Adropion, Pilato, 1987

Gąsiorek, Piotr, Blagden, Brian, Morek, Witold & Michalczyk, Łukasz, 2024, What is a ‘ strong’ synapomorphy? Redescriptions of Murray’s type species and descriptions of new taxa challenge the systematics of Hypsibiidae (Eutardigrada: Parachela), Zoological Journal of the Linnean Society 202 (1), pp. 1-63 : 12

Composition of Adropion

The genus Adropion was inferred as polyphyletic by Bertolani et al. (2014). Gąsiorek and Michalczyk (2020) confirmed the non-monophyly of Adropion and established Guidettion (the latter having only three bar-like macroplacoids in the pharynx). However, the genus is still heterogeneous in terms of the number of macroplacoids: the majority of species exhibit three placoids, whereas there is a small group of species with only two macroplacoids, i.e. A. belgicae , A. diphasconiellum comb. nov. et stat. rev., and A. gani . The adoption of molecular phylogenetic methods in tardigrade research has shown that the number and shape of placoids in the pharynx is indicative of common ancestry (e.g. Gąsiorek et al. 2019, Guidetti et al. 2022). Thus, it is plausible that A. belgicae and A. diphasconiellum comb. nov. et stat. rev. are closely related and represent a separate evolutionary lineage. If reciprocal monophyly is confirmed molecularly, they should be erected as a new genus. However, A. gani is designated as nomen inquirendum, because having two rod-like macroplacoids arranged in parentheses (i.e. as in the members of the genus Pilatobius ) it does not fit the current diagnosis of Adropion . Moreover, recently three species of Adropion , each with three placoids, were transferred to Kararehius ( Zawierucha et al. 2023) . Their systematic affinity remains to be verified genetically.