Abstract
Recent years have brought undeniable progress in tardigrade taxonomy, and speciose complexes were detected in a number of phylogenetic lineages. The family Echiniscidae is one such lineage; it is one of the most diverse groups of limno-terrestrial tardigrades and can be characterized as having achieved great evolutionary success. In this contribution, using populations representing several species that originated from the Indomalayan region, we reconstructed phylogenetic affinities within Nebularmis, a recently erected genus within the Echiniscus lineage. Nebularmis auratussp. nov. and Nebularmis burmensissp. nov. are described from the Eastern Yoma Mountains and the Shan Hills (Myanmar), Nebularmis bhutanensissp. nov. is described from the Eastern Himalayas (Bhutan), and Nebularmis indicussp. nov. is described from the foothills of the Western Ghats (Goa, India). Moreover, males are reported in populations of the last two species. All known members of the genus can be phenotypically differentiated based on minute details of their dorsal sculpture and claws. Moreover, a very wide tropical distribution is demonstrated for Nebularmis cirinoi, recorded for the first time from islands of the Malay Archipelago. Furthemore, novel morphological, genetic, and geographic data allowed for the clarification of the generic diagnosis. Currently available data favor a scenario under which Nebularmis evolved in Southeast Asia and later dispersed to other regions of the globe.
Highlights
The diversity of tardigrades has been intensively studied in recent years using modern species delimitation tools, including statistical morphometry and molecular analyses
Pseudechiniscus and Hypechiniscus [3, 4], in the eutardigrade order Apochela, the genus Milnesium was recently demonstrated to be rich in species [5], and examples of hyperdiversity are highly elaborate in the other eutardigrade order, Parachela, which contains such intensively studied genera as Macrobiotus, Ramazzottius, Richtersius, Paramacrobiotus and Platicrista [6,7,8,9,10,11]
Resolving many taxonomic uncertainties enhanced overall tardigrade classification [12] by narrowing the extent of intraspecific variability, which was traditionally considered sizeable [13, 14], and contributed, for example, to the recognition of Hypsibius exemplaris as a new model metazoan species [15] that is crucial in research on animal development and cryptobiosis (e.g., [16, 17])
Summary
The diversity of tardigrades has been intensively studied in recent years using modern species delimitation tools, including statistical morphometry and molecular analyses. High taxonomic importance was typically assigned to dorsal sculpturing in the Echiniscus lineage [24]; recently, following the recognition that the phylogenetic position appeared congruent with morphological data, new monophyletic genera were separated from Echiniscus [25, 26]. One of these genera, Nebularmis, was created for the widespread Palearctic species Nebularmis reticulatus [27, 28] and its kin. Poor species descriptions continue to be a serious problem when linking the traditionally morphologically based Linnean system of classification with the proliferating use of integrative taxonomic methods [30], posing difficulties that threaten the stability and reliability of tardigrade systematics [31]
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