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.

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.

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 & 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.

Multi-marker DNA metabarcoding reflects tardigrade diversity in different habitats

Like meiofauna in general, tardigrades are often neglected in ecological and environmental surveys. Tardigrades occur in all parts of the world, from deep marine sediments to alpine environments, and are present in most ecosystems. They are therefore potentially good candidates for biomonitoring programs. However, sampling of these minute animals is both tedious and time-consuming, impeding their inclusion in large-scale ecological surveys. In this study we argue that using a multi-marker metabarcoding approach on environmental DNA (eDNA) partly can overcome this barrier. Samples of moss, lichens, and leaf litter were investigated both by morphology-based methods and DNA metabarcoding, and the results were compared in terms of tardigrade diversity and community composition of the sampled microhabitats. DNA metabarcoding using three markers detected more species of tardigrades than identification by morphology in most samples. Also, metabarcoding detected the same community differences and microhabitat distribution patterns as morphology-based methods. In general, metabarcoding of litter samples was unreliable, with only one out of three markers consistently amplifying and detecting tardigrades. The low availability of tardigrade reference sequences in public databases restricts the taxonomic resolution in eDNA surveys, but this impediment is partly circumvented by utilizing multiple markers.

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.

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.

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.

Analysis of non-morphometric morphological characters used in the taxonomy of the genus Pseudechiniscus (Tardigrada: Echiniscidae)

Pseudechiniscus, the second-largest genus of the family Echiniscidae (Tardigrada: Heterotardigrada: Echiniscoidea), is notoriously difficult for taxonomic studies. In this study, I performed a morphological analysis of a new species from Croatia, based on a light microscopic and scanning electron microscopic examination of 45 specimens from the same sample. Furthermore, I have summarized all available data on Pseudechiniscus species, including their original descriptions, and have analysed the following complexes of morphological characters: (1) arrangement and morphology of dorsal cuticular plates, (2) ventral sculpture, (3) morphology of cephalic, trunk and leg sensory organs and (4) claw morphology. The applicability of these characters in the taxonomy and their distribution in the genus are discussed. Some of the characters traditionally used for species delimitation were shown to be unsuitable and others in need of a thorough reinvestigation. The meaning of the old term ‘faceted’, commonly used but often misapplied, has been clarified, based on the initial definition. Several characters of the claw structure were suggested as potentially useful for species delimitation. The taxonomic status of several old forms and species was discussed.