Revision of Testechiniscus Kristensen, 1987 (Heterotardigrada: Echiniscidae) refutes the polar-temperate distribution of the genus

Atlas of the Echiniscidae (Heterotardigrada) of the Worldpart I: West Palaearctic Echiniscus species

Traditionally Eurocentric tardigrade taxonomy has started to dissect endemics from very few truly cosmopolitan or widely distributed species, originally described mostly from the West Palaearctic, in the last decade. Obviously, the most problematic for taxonomic identification are species in large genera containing over 100 species in the case of Tardigrada. In limno-terrestrial heterotardigrades, only Echiniscus C.A.S. Schultze, 1840 fulfils this criterion, being a perfect example of taxonomic inflation. In Echiniscidae, this phenomenon results predominantly from the historical fallacy of attaching more importance to chaetotaxy than to the analysis of dorsal plate sculpturing. In this paper, the first of a series on echiniscids of the World, we review the current state of knowledge on the West Palaearctic Echiniscus species. Echiniscus granulatus (Doyre, 1840) and E. spinulosus (Doyre, 1840) are re-described based on multiple population data. Echiniscus lapponicus Thulin, 1911 and E. militaris Murray, 1911 are provided with the first SEM and molecular data, respectively. Following synonymies are made based on analyses of ample comparative material, type series, and redescriptions: E. blumi schizofilus Barto, 1941 syn. nov. and E. trojanus Maucci, 1973 syn. nov. of E. blumi blumi Richters, 1903; E. inocelatus Miheli, 1938 syn. nov., E. heterospinosus Maucci, 1954 syn. nov. and E. egnatiae Durante Pasa & Maucci, 1979 syn. nov. of E. granulatus; Echiniscus merokensis suecicus Thulin, 1911 syn. nov., E. columinis Murray, 1911 syn. nov., E. batramiae Iharos, 1936 syn. nov., E. jagodici Miheli, 1951 syn. nov. and E. laterospinosus Rudescu, 1964 syn. nov. of E. merokensis merokensis Richters, 1904; E. hexacanthus Maucci, 1973 syn. nov. of E. militaris Murray, 1911; E. carusoi Pilato, 1972 syn. nov. of E. spinulosus; E. osellai Maucci, 1974 syn. nov. of E. trisetosus Cunot, 1932. Two new nomina dubia are proposed: E. apuanus M. Bertolani, 1946 sp. dub. (and a probable synonymy with E. merokensis suggested) and E. pajstunensis Barto, 1941 sp. dub. Two new nomina inquirenda are established: E. marleyi Li, 2007 sp. inq. (another chaetotaxy-based morphotype of the Echiniscus blumi-canadensis complex) and E. punctus McInnes, 1995 sp. inq. (the lack of reliable morphological criteria separating it from E. granulatus). We summarise the morphological, phylogenetic and biogeographic information for the West Palaearctic Echiniscus species, and conclude with a total of 21 valid and identifiable taxa. We predict this number will decrease further with solving the species delimitation issues within the Echiniscus blumi-canadensis complex. Among these 21 taxa, 13 species (62%) are to be found solely in the Western Palaearctic and/or entire Holarctic regions. This augments the many recent findings that tardigrades are typically biogeographically structured and form clearly defined faunae.

Two new tardigrade genera from New Zealand's Southern Alp glaciers display morphological stasis and parallel evolution

