Revised Cornechiniscus (Heterotardigrada) and new phylogenetic analyses negate echiniscid subfamilies and tribes.

Piotr Gąsiorek,Łukasz Michalczyk

doi:10.1098/rsos.200581

Abstract

Echiniscidae are undoubtedly the most thoroughly studied lineage of the class Heterotardigrada. Recently, new subfamilies and tribes grouping echiniscid genera based on traditionally recognized morphological clues have been proposed. Here, by integrative analyses of morphology and DNA sequences of numerous populations of a rare genus Cornechiniscus, we show that this hypothesized classification is artificial. Specifically, we demonstrate that Echiniscinae are diphyletic, as Bryodelphax forms a distinct phyletic lineage within Echiniscidae, and Pseudechiniscinae are polyphyletic, with Mopsechiniscus being indirectly related to Pseudechiniscus, which is closer to the Echiniscus-like genera than to other genera with pseudosegmental plates. Consequently, the subfamilies and tribes are considered as unsupported from the phylogenetic and morphological point of view. The genus Cornechiniscus is revised, and the phenotypic diagnoses of several species are updated thanks to new rich material from Africa, Asia and Europe. Cornechiniscus imperfectus sp. nov. is described from mountains of Kyrgyzstan, being the second appendaged species within the genus and the third known to exhibit dioecy. A taxonomic key to the genus is provided. Systematic positions of Acanthechiniscus and Multipseudechiniscus are also discussed. Acanthechiniscus goedeni is confirmed to be a member of the genus Acanthechiniscus.

Highlights

Tardigrades belong to the superclade of moulting animals, the Ecdysozoa [1,2]
Type materials of C. brachycornutus [27], C. ceratophorus [28], C. holmeni [29], C. lobatus [30], C. madagascariensis [31], C. schrammi [32], C. subcornutus [25], C. tibetanus [33], Multipseudechiniscus raneyi [34] and Acanthechiniscus goedeni [34] deposited in the Natural History Museum of Verona, Italy and the Natural History Museum of Denmark were examined using LCM
The Bayesian inference (BI) and maximum likelihood (ML) phylogenetic analyses of the family Echiniscidae based on conservative nuclear markers, 18S and 28S rRNA, showed that Bryodelphax was the sister genus to all other echiniscids

Summary

Introduction

The level of understanding of phylogenetic relationships within tardigrade lineages is diversified, as some royalsocietypublishing.org/journal/rsos R. Despite the continuous effort in obtaining novel genetic and morphological data for echiniscid species, resulting in the establishment of new genera, such as Multipseudechiniscus [10], Diploechiniscus [11], Acanthechiniscus [5] and Stellariscus [12], and improved comprehension of morphological diversity within the already established genera [12,13,14,15,16,17,18], echiniscid phyletic relationships are not well resolved [19]. There are two echiniscid clades commonly accepted as monophyletic and supported in various phylogenetic analyses: the Echiniscus lineage (((Hypechiniscus (Testechiniscus (Diploechiniscus + Echiniscus-like genera))) and the clade comprising ((Proechiniscus (Acanthechiniscus + Cornechiniscus)) [5,12,20]. The subdivision and arrangement of dorsal plates were used as putative synapomorphies for these taxonomic ranks, molecular phylogenies presented therein did not support some (Pseudechiniscinae), or lacked genetic information for certain genera (e.g. Multipseudechiniscus, Novechiniscus)

Methods

Results

Conclusion