Ongoing revision of Echiniscoididae (Heterotardigrada: Echiniscoidea), with the description of a new interstitial species and genus with unique anal structures

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.