Tardigrada is an invertebrate phylum that often constitutes a dominant micrometazoan group on glaciers worldwide. We investigated tardigrades residing in surface ice above the equilibrium line altitude (ELA) on three temperate glaciers of New Zealand's Southern Alps. Morphological, morphometric and multilocus DNA analyses (CO1, 18S rRNA, 28S rRNA, ITS-2) revealed two new genera comprising four species, of which two are formally described here: Kopakaius gen. nov. nicolae sp. nov. and Kararehius gen. nov. gregorii sp. nov. The former is represented by three genetically distinct phyletic lineages akin to species. According to CO1, Kopakaius gen. nov. nicolae sp. nov. inhabits Whataroa Glacier only while the remaining two Kopakaius species occur on Fox and Franz Joseph Glaciers, suggesting low dispersal capabilities. Although morphological characteristics of the new genera could indicate affinity with the subfamily Itaquasconinae, phylogenetic analysis placed them confidently in the subfamily Diphasconinae. Kopakaius gen. nov. lack placoids in the pharynx similar with some Itaquasconinae, whereas dark pigmentation and claw shape aligns them with the glacier-obligate genus, Cryobiotus (subfamily Hypsibiinae), which is an example of parallel evolution. The second genus, Kararehius gen nov. could be classified as Adropion-like (subfamily Itaquasconinae), but differs greatly by genetics (placed in the subfamily Diphasconinae) as well as morphology (e.g., lack of septulum), exemplify deep stasis in Hypsibiidae. Our results suggest that glacier fragmentation during the Pleistocene triggered tardigrade speciation, making it a suitable model for studies on allopatric divergence in glacier meiofauna.

A New Species of the GenusCrenubiotus (Tardigrada: Eutardigrada: Adorybiotidae) from Salt Spring Island, Strait of Georgia, British Columbia (Canada)

Currently, the recently erected genus Crenubiotus (Adorybiotidae, Macrobiotoidea) includes only three species, all of which are characterised by dentate lunulae and cuticular tubercules organised in the band in the dorso-caudal part of the body. By means of integrative taxonomy, we describe a fourth species of the genus: Crenubiotus salishani sp. nov., from Salt Spring Island in British Columbia, Canada. The new species has been found in the moss growing on rock and differs from the other species in the genus due to the presence of a median anterior mucrone in the third band of the oral cavity armature (OCA) and by the presence of evident thickenings on the eggshell connecting the neighbouring processes. This finding highlights the importance of continuing to study tardigrade biodiversity, even in already explored areas, and how an integrative approach is fundamental to achieving a reliable measure of biodiversity.

Diversification rates in Tardigrada indicate a decreasing tempo of lineage splitting regardless of reproductive mode

Understanding the dynamics of speciation and extinction events is one of the most interesting subjects in evolutionary biology that relates to all life forms, even the smallest ones. Tardigrades are microscopic invertebrates that attracted public and scientific attention mostly due to their ability to enter into the diapause stage called cryptobiosis and in such stage resist extremely harsh environmental conditions. However, although recent research solved a considerable number of phylogenetic uncertainties and further uncovered physiological mechanisms of cryptobiosis, not much attention is given to the evolutionary forces shaping tardigrade diversity. Here, we investigated the effect of reproductive mode on diversification rates in tardigrades using three groups: macrobiotids, echiniscids and milnesids, which represent low, moderate and high levels of parthenogenesis, respectively. Our results showed a decreasing tempo of diversification events for each of the studied groups without any differences that could be ascribed to reproductive mode. We discussed the observed lack of effect in tardigrades acknowledging deficiencies in available data sets and encouraging further studies to understand whether our results can be considered reliable.

Rough backs: taxonomic value of epicuticular sculpturing in the genus Milnesium Doyère, 1840 (Tardigrada: Apochela)

The phylum Tardigrada comprises ~ 1400 described species that inhabit a wide range of ecosystems throughout the globe. Tardigrades are generally considered taxonomically challenging due to a strongly limited number of taxonomically informative morphological traits and microscopic size. Of all tardigrade groups, the taxonomy of Milnesium Doyère, 1840 is particularly difficult because in comparison with most other eutardigrades, the genus lacks the taxonomically informative egg shell ornamentation and/or placoids in the muscle pharynx. Therefore, any new morphological traits that could be used in species delineation and identification are priceless. In this contribution, we review and evaluate taxonomic value of the dorsal cuticle morphology. Specifically, by means of experimental taxonomy, we demonstrate the first extreme case of ontogenetic variability in dorsal epicuticle sculpturing using a new species from Portugal, Milnesium decorumsp. nov. Furthermore, we verify the existence of dorsal gibbosities in Milnesium reticulatum Pilato, Binda, Lisi, 2002, the only species of the genus allegedly exhibiting these structures. Finally, we provide a diagnostic key to the Milnesium granulatum morphogroup.

