Abstract
Abstract Pseudechiniscus is the second most species-rich genus in Heterotardigrada and in the family Echiniscidae. However, previous studies have pointed out polyphyly and heterogeneity in this taxon. The recent erection of the genus Acanthechiniscus was another step in making Pseudechiniscus monophyletic, but species identification is still problematic. The present investigation aims at clarifying biodiversity and taxonomy of Pseudechiniscus taxa, with a special focus on species pertaining to the so-called ‘suillus–facettalis group’, by using an integrated approach of morphological and molecular investigations. The analysis of sequences from specimens sampled in Europe and Asia confirms the monophyly of the genus Pseudechiniscus. Inside the genus, two main evolutionary lineages are recognizable: the P. novaezeelandiae lineage and the P. suillus–facettalis group lineage. Inside the P. suillus–facettalis group, COI molecular data points out a very high variability between sampled localities, but in some cases also among specimens sampled in the same locality (up to 33.3% p-distance). The integrated approach to the study of Pseudechiniscus allows confirmation of its monophyly and highlights the relationships in the taxon, pointing to its global distribution.
Highlights
The phylum Tardigrada consists of more than 1200 described species (Guidetti & Bertolani, 2005; Degma & Guidetti, 2007; Degma et al, 2018), subdivided into three classes: Eutardigrada, Mesotardigrada and Heterotardigrada (Ramazzotti & Maucci, 1983)
Tardigrades (53 specimens) were mounted in Faure– Berlese mounting medium for observations under light microscopy (LM), while the other 28 animals were prepared for scanning electron microscopy (SEM), following the protocol described in Bertolani et al (2011b)
Our new data confirm the subdivision between Acanthechiniscus and Pseudechiniscus identified by Vecchi et al (2016) and points out that all specimens sampled in European, Asian, Arctic and Antarctic regions belong to Pseudechiniscus. This highlights the global distribution of Pseudechiniscus, differing from what was recently discovered for another echiniscid genus (i.e. Testechiniscus; Gąsiorek et al, 2018a)
Summary
The phylum Tardigrada consists of more than 1200 described species (Guidetti & Bertolani, 2005; Degma & Guidetti, 2007; Degma et al, 2018), subdivided into three classes: Eutardigrada, Mesotardigrada and Heterotardigrada (Ramazzotti & Maucci, 1983). Maucci (1973–74) and Dastych (1984) suggested a complete revision of the genus It was emended by Kristensen (1987), but two main groups inside the genus were still distinguished: the P. suillus/conifer group, characterized by the absence of trunk cirri; and the P. victor group, identifiable with the presence of trunk cirri. A recent integrative analysis (Vecchi et al, 2016) has led to the erection of the genus Acanthechiniscus, more or less corresponding to the old P. victor group, another step in making Pseudechiniscus monophyletic, with the genus comprising 40 described species (Degma et al, 2018)
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