An upgraded comprehensive multilocus phylogeny of the Tardigrada tree of life

Abstract

Providing 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 genus Apodibius and claw reduction across the Tardigrada tree of life. Evolutionary consequences are discussed.

Deceptive conservatism of claws: distinct phyletic lineages concealed within Isohypsibioidea (Eutardigrada) revealed by molecular and morphological evidence

“…During the review process of this manuscript, the tardigrade phylogeny by Guil et al (2019) was published. Consequently, we adjusted the taxonomy of the high ranks in our work to the system proposed in Guil et al (2019), however, in our opinion the new taxonomy is controversial and requires further work: possibly rank shift and taxon membership rearrangements, as the majority of high rank taxa (orders, families) remained in polytomies, compared to the relatively well-resolved relationships from the previous phylogeny by Bertolani et al (2014).…”

“…During the review process of this manuscript, the tardigrade phylogeny by Guil et al (2019) was published. Consequently, we adjusted the taxonomy of the high ranks in our work to the system proposed in Guil et al (2019), however, in our opinion the new taxonomy is controversial and requires further work: possibly rank shift and taxon membership rearrangements, as the majority of high rank taxa (orders, families) remained in polytomies, compared to the relatively well-resolved relationships from the previous phylogeny by Bertolani et al (2014). Given that superfamily Isohypsibioidea was elevated to the order level by Guil et al (2019), according to the article 36.1 of International Code of Zoological Nomenclature (1999), the authorship of the superfamily (Sands et al, 2008) is now superseded by the latest authority.…”

“…Consequently, we adjusted the taxonomy of the high ranks in our work to the system proposed in Guil et al (2019), however, in our opinion the new taxonomy is controversial and requires further work: possibly rank shift and taxon membership rearrangements, as the majority of high rank taxa (orders, families) remained in polytomies, compared to the relatively well-resolved relationships from the previous phylogeny by Bertolani et al (2014). Given that superfamily Isohypsibioidea was elevated to the order level by Guil et al (2019), according to the article 36.1 of International Code of Zoological Nomenclature (1999), the authorship of the superfamily (Sands et al, 2008) is now superseded by the latest authority. Figure 1 Schematic presentation of the oral cavity armature (OCA) in Isohypsibioidea, the first and/or the second band of teeth are marked by Roman numerals: A -a continuous peribuccal lamina, two bands of teeth (Apodibius, Grevenius gen. nov., Halobiotus, Hexapodibius); B -a continuous peribuccal lamina, the first band of teeth (Fractonotus, Isohypsibius, Ursulinius gen. nov.); C -six convex peribuccal papulae, the first band of teeth (Eremobiotus); D -rectangular peribuccal lamellae, the first band of teeth with lateral toothless intervals (Pseudobiotus); E -rectangular peribuccal lamellae, two bands of teeth (Thulinius); F -six large peribuccal lamellae, two bands of teeth (Haplomacrobiotus).…”

“…Despite the undeniable progress in disentangling tardigrade phylogeny, both tardigrade relationships with other metazoans (e.g., Campbell et al, 2011;Gross & Mayer, 2015) and many within-group affinities remain unclear (e.g., Sands et al, 2008;Bertolani et al, 2014a). One of major tardigrade groups with unresolved phylogeny and taxonomy is Isohypsibioidea Guil et al, 2019. This recently established eutardigrade order is considered problematic because it is based on traits that show high levels of morphological stasis (Marley et al, 2011).…”

“…This recently established eutardigrade order is considered problematic because it is based on traits that show high levels of morphological stasis (Marley et al, 2011). In fact, this group was erected relatively late mainly because for decades various taxa with Isohypsibius and Hypsibius type claws were traditionally grouped into a single order Hypsibioidea Guil et al, 2019. Although the erection of Isohypsibioidea clarified the taxonomy of the Eutardigrada, the few efforts to resolve phylogenetic relationships within the order suffered from insufficient sampling and resulted in prevailing polytomies Gąsiorek et al, 2019).…”