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.

The Macrobiotus ariekammensis species complex provides evidence for parallel evolution of claw elongation in macrobiotid tardigrades

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.

Molecular Phylogenetics, Speciation, and Long Distance Dispersal in Tardigrade Evolution: A case study of the genusMilnesium

Microorganisms (sensu lato, i.e., including micrometazoans) are thought to have cosmopolitan geographic distributions due to their theoretically unlimited dispersal capabilities, a consequence of their tiny size, population dynamics, and resistant forms. However, several molecular studies of microorganisms have identified biogeographic patterns indicating cryptic speciation and/or weak species definitions. Using a multi-locus approach with the genus Milnesium (Tardigrada), we aimed to determine the genetic structure of populations worldwide and the effects of long distance dispersal (LDD) on genetic connectivity and relationships across the six continents. Our results on this micrometazoan's genetic structure and LDD at global and micro-local scales indicate contrasting patterns not easily explained by a unique or simple phenomenon. Overall, we report three key findings: (i) confirmation of long distance dispersal for tardigrades, (ii) populations with globally-shared or endemic micro-local haplotypes, and (iii) a supported genetic structure instead of the homogeneous genetic distribution hypothesized for microorganisms with LDD capabilities. Moreover, incongruences between our morphological and molecular results suggest that species delimitation within the genus Milnesium could be problematic due to homoplasy. Duality found for Milnesium populations at the global scale, namely, a molecular phylogenetic structure mixed with widely distributed haplotypes (but without any apparent biogeographic structure), is similar to patterns observed for some unicellular, prokaryotic and eukaryotic, microorganisms. Factors influencing these patterns are discussed within an evolutionary framework.

"Everything is not everywhere": Time-calibrated phylogeography of the genus Milnesium (Tardigrada)

There is ample evidence that macroscopic animals form geographic clusters termed as zoogeographic realms, whereas distributions of species of microscopic animals are still poorly understood. The common view has been that micrometazoans, thanks to their putatively excellent dispersal abilities, are subject to the "Everything is everywhere but environment selects" hypothesis (EiE). One of such groups, <1 mm in length, are limnoterrestrial water bears (Tardigrada), which can additionally enter cryptobiosis that should further enhance their potential for long distance dispersion (e.g., by wind). However, an increasing number of studies, including the most recent phylogeny of the eutardigrade genus Milnesium, seem to question the general applicability of the EiE hypothesis to tardigrade species. Nevertheless, all Milnesium phylogenies published to date were based on a limited number of populations, which are likely to falsely suggest limited geographic ranges. Thus, in order to test the EiE hypothesis more confidently, we considerably enlarged the Milnesium data set both taxonomically and geographically, and analysed it in tandem with climate type and reproductive mode. Additionally, we time-calibrated our phylogeny to align it with major geological events. Our results show that, although cases of long distance dispersal are present, they seem to be rare and mostly ancient. Overall, Milnesium species are restricted to single zoogeographic realms, which suggests that these tardigrades have limited dispersal abilities. Finally, our results also suggest that the breakdown of Gondwana may have influenced the evolutionary history of Milnesium. In conclusion, phylogenetic relationships within the genus seem to be determined mainly by paleogeography.

Integrative taxonomy resolves species identities within the Macrobiotus pallarii complex (Eutardigrada: Macrobiotidae)

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.

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 &amp; 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 &amp; Bertolani, 2004, Macrobiotus noemiae Roszkowska &amp; Kaczmarek, 2019, Macrobiotus santoroi Pilato &amp; D’Urso, 1976, and Macrobiotus serratus Bertolani, Guidi &amp; 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.

