Abstract
The taxonomy of many groups of meiofauna is challenging due to their low number of diagnostic morphological characters and their small body size. Therefore, with the advent of molecular techniques that provide a new source of traits, many cryptic species have started to be discovered. Tardigrades are not an exception, and many once thought to be cosmopolitan taxa are being found to be complexes of phenotypically similar species. Macrobiotus pallarii Maucci, 1954 was originally described in South Italy and has been subsequently recorded in Europe, America, and Asia. This allegedly wide geographic range suggests that multiple species may be hidden under this name. Moreover, recently, genetic evidence to support this was put forward, and the Macrobiotus pallarii complex has been proposed to accommodate putative species related to M. pallarii. Here, we describe three new pseudocryptic species based on populations that would have been all classified as Macrobiotus pallarii if molecular methods were not employed. Using an integrative taxonomy approach, we analyzed animals and eggs from the topotypic population of Macrobiotus pallarii, together with four other populations of the complex. We recovered four distinct phylogenetic lineages that, despite the overlap of morphometric traits, can be separated phenotypically by subtle but discrete morphological characters. One lineage corresponds to Macrobiotus pallarii, whereas the other three are newly described as Macrobiotus margoae Stec, Vecchi & Bartels, sp. nov. from the USA, Macrobiotus ripperi Stec, Vecchi & Michalczyk, sp. nov. from Poland and Finland, and Macrobiotus pseudopallarii Stec, Vecchi & Michalczyk, sp. nov. from Montenegro. To facilitate species identification, we provide a dichotomous key for species of the M. pallarii complex. Delimitation of these pseudocryptic taxa highlights the need for an integrative approach to uncover the phylum’s diversity in full.
Highlights
Tardigrades constitute a phylum of microinvertebrates inhabiting both terrestrial and aquatic habitats worldwide [1], with approximately1300 species known so far [2,3,4]
To facilitate species identification, we provide a dichotomous key for species of the M. pallarii complex
Dichotomous diagnostic key to species of the Macrobiotus pallarii complex To facilitate species identification, we provide a dichotomous key to the valid species of the M. pallarii complex
Summary
Tardigrades constitute a phylum of microinvertebrates inhabiting both terrestrial and aquatic (freshwater and marine) habitats worldwide [1], with approximately1300 species known so far [2,3,4]. Many studies using an integrative taxonomy approach have recently revealed that various tardigrade species once thought to be widespread are complexes of cryptic species with more localized distributions [5, 6, 11, 12]. In addition to their distribution, tardigrade cryptic species have been shown to diverge based on reproductive mode [13], ploidy [5], and anhydrobiotic survival [14]. The class Heterotardigrada encompasses both primarily marine tardigrades (Arthrotardigrada) and mostly limnoterrestrial armoured tardigrades (Echiniscoidea)
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