Thaumastocephalini, Jałoszyński & Hlaváč & Anlaş, 2023

Jałoszyński, Paweł, Hlaváč, Peter & Anlaş, Sinan, 2023, Percussiopalpus gen. n. from Turkey, a free-living relative of cave-dwelling Thaumastocephalus, and revised placement of Thaumastocephalini (Coleoptera: Staphylinidae: Pselaphinae), Zootaxa 5277 (1), pp. 71-90 : 87

Placement of Thaumastocephalini

As mentioned in the Introduction, characters that support the current placement of Thaumastocephalini as a tribe within Batrisitae are problematic. The discovery in both Percussiopalpus and Thaumastocephalus of one pair of peg-like sensilla on the anteroventral margin of the labrum excludes these genera from Batrisitae, which are characterized by four such sensilla ( Kurbatov 2007).

In fact, Thaumastocephalini , apart from their highly peculiar maxillary palps (but see further discussion concerning structures in Mayetiini) show a set of features typical of Euplectitae . Chandler (2001a) redefined Euplectitae as a group that shows the following characters (with morphological terminology updated and ambiguous characters omitted): (1) meso- and metatrochanters with the posterodistal angle acute; (2) the anterobasal femoral region close to the coxo-trochanteral articulation (i.e., not widely separated from it); (3) one tarsal claw reduced, often setiform; and (4) tarsomeres 2 and 3 longer than tarsomere 1. These characters are relatively weak in terms of suprageneric taxonomy, and not surprisingly, there is a growing evidence that the supertribe Euplectitae is a polyphyletic assemblage and not a clade ( Parker & Maruyama 2013; Parker 2016; Jałoszyński et al. 2022). It is beyond the scope of this study to clarify the suprageneric system of Pselaphinae. We transfer Thaumastocephalini from Batrisitae into Euplectitae , based on the presence of all the diagnostic features listed above. With this transfer, the Euplectitae comprise nine