Echiniscidae in the Mascarenes: the wonders of Mauritius

Many regions of the world remain unexplored in terms of the tardigrade diversity, and the islands of the Indian Ocean are no exception. In this work, we report four species of the family Echiniscidae representing three genera from Mauritius, the second largest island in the Mascarene Archipelago. Two species belong in the genus Echiniscus: Echiniscus perarmatus Murray, 1907, a pantropical species, and one new species: Echiniscus insularissp. nov., one of the smallest members of the spinulosus group and the entire genus, being particularly interesting due to the presence of males and supernumerary teeth-like spicules along the margins of the dorsal plates. The new species most closely resembles Echiniscus tropicalis Binda &amp; Pilato, 1995, for which we present extensive multipopulation data and greatly extend its distribution eastwards towards islands of Southeast Asia. Pseudechiniscus (Meridioniscus) mascarenensissp. nov. is a typical member of the subgenus with elongated (dactyloid) cephalic papillae and the pseudosegmental plate IV’ with reduced posterior projections in males. Finally, a Bryodelphax specimen is also recorded. The assemblage of both presumably endemic and widely distributed tardigrade species in Mauritius fits the recent emerging biogeographic patterns for this group of micrometazoans.

New Asian and Nearctic Hypechiniscus species (Heterotardigrada: Echiniscidae) signalize a pseudocryptic horn of plenty

The cosmopolitan echiniscid genus Hypechiniscus contains exclusively rare species. In this contribution, by combining statistical morphometry and molecular phylogeny, we present qualitative and quantitative aspects of Hypechiniscus diversity, which remained hidden under the two purportedly cosmopolitan species: H. gladiator and H. exarmatus. A neotype is designated for H. gladiator from Creag Meagaidh (Scotland), and an informal re-description is provided for H. exarmatus based on animals from Creag Meagaidh and the Isle of Skye (Inner Hebrides). Subspecies/forms of H. gladiator are suppressed due to the high developmental variability of the cirrus dorsalis. At the same time, four species of the genus are described: H. daedalus sp. nov. from Roan Mountain and the Great Smoky Mountains (Southern Appalachian Mountains, USA), H. flavus sp. nov. and H. geminus sp. nov. from the Yatsugatake Mountains (Honshu, Japan), and H. cataractus sp. nov. from the Malay Archipelago (Borneo and the Moluccas). Dorsal and ventral sculpturing, together with morphometric traits, are shown to be the key characters that allow for the phenotypic discrimination of species within the genus. Furthermore, the morphology of Hypechiniscus is discussed and compared to that of the most similar genera, Pseudechiniscus and Stellariscus. Finally, a diagnostic key to all recognized Hypechiniscus species is provided.

Resolving the systematics of Richtersiidae by multilocus phylogeny and an integrative redescription of the nominal species for the genus Crenubiotus (Tardigrada)

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.

New multilocus phylogeny reorganises the family Macrobiotidae (Eutardigrada) and unveils complex morphological evolution of the Macrobiotus hufelandi group

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, Sisubiotusgen. 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.

Pseudechiniscus in Japan: re-description of Pseudechiniscus asper Abe et al., 1998 and description of Pseudechiniscus shintai sp. nov

The classification and identification of species within the genus Pseudechiniscus Thulin, 1911 has been considered almost a Sisyphean work due to an extremely high homogeneity of its members. Only recently have several contributions made progress in the taxonomy feasible through their detailed analyses of morphology and, crucially, by the re-description of the ancient, nominal species P. suillus (Ehrenberg, 1853). Herein, we focus on the Japanese representatives of this genus: P. asper, a rare species originally described from Hokkaido, and a new species P. shintai. Both taxa belong to the widespread suillus-facettalis complex. Detailed descriptions entailing DNA barcoding of four markers and illustrations of the ventral pillar patterns are indispensable for an accurate delineation of species within this genus.

