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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]

Ranges of tardigrade intraspecific and interspecific variability are not precisely defined, both in terms of morphology and genetics, rendering descriptions of new taxa a cumbersome task. This contribution enhances the morphological and molecular dataset available for the heterotardigrade genus Viridiscus by supplying new information on Southern Nearctic populations of V.perviridis, V.viridianus, and a new species from Tennessee. We demonstrate that, putting aside already well-documented cases of significant variability in chaetotaxy, the dorsal plate sculpturing and other useful diagnostic characters, such as morphology of clavae and pedal platelets, may also be more phenotypically plastic characters at the species level than previously assumed. As a result of our integrative analyses, V.viridianus is redescribed, V.celatus sp. nov. described, and V.clavispinosus designated as nomeninquirendum, and its junior synonymy with regard to V.viridianus suggested. Morphs of three Viridiscus species (V.perviridis, V.viridianus, and V.viridissimus) are depicted, and the implications for general echiniscid taxonomy are drawn. We emphasise that taxonomic conclusions reached solely through morphological or molecular analyses lead to a distorted view on tardigrade α-diversity. [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 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. [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 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. [ABSTRACT FROM AUTHOR]

Recent years have brought undeniable progress in tardigrade taxonomy, and speciose complexes were detected in a number of phylogenetic lineages. The family Echiniscidae is one such lineage; it is one of the most diverse groups of limno-terrestrial tardigrades and can be characterized as having achieved great evolutionary success. In this contribution, using populations representing several species that originated from the Indomalayan region, we reconstructed phylogenetic affinities within Nebularmis, a recently erected genus within the Echiniscus lineage. Nebularmis auratussp. nov. and Nebularmis burmensissp. nov. are described from the Eastern Yoma Mountains and the Shan Hills (Myanmar), Nebularmis bhutanensissp. nov. is described from the Eastern Himalayas (Bhutan), and Nebularmis indicussp. nov. is described from the foothills of the Western Ghats (Goa, India). Moreover, males are reported in populations of the last two species. All known members of the genus can be phenotypically differentiated based on minute details of their dorsal sculpture and claws. Moreover, a very wide tropical distribution is demonstrated for Nebularmis cirinoi, recorded for the first time from islands of the Malay Archipelago. Furthemore, novel morphological, genetic, and geographic data allowed for the clarification of the generic diagnosis. Currently available data favor a scenario under which Nebularmis evolved in Southeast Asia and later dispersed to other regions of the globe. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Identification of tardigrade species is still reliant mostly on morphological and morphometric traits. Given that the number of taxonomically significant traits available in the genus Milnesium is exceptionally low, ontogenetic variability may provide additional methods for species delineation. However, it is notoriously difficult to establish whether both immature and sexually mature instars are present in examined populations. Here, we developed a simple analytical morphometric method that helps in testing whether both immature and mature life stages are present in a given set of individuals. In order to achieve this, we analysed 21 populations representing 11 Milnesium species, with developmental tracking data available for four species. Using cluster analysis, individuals were assigned accurately to three groups of instars: hatchlings, juveniles and adults (third instar onwards). Our analyses revealed that the most useful character in life-stage classification is buccal tube length. The method of classification of instars presented herein could be used as a simple tool for identification of the number of life stages present in a population. Finally, using our algorithm, we analysed morphometric datasets underlying the descriptions and redescriptions of all known Milnesium species to date and concluded that the majority of them did not include all three life-stage groups. [ABSTRACT FROM AUTHOR]

In this study, a new species of the Mesobiotus furciger group from Diliman, Quezon City, Philippines was identified using an integrative taxonomy approach. Morphological and morphometric data obtained through phase and Nomarski contrast microscopy and scanning electron microscopy along with molecular analyses of the DNA sequences of four molecular markers (18S rRNA, 28S rRNA, ITS-2, and COI) support the erection of Mesobiotus dilimanensis, new species. The new species is the third limno-terrestrial tardigrade species from the Philippines described as new to science and is the first member of the Mesobiotus furciger species complex described using an integrative taxonomy approach in the country. [ABSTRACT FROM AUTHOR]

Outdated and inaccurate original descriptions of species nominal for genera or species complexes give birth to notorious difficulties in species identification and often translate into erroneous classifications of multiple species as one. This, in turn, results in severe overestimations of specific geographic ranges and ultimately in underestimations of the diversity of organisms living on our planet. Tardigrades, ubiquitous microscopic metazoans exhibiting relatively few taxonomically useful traits, bear many such problematic species. In this paper, we investigated, morphologically and molecularly, 10 European populations of Ramazzottius cf. oberhaeuseri (Doyère, 1840), a putatively cosmopolitan nominal species for the family Ramazzottiidae. The analysis of COI sequences revealed eight potential species, including one from Paris, the type locality of R. oberhaeuseri, which we used to integratively redescribe the nominal taxon. The identification of seven further species in a handful of samples collected from a single continent explicitly shows the considerable undescribed species diversity within this group and puts in question the cosmopolitan distribution of R. oberhaeuseri. The integrative redescription of R. oberhaeuseri opens the opportunity for descriptions of other species in the complex. http://zoobank.org/urn:lsid:zoobank.org:pub:50B99B53-C317-4DBD-8CF1-16297B85C4F3 [ABSTRACT FROM AUTHOR]

Tardigrades are ubiquitous microfauna that act as consumers and predators in soil food webs. Several studies have suggested that tardigrades have great potential to control nematode populations. However, the regulatory function of tardigrades depends on many factors, including their feeding preferences. Yet, tardigrade feeding preferences remain largely unresolved. Therefore, in our experiment, nine predatory tardigrade species were tested for their preferences for three types of microfauna prey (nematodes, rotifers and tardigrades) under controlled laboratory conditions. We also tested whether tardigrade prey preferences can be predicted by selected functional traits (body length and buccal tube dimensions), because such traits are known to be a powerful tool in determining ecological links between organisms. We observed overall avoidance of tardigrades as prey along with preference for nematode prey. The difference in the total consumed number of the three types of prey were attributable to predator species identity, whereas proportional differences in the three types of prey in the diet were attributable to buccal tube length. Buccal tube width, buccal tube width to length ratio and body length lacked the predictive power for feeding preferences of predatory tardigrades. Our results showed that buccal tube length is more informative of tardigrade prey preference than predator species identity and can be used to predict tardigrade feeding preferences. The knowledge of tardigrade feeding preferences is crucial for understanding the role of tardigrades in soil food web. • Prey preference of predatory tardigrades can be estimated by buccal tube length. • The longer the buccal tube, the higher proportion of tardigrades in the diet. • The longer the buccal tube, the lower proportion of nematodes in the diet. [ABSTRACT FROM AUTHOR]