Phylogeny of the asexual lineage Murrayidae (Macrobiotoidea, Eutardigrada) with the description of Paramurrayon gen. nov. and Paramurrayon meieri sp. nov.

The peculiar family Murrayidae, comprising the genera Murrayon, Dactylobiotus and Macroversum, contains relatively rare species living in hydrophilic and freshwater habitats on all continents, and contains two of the six exclusively freshwater tardigrade genera. This family probably represents an example of the evolution and persistence of an asexual lineage that differentiated into several taxa without sexual reproduction. Analyses of nuclear and mitochondrial genes (18S, 28S, ITS2 and cox1), and the increase of five taxa to the phylogenetic analyses of Murrayidae led us to infer that Murrayon is polyphyletic, being composed of two "species groups' that also find morphological supports: the "dianeae group' characterised by peculiar egg processes (rod-shaped and covered with a cuticular layer), animals with large, evident epicuticular pillars and small claws; and the "pullari group' characterised by conical egg processes, animals with very small epicuticular pillars, and proportionally larger and longer claws. This latter group is a sister group to Dactylobiotus. Murrayon hastatus is the only species within the genus that has an uncertain position with eggs of the "dianeae group' and animals of the "pullari group'. We propose the erection of Paramurrayon gen. nov. (for the "dianeae group' of species), the emendation of Murrayon, and new taxonomic keys for both genera. Possible scenarios of the evolution of taxa within Murrayidae are hypothesised based on synapomorphic characters. Paramurrayon meieri sp. nov. from Norway is described with an integrative approach. Photographs of type material of Murrayon stellatus, Murrayon nocentiniae, Murrayon ovoglabellus and Macroversum mirum are shown for the first time, together with descriptions of new characters. Murrayon hibernicus is considered as nomen dubium and Murrayon hyperoncus is transferred to Macrobiotus pending further analyses.