Integrative Descriptions of Two New Macrobiotidae Species (Tardigrada: Eutardigrada: Macrobiotoidea) from French Guiana and Malaysian Borneo

In this paper we describe two new tardigrade species, one representing the Macrobiotus hufelandi complex and the other from the Paramacrobiotus richtersi complex. The descriptions are based on a detailed morphological examination under light and scanning electron microscopy and analysis of four genetic markers (18S rRNA, 28S rRNA, ITS-2 and COI). Macrobiotus crustulus sp. nov. from French Guiana is the most similar to Macrobiotus martini Bartels, Pilato, Lisi and Nelson, 2009, Macrobiotus santoroi Pilato and D'Urso, 1976, but differs from them mainly by having the lissostomus type of the oral cavity armature (teeth not visible under light microscopy) and well-developed, convex terminal discs of egg processes covered with evident granulation. Paramacrobiotus filipi sp. nov. from the Malaysian part of Borneo is the most similar to Paramacrobiotus alekseevi (Tumanov, 2005), but differs from it primarily by the presence of body granulation visible under light microscopy as well as sculptured and porous areoles around egg processes.

Revised Cornechiniscus (Heterotardigrada) and new phylogenetic analyses negate echiniscid subfamilies and tribes

Echiniscidae are undoubtedly the most thoroughly studied lineage of the class Heterotardigrada. Recently, new subfamilies and tribes grouping echiniscid genera based on traditionally recognized morphological clues have been proposed. Here, by integrative analyses of morphology and DNA sequences of numerous populations of a rare genus Cornechiniscus, we show that this hypothesized classification is artificial. Specifically, we demonstrate that Echiniscinae are diphyletic, as Bryodelphax forms a distinct phyletic lineage within Echiniscidae, and Pseudechiniscinae are polyphyletic, with Mopsechiniscus being indirectly related to Pseudechiniscus, which is closer to the Echiniscus-like genera than to other genera with pseudosegmental plates. Consequently, the subfamilies and tribes are considered as unsupported from the phylogenetic and morphological point of view. The genus Cornechiniscus is revised, and the phenotypic diagnoses of several species are updated thanks to new rich material from Africa, Asia and Europe. Cornechiniscus imperfectus sp. nov. is described from mountains of Kyrgyzstan, being the second appendaged species within the genus and the third known to exhibit dioecy. A taxonomic key to the genus is provided. Systematic positions of Acanthechiniscus and Multipseudechiniscus are also discussed. Acanthechiniscus goedeni is confirmed to be a member of the genus Acanthechiniscus.

Small is beautiful: the first phylogenetic analysis of Bryodelphax Thulin, 1928 (Heterotardigrada, Echiniscidae)

The phyletic relationships both between and within many of tardigrade genera have been barely studied and they remain obscure. Amongst them is the cosmopolitan Bryodelphax, one of the smallest in terms of body size echiniscid genera. The analysis of newly-found populations and species from the Mediterranean region and from South-East Asia gave us an opportunity to present the first phylogeny of this genus, which showed that phenotypic traits used in classical Bryodelphax taxonomy do not correlate with their phyletic relationships. In contrast, geographic distribution of the analysed species suggests their limited dispersal abilities and seems to be a reliable predictor of phylogenetic affinities within the genus. Moreover, we describe three new species of the genus. Bryodelphax australasiaticussp. nov., by having the ventral plate configuration VII:4-4-2-4-2-2-1, is a new member of the weglarskae group with a wide geographic range extending from the Malay Peninsula through the Malay Archipelago to Australia. Bryodelphax decoratussp. nov. from Central Sulawesi (Celebes) also belongs to the weglarskae group (poorly visible ventral plates VII:4-2-2-4-2-2-1) and is closely related to the recently described Bryodelphax arenosus Gąsiorek, 2018, but is differentiated from the latter by well-developed epicuticular granules on the dorsum. Finally, a new dioecious species, Bryodelphax nigripunctatussp. nov., is described from Mallorca and, by the reduced ventral armature (II/III:2-2-(1)), it resembles Bryodelphax maculatus Gąsiorek et al., 2017. The latter species, known so far only from northern Africa, is recorded from Europe for the first time. A taxonomic key to the genus members is also presented.

