ranges. All historical records of C. wendti are questioned in the light of our revision. Delineation of new species within the genus is nipped in the bud due to numerous problems with original species descriptions, unknown intraspecific (including ontogenetic) variability, and the lack of DNA barcodes. Finally, it is hypothesized that Claxtonia potentially comprises two lineages: a cold-stenothermic one and a thermophilic subtropical–tropical one. [ABSTRACT FROM AUTHOR]

The recent integrative revision of the family Macrobiotidae demonstrated monophyly of the genus Macrobiotus and its complex, mosaic morphological evolution. Here, we analyse three Macrobiotus populations that exhibit extraordinary claw morphology characterized by elongated primary branches. Two of these populations, from the Arctic, were initially classified as Macrobiotus ariekammensis , but detailed integrative analyses resulted in splitting them into two subspecies: Macrobiotus ariekammensis ariekammensis and Macrobiotus ariekammensis groenlandicus subsp. nov.. The third population was Macrobiotus kirghizicus from Kyrgyzstan. Given the unusual phenotype of the above-mentioned taxa, we tested whether they constitute a distinct lineage in the family Macrobiotidae and could be delineated as a new genus. Although the phylogenetic investigation showed that the three taxa form a monophyletic group, the clade is nested in the genus Macrobiotus. Therefore, despite their morphological distinctiveness, a new genus cannot be established and we group these taxa in the Macrobiotus ariekammensis species complex instead. The complex includes the three above-mentioned taxa and Macrobiotus ramoli , which is included based on morphological characters. Moreover, our results provide evidence for rapid parallel evolution of long claws in macrobiotid tardigrades inhabiting cold and icy environments. Finally, we discuss the validity of the recent suppression of the genus Xerobiotus , which gathers macrobiotids with reduced claws. [ABSTRACT FROM AUTHOR]

The genus Barbaria , recently established to accommodate the former Echiniscus bigranulatus group, is a tardigrade group emblematic for the South American tardigrade fauna. This unappendaged echiniscid lineage is widely recognized for the so-called 'double' sculpturing composed of endocuticular pillars and pseudopores or pores in the dorsal cuticle. The phylogenetic relationships in the genus have so far been completely unknown, but the discovery of two new species (B. paucigranulata sp. nov. and B. weglarskae sp. nov.), together with new genetic data for further six species (B. bigranulata , B. charrua comb. nov. , B. danieli , B. jenningsi , B. madonnae and B. ollantaytamboensis), create an opportunity not only to uncover phyletic relationships, but also to reconstruct morphological evolution in the genus. To achieve this, we sequenced five genetic markers (18S rRNA, 28S rRNA, ITS1, ITS2, COI) for multiple populations of eight species of Barbaria (two-thirds of all known species) collected in Alabama (USA), Argentina and the Antarctic, and we analysed them in tandem with detailed morphological data. Our phylogentic analysis and the reconstruction of evolution of morphological traits suggests that the ancestor of the genus inhabited the Neotropics, and it was morphologically most similar to B. bigranulata. We also analyse literature records of Barbaria and conclude that the genus is most likely limited to the Neotropics, Antarctica and southern parts of the Nearctic. The findings are discussed in the context of the phylogeny of the Echiniscus evolutionary line. [ABSTRACT FROM AUTHOR]

There are two predominant sources of taxonomically useful morphological variability in the diverse tardigrade family Echiniscidae: the internal structure and surface sculpture of the cuticular plates covering the dorsum (sculpturing) and the arrangement and morphology of the trunk appendages (chaetotaxy). However, since the appendages often exhibit intraspecific variation (they can be reduced or can develop asymmetrically), sculpturing has been considered more stable at the species level and descriptions of new echiniscid species based solely on morphology are still being published. Here, we present a case study in which a detailed analysis of the morphology and multiple genetic markers of several species of the genus Viridiscus shows that cuticular sculpture may also exhibit considerable intraspecific variation and lead to false taxonomic conclusions. In a population collected from the eastern Nearctic, in the type locality of the recently described species V. miraviridis, individuals with transitional morphotypes between those reported for V. viridissimus and V. miraviridis were found. Importantly, all morphotypes within the viridissimus–miraviridis spectrum were grouped in a single monospecific clade according to rapidly evolving markers (ITS-1, ITS-2 and COI). Given the morphological and genetic evidence, we establish V. miraviridis as a junior synonym of V. viridissimus. This study explicitly demonstrates that a lack of DNA data associated with morphological descriptions of new taxa jeopardizes the efforts to unclutter tardigrade systematics. Additionally, V. perviridis and V. viridissimus are reported from Lâm Đồng Province in southern Vietnam, which considerably broadens their known geographic ranges. [ABSTRACT FROM AUTHOR]

One of the most extensive species radiations in the tardigrade evolution took place in the Echiniscus phylogenetic line, which contains the genus Echiniscus with over 120 species described to date. The internal classification of Echiniscus is historically based on two major sources of variability: chaetotaxy, that is the arrangement and the shape of trunk appendages, and the sculpturing of dorsal plates. These two criteria allowed for the delineation of species complexes, such as the blumi-canadensis or the spinulosus group. Recent phylogenetic analyses confirmed that they represent monophyletic lineages. However, the affinities of some species that have not been sequenced are not straightforward given their uncommon morphologies. In this paper, we present five Echiniscus species found in Argentina, two of which constitute such exemplary cases. Echiniscus aonikenk sp. nov. exhibits extraordinarily elongated cirri A , exceeding 50% of the body length, and dorsoventrally flattened trunk spines, including particularly wide spines E. The species is a probable sister group of the spinulosus complex. Furthermore, Echiniscus evelinae de Barros, 1942, reported here only third time ever, is characterised by an extreme elongation of cirri E , often exceeding the body length, and by autapomorphic dorsal sculpturing comprising epicuticular granules, pseudopores, distinct endocuticular reticulum and pillars. Analogously to E. aonikenk sp. nov. , E. evelinae apparently constitutes a separate evolutionary lineage. Finally, Echiniscus pellucidus sp. nov. (the merokensis complex), Echiniscus peruvianus Binda & Pilato, 1994 syn. nov. (the testudo complex) and Echiniscus manuelae da Cunha & do Nascimento Ribeiro, 1962 (the spinulosus complex) are analysed. Morphological peculiarities revealed in this study are discussed in the light of the Echiniscus taxonomy. [ABSTRACT FROM AUTHOR]

