An upgraded comprehensive multilocus phylogeny of the Tardigrada tree of life

Abstract

AbstractProviding accurate animals’ phylogenies rely on increasing knowledge of neglected phyla. Tardigrada diversity evaluated in broad phylogenies (among phyla) is biased towards eutardigrades. A comprehensive phylogeny is demanded to establish the representative diversity and propose a more natural classification of the phylum. So, we have performed multilocus (18S rRNA and 28S rRNA) phylogenies with Bayesian inference and maximum likelihood. We propose the creation of a new class within Tardigrada, erecting the order Apochela (Eutardigrada) as a new Tardigrada class, named Apotardigrada comb. n. Two groups of evidence support its creation: (a) morphological, presence of cephalic appendages, unique morphology for claws (separated branches) and wide‐elongated buccopharyngeal apparatus without placoids, and (b) phylogenetic support based on molecular data. Consequently, order Parachela is suppressed and its superfamilies erected as orders within Eutardigrada, maintaining their current names. We propose a new classification within the family Echiniscidae (Echiniscoidea, Heterotardigrada) with morphological and phylogenetic support: (a) subfamily Echiniscinae subfam. n., with two tribes Echiniscini tribe n. and Bryodelphaxini tribe n.; (b) subfamily Pseudechiniscinae subfam. n., with three tribes Cornechiniscini tribe n., Pseudechiniscini tribe n. and Anthechiniscini tribe n.; and (c) subfamily Parechiniscinae subfam. n., with two tribes Parechiniscini tribe n. and Novechiniscini tribe n. Reliable biodiversity selection for tardigrades in broad phylogenies is proposed due to biased analyses performed up to now. We use our comprehensive molecular phylogeny to evaluate the evolution of claws in the clawless genusApodibiusand claw reduction across the Tardigrada tree of life. Evolutionary consequences are discussed.