An overview of the sexual dimorphism in Echiniscus (Heterotardigrada, Echiniscoidea), with the description of Echiniscus masculinus sp. nov. (the virginicus complex) from Borneo

Members of the genus Echiniscus C.A.S. Schultze, 1840 are mostly unisexual, with thelytokously reproducing females. Therefore, every newly described dioecious species in the genus is particularly interesting. Here, we describe Echiniscus masculinussp. nov. from Gunung Kinabalu, the highest peak of Borneo and the entire Southeast Asia. The new species belongs in the predominantly parthenogenetic E. virginicus complex, and its females are confusingly similar to females of the pantropical E. lineatus Pilato et al., 2008, another member of this group. However, genetic evidence and noticeable sexual dimorphism clearly delineate the new species. Males of E. masculinussp. nov. are unlike females in the body proportions, cuticular sculpturing, and appendage configuration. The new discoveries provide a justification to review the current knowledge about evolution and forms of sexual dimorphism within Echiniscus.

High diversity in the Pseudechiniscus suillus–facettalis complex (Heterotardigrada: Echiniscidae) with remarks on the morphology of the genus Pseudechiniscus

Pseudechiniscus is a morphologically homogeneous genus of tardigrades. The morphological features commonly used for species discrimination in this genus are the dorsal sculpture, the shape and number of dorsal plates and trunk appendages. Species of the Pseudechiniscus suillus–facettalis complex are one of the most challenging tardigrades to identify. All species are similar in their general appearance and all lack trunk appendages. Moreover, not only the nominal Pseudechiniscus suillus, but also other members of the suillus–facettalis complex have been insufficiently described. In our study, we examined several populations from the Northern and the Southern Hemispheres that could be traditionally attributed to Pse. suillus. These populations were analysed using integrative taxonomy – a combination of classical morphology and morphometry with molecular data. Besides the differences in the dorsal sculpture and morphometry, we also found species-specific differences in ventral sculpture, which were originally used for discrimination of Pseudechiniscus species. Moreover, we provide an extensive discussion on all morphological and morphometric differences used in Pseudechiniscus taxonomy and indicate main taxonomic problems with this genus. Finally, we redescribe the nominal Pse. suillus from Italy.

A new redescription of Richtersius coronifer, supported by transcriptome, provides resources for describing concealed species diversity within the monotypic genus Richtersius (Eutardigrada)

Richtersius coronifer, the nominal species for the family Richtersiidae and a popular laboratory model, exemplifies a common problem in modern tardigrade taxonomy. Despite undeniable progress in the field, many old and incomplete descriptions of taxa hinder both species delimitation and the estimation of species diversity and distribution. Although for over a century this species has been recorded throughout the world, recent research indicates that records to date are likely to represent a species complex rather than a single cosmopolitan species. However, in order to recognise and name species diversity within the complex, an integrative redescription of the nominal species is first needed. Here, we describe an R. coronifer population collected from Spitsbergen, i.e., one of the two localities mentioned in the original description, with detailed morphological and morphometric data associated with standard DNA sequences of four standard genetic markers (18S rRNA, 28S rRNA, ITS-2, and COI) and supported by transcriptome sequencing. We propose replacement of the neotype designated in 1981 by Maucci and Ramazzotti, as it is impossible to verify whether the existing neotype is conspecific with specimens studied by Richters in 1903 and 1904. Finally, using newly obtained cytochrome c oxidase subunit I (COI) sequences of populations from Spitsbergen, Italy, Poland, and Greece together with sequences deposited in GenBank (China, Greenland, Italy, Mongolia), we performed genetic species delimitation, which indicated seven distinct potential species within the genus Richtersius, in addition to the nominal taxon. This study marks a starting point for further research on the taxonomy of and species diversity within the genus. Moreover, this work has the potential to be the first tardigrade redescription to provide both genetic barcodes and a transcriptome of the species in question.

