Spiny bears: a new species of Ramazzottius (Eutardigrada: Ramazzotidae) from Mexico unveils a hidden clade within the genus

Species description constitutes a fundamental endeavour, as it lays the foundation for subsequent disciplines which require precise identifications. Nevertheless, species must be regarded as hypothetical constructions requiring validation through diverse lines of evidence. Most of the Ramazzottius species were described with limited information according to contemporary standards, underscoring the need to integrate morphological and molecular data in new species descriptions. This study presents the first new species of Ramazzottius from Mexico found in lichen samples. Morphological assessment comprised light and electron microscopy imaging as well as linear morphometrics. Uncorrected p-distance calculations, Assemble Species by Automatic Partitioning (ASAP), and Poisson Tree Processes (PTP) were applied for molecular species delimitation, using the genes COI and ITS-2. Additionally, phylogenetic relationships within the genus Ramazzottius were reconstructed through maximum likelihood and Bayesian inference approaches, concatenating fragments of four genes: 18S, ITS-2, 28S and COI. The new species Ramazzottius suzithuae sp. nov. exhibits morphological similarity to Ramazzottius belubellus but is distinguished by a particular arrangement of the spines on the dorsal cuticle. All delimitation analyses confirm the molecular distinctiveness of the new species and the existence of at least two species within “Ramazzottius cf. saltensis”. The multi-locus tree recovered five major clades and positions the new species close to these Ramazzottius cf. saltensis species in their own clade, separated from the “baumanni” species grouped in another clade. The lack of complete and consistent diagnostic traits for all these clades still prevents the erection of separate genera.