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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.

Marine tidal heterotardigrades (Echiniscoididae) have gained increasing interest owing to their unique adaptations and evolutionary position, bridging marine and limnoterrestrial taxa. Echiniscoididae was established to accommodate the marine genera Anisonyches and Echiniscoides. However, it has become apparent that Anisonyches, with its claw configuration, median cirrus and seminal receptacles, clearly has little or no affinity to tidal echiniscoidids with supernumerary claws. Consequently, we establish Anisonychidae fam. nov. to accommodate Anisonyches in a paraphyletic Arthrotardigrada and discuss its affinity to other heterotardigrade taxa. We recently split Echiniscoides into Isoechiniscoides and Echiniscoides s.l. The latter remains a miscellany of species complexes and undescribed genera, and it has become evident that a larger number of echiniscoidids belonging to Echiniscoides, Isoechiniscoides and undescribed genera coexist in intertidal sediments. Here, we erect Neoechiniscoides aski gen. nov., sp. nov. from Roscoff, France, which has a unique anal system, characterized by prominent lateral lobes with a set of wing-like structures. Phylogenetic analyses based on COI sequences infer a close relationship between N. aski, an undescribed species from Roscoff and unidentified species from Maine, USA. We propose that the new genus includes the former Echiniscoides species Echiniscoides pollocki and Echiniscoides horningi, which we hereby transfer.

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.

A large number of specimens (1563) of a new Florarctus species were collected in a single intertidal sample from the Ionian Sea, Italy. The postembryonic development of the new species was studied with emphasis on external morphology and functional anatomy. The new Florarctus species was recognized as having two distinct larval stages, during which the anus is formed and the gonads mature prior to the development of a gonopore. The larval stages are followed by one adult stage in females and two adult stages in males. Cuticular structures change in morphology during postembryonic development, so that they exhibit a juvenile and an adult appearance. The accelerated growth in gonadal development could be the result of paedomorphosis, which was observed in the tendency of adult males of the new Florarctus species to maintain juvenile character conditions.

Although morphological characters distinguishing echiniscid genera and species are well understood, the phylogenetic relationships of these taxa are not well established. We thus investigated the phylogeny of Echiniscidae, assessed the monophyly of Echiniscus, and explored the value of cuticular ornamentation as a phylogenetic character within Echiniscus. To do this, DNA was extracted from single individuals for multiple Echiniscus species, and 18S and 28S rRNA gene fragments were sequenced. Each specimen was photographed, and published in an open database prior to DNA extraction, to make morphological evidence available for future inquiries. An updated phylogeny of the class Heterotardigrada is provided, and conflict between the obtained molecular trees and the distribution of dorsal plates among echiniscid genera is highlighted. The monophyly of Echiniscus was corroborated by the data, with the recent genus Diploechiniscus inferred as its sister group, and Testechiniscus as the sister group of this assemblage. Three groups that closely correspond to specific types of cuticular design in Echiniscus have been found with a parsimony network constructed with 18S rRNA data. © 2013 The Linnean Society of London

Although studies describing molecular-based phylogenies within tardigrades are now frequently being published, this is not the case for studies combining molecular and morphological characters. Tardigrade phylogeny is still based, from a morphological point of view, almost exclusively on chitinous structures and little attention has been given to detecting and using novel morphological data. Consequently, we analysed the musculature of seven tardigrade species belonging to the main phyletic lines by confocal laser scanning microscopy and compared these morphological results with new molecular analyses (18S+28S rRNA genes). Finally, we analysed all the data with a total evidence approach. A consilience in the phylogenetic relationships among orders and superfamilies of tardigrades was obtained among the evolutionary trees obtained from morphological, molecular and total evidence approaches. Comparative analysis on the musculature allowed the identification of serial homologies and repeated metameric patterns along the longitudinal animal body axis. A phenomenon of mosaic evolution was detected in musculature anatomy, as dorsal musculature was found to be highly modified with respect to the other body muscle groups, probably related to the evolution of dorsal cuticular plates. An understanding of tardigrade musculature anatomy will give fundamental information to understand the evolution of segmental pattern within Panarthropoda. © 2013 The Linnean Society of London

Tardigrades were collected from three seepage spring sites at 549 m on Short Mountain, Cannon County, Tennessee. Three terrestrial samples and three aquatic samples were taken monthly from each site. Terrestrial samples included mosses and lichens from rocks and fallen trees; one sample of leaf litter was also collected from two of the sites. Aquatic samples included sediment, decaying leaf litter, and aquatic plants. Specimens of tardigrades were mounted on individual slides in Hoyer's medium. Species were identified and photographed using phase and differential contrast microscopy. Twenty-eight species representing 13 genera were recorded: Pseudechiniscus, Echiniscus, Doryphoribius, Ramazzottius, Hypsibius, Isohypsibius, Diphascon, Platicrista, Itaquascon, Murrayon, Macrobiotus, Minibiotus , and Milnesium . One of the Pseudechiniscus species and an Isohypsibius species were new to science and are described in this paper.

The brain of Echiniscus viridissimus , Peterfi, 1956 is composed of a series of orthogonally arranged neuropils. The most anterior neuropils are circumbuccal, positioned dorso- and ventrolateral to the buccal tube and are associated with ganglia for sensory receptors of the mouth cone. Posterior to these are neuropils and ganglia for the (1) internal cirri and (2) cephalic papillae, external cirri, cirri A and clavae. They are joined by two pairs of vertical tracts to neuropils lateral to the buccal tube. A model based on the postcephalic organization of the tardigrade nervous system is used to propose a transformation of segmental ganglia that gives an arrangement congruent with the pattern of neuropils in the brain. The analysis suggests that the brain is derived from nervous elements of four segments with the fourth segment having contributed paired dorsal ganglia and their connecting vertical tracts to the first trunk ganglia of the ventral chain. The organization of the head of tardigrades is compared with that of other lobopods and arthropods and several possible key evolutionary innovations are offered. In addition homologous characters for the heads of tardigrades and other lobopods and arthropods are proposed and the nomenclature for the tardigrade cephalic nervous system is discussed.

The presence of males in species of Echiniscus has been reported only as recently as 1987 and is still considered to be rare. However, males have been found to be common in a disproportionately large number of species of this genus found in Australia. Evidence of sexual dimorphism is presented for five species (three of which are new to science), females and males of which are differentiated on the basis of distinctive gonopores. In all five species males are shorter with longer clavae. Males of Echiniscus jamesi sp. nov., Echiniscus rodnae sp. nov. and Echiniscus curiosus sp. nov. have significantly longer claws. In E. rodnae sp. nov. and E. curiosus sp. nov. males have significantly longer lateral trunk appendages and the dorsal trunk appendage combinations of males of the latter are different from those of females. The widespread distribution of bisexual species of Echiniscus in xeric habitats in Australia does not support the current theory that parthenogenetic species are favoured in such environments.