Untangling systematics of the Paramacrobiotus areolatus species complex by an integrative redescription of the nominal species for the group, with multilocus phylogeny and species delineation in the genus Paramacrobiotus

Incomplete descriptions of nominal taxa are one of the most significant obstacles in modern taxonomy, including the taxonomy of Tardigrada. Another major problem in tardigrade systematics is the lack of tests for the reliability of genetic markers in species delineation. Here, we employ an integrative taxonomy approach to redescribe the nominal taxon for the P. areolatus complex, Paramacrobiotus areolatus. Moreover, we obtained multilocus DNA sequences for another 16 populations representing 9–12 Paramacrobiotus species collected from Europe, North America, Africa and Australia, enabling us to reconstruct the most extensive phylogeny of the genus to date. The identification of a pair of potentially cryptic dioecious P. areolatus complex species with divergent genetic distances in ITS2 (1.4%) and COI (13.8%) provided an opportunity to test the biological species concept for the first time in the history of tardigrade taxonomy. Intra- and interpopulation crosses did not differ in reproductive success in terms of F1 offspring. However, because of the low F1 family sizes, we were unfortunately unable to test F1 hybrid fertility. Although our results are only partially conclusive, they offer a baseline not only for further taxonomic and phylogenetic research on the areolatus complex, but also for studies on species delineation in tardigrades in general.

What If Multiple Claw Configurations Are Present in A Sample? A Case Study with the Description of Milnesium pseudotardigradum sp. nov. (Tardigrada) with Unique Developmental Variability

The tardigrade fauna of Iceland has been a subject of studies since mid XX century. So far, only a single species of the genus Milnesium has been reported from the island, M. tardigradum, which at the time was assumed to have a cosmopolitan distribution. However, the record comes from before the redescription of M. tardigradum, thus the validity of the Icelandic report is questionable. Some species of Milnesium are characterised by developmental variability, which is most pronounced in the morphology of secondary branches of claws, exhibited by shifts in the number of spurs. In this contribution, we present a case study in which multiple claw configurations (CC) were found in a single lichen sample from Iceland, indicating the presence of more than one species and/or ontogenetic variability. To elucidate this puzzle, we utilised a range of integrative tools, including detailed morphology, morphometry, barcoding and development tracking. We present the workflow, which enabled us to collect the data for each species/morphotype. In result, we revealed the presence of three species, two characterised by ontogenetic CC change (M. variefidum and a new species) and one with a stable CC (a new species). Here, we describe one of these new species, M. pseudotardigradum, which is extremely similar to M. tardigradum, but can be phenotypically differentiated by a unique, double CC change pattern.

An integrated study of the biodiversity within the Pseudechiniscus suillus–facettalis group (Heterotardigrada: Echiniscidae)

Pseudechiniscus is the second most species-rich genus in Heterotardigrada and in the family Echiniscidae. However, previous studies have pointed out polyphyly and heterogeneity in this taxon. The recent erection of the genus Acanthechiniscus was another step in making Pseudechiniscus monophyletic, but species identification is still problematic. The present investigation aims at clarifying biodiversity and taxonomy of Pseudechiniscus taxa, with a special focus on species pertaining to the so-called ‘suillus–facettalis group’, by using an integrated approach of morphological and molecular investigations. The analysis of sequences from specimens sampled in Europe and Asia confirms the monophyly of the genus Pseudechiniscus. Inside the genus, two main evolutionary lineages are recognizable: the P. novaezeelandiae lineage and the P. suillus–facettalis group lineage. Inside the P. suillus–facettalis group, COI molecular data points out a very high variability between sampled localities, but in some cases also among specimens sampled in the same locality (up to 33.3% p-distance). The integrated approach to the study of Pseudechiniscus allows confirmation of its monophyly and highlights the relationships in the taxon, pointing to its global distribution.

New Echiniscidae (Heterotardigrada) from Amber Mountain (Northern Madagascar)

A moss sample from the local biodiversity hotspot in lowland rainforest in the vicinity of Amber Mountain, Madagascar, yielded the discovery of twoEchiniscusC.A.S. Schultze, 1840 species, of which one is new to science.Echiniscussuccineussp. nov.is related to other members of thespinulosusgroup, but differs from them by the highly complicated structure of the dorsal plates, with intricately thickened parts of the armour forming ornamented pattern. The validity of the intraporal dark rings as a taxonomic trait is discussed in the context of the recovered intraspecific variability for the new taxon. Besides, rareEchiniscusafricanusMurray, 1907 is reported for the first time from the island.