Data from new taxa infer Isoechiniscoides gen. nov and increase the phylogenetic and evolutionary understanding of echiniscoidid tardigrades (Echiniscoidea: Tardigrada)

The marine heterotardigrades belonging to Echiniscoididae inhabit a wide range of substrates and represent the dominant tardigrade group in intertidal zones worldwide. Notably, the evolution of this family is interesting as it holds key evidence as to how heterotardigrades colonized terrestrial and freshwater environments. We inferred the phylogeny of Echiniscoididae using 28S and COI sequences from GenBank and from new specimens collected at Roscoff, France. Morphological characterizations of several major clades, inferred from the molecular data, are currently lacking. However, one of the clades is erected as a new taxon, Isoechiniscoidesgen. nov., for the former Echiniscoides higginsi-group, which comprises species with isonych claws, pillars in the epicuticle and exceptionally long sensory appendages. The type species for the new genus is described here as Isoechiniscoides sifaenov. gen., sp. nov. Isoechiniscoides comprises six clawed interstitial species, whereas Echiniscoides taxa possess a higher claw number and primarily inhabit algae, barnacles and lichens in tidal zones. The new genus, Isoechiniscoides, together with morphologically undetermined specimens from British Columbia (Canada), is sister-group to all other Echiniscoididae taxa. Consequently, we propose to establish Isoechiniscoidinae subfam. nov. to accommodate the new genus. Isoechiniscoidinae provides an evolutionary link between Echiniscoidea and Arthrotardigrada. The latter comprises exclusively marine and mostly interstitial species.