The taxonomy of many groups of meiofauna is challenging due to their low number of diagnostic morphological characters and their small body size. Therefore, with the advent of molecular techniques that provide a new source of traits, many cryptic species have started to be discovered. Tardigrades are not an exception, and many once thought to be cosmopolitan taxa are being found to be complexes of phenotypically similar species. Macrobiotus pallarii Maucci, 1954 was originally described in South Italy and has been subsequently recorded in Europe, America, and Asia. This allegedly wide geographic range suggests that multiple species may be hidden under this name. Moreover, recently, genetic evidence to support this was put forward, and the Macrobiotus pallarii complex has been proposed to accommodate putative species related to M. pallarii. Here, we describe three new pseudocryptic species based on populations that would have been all classified as Macrobiotus pallarii if molecular methods were not employed. Using an integrative taxonomy approach, we analyzed animals and eggs from the topotypic population of Macrobiotus pallarii, together with four other populations of the complex. We recovered four distinct phylogenetic lineages that, despite the overlap of morphometric traits, can be separated phenotypically by subtle but discrete morphological characters. One lineage corresponds to Macrobiotus pallarii, whereas the other three are newly described as Macrobiotus margoae Stec, Vecchi & Bartels, sp. nov. from the USA, Macrobiotus ripperi Stec, Vecchi & Michalczyk, sp. nov. from Poland and Finland, and Macrobiotus pseudopallarii Stec, Vecchi & Michalczyk, sp. nov. from Montenegro. To facilitate species identification, we provide a dichotomous key for species of the M. pallarii complex. Delimitation of these pseudocryptic taxa highlights the need for an integrative approach to uncover the phylum's diversity in full. [ABSTRACT FROM AUTHOR]

The family Richtersiidae, although established recently with the use of phylogenetic methods, was considered potentially paraphyletic at the time of its erection. Until now, the family comprised four genera, Richtersius, Diaforobiotus, Adorybiotus and a newly erected genus Crenubiotus. However, the genetic characterisation for the latter two genera was very limited or absent. To address concerns about the phylogenetic affinity of these two genera, we present a multilocus phylogeny of the families Richtersiidae and Murrayidae based on four molecular markers (18S rRNA, 28S rRNA, ITS-2 and COI). Our results show a distinct evolutionary lineage composed of Adorybiotus and Crenubiotus, which is sister to Murrayidae. In order to accommodate the phylogenetic and morphological distinctiveness of this lineage, we erect a new family, Adorybiotidae fam. nov. The new taxon differs morphologically from other families in the superfamily Macrobiotoidea by a unique combination of traits: (1) the presence of tubercles/cushions with aggregations of microgranules on their surfaces present on all legs and on the dorso-caudal cuticle, (2) a system of internal septa in claws, and (3) buccal apparatus morphology. Moreover, in order to stabilise the taxonomy and nomenclature in the genus Crenubiotus, we redescribe its type species, Crenubiotus crenulatus, by means of integrative taxonomy and designate a new neotype based on a population from the original terra typica. [ABSTRACT FROM AUTHOR]

[Display omitted] • Phylogenetic analysis recovered monophyly of the tardigrade genus Macrobiotus. • New evolutonaly distinct group is erected to the genus level (Sisubiotus gen. nov.) • The genus Xerobiotus is deeply nested within Macrobiotus and thus suppressed. • Distinct species complexes within Macrobiotus are delineated. • Demonstration of complex phenotypic evolution within the family Macrobiotidae. The family Macrobiotidae is one of the most speciose and diverse groups among tardigrades. Although there have been attempts to reconstruct the phylogeny of this family, the evolutionary relationships within Macrobiotidae are only superficially determined as available genetic data cover only a small fraction of this vast group. Here, we present the first extensive molecular phylogeny of the family based on four molecular markers (18S rRNA, 28Sr RNA, ITS-2 and COI) associated with detailed morphological data for the majority of taxa. The phylogenetic analysis includes nearly two hundred sequences representing more than sixty species, including sixteen taxa that have never been sequenced and/or analysed phylogenetically before. Our results recovered a new monophyletic group, comprising Macrobiotus spectabilis Thulin, 1928 and Macrobiotus grandis Richters, 1911, for which we erect a new genus, Sisubiotus gen. nov. , to accommodate its evolutionary distinctiveness. The largest, so far, dataset for the family Macrobiotidae showed that the genus Xerobiotus is nested within the clade representing the genus Macrobiotus deeper than it was earlier assumed, therefore we propose to suppress Xerobiotus and transfer its species to Macrobiotus. Moreover, mapping key morphological traits onto macrobiotid phylogeny exposed complex evolution of phenotypes within the Macrobiotus hufelandi group, i.e. Macrobiotus s.s. Finally, our findings enabled a detailed revision and discussion on species compositions of the most ubiquitous tardigrade genera, species groups and species complexes, which resulted in changes of taxonomic statuses of a number of macrobiotid species. All this contributes to the reconstruction of the morphological evolution within Macrobiotidae. [ABSTRACT FROM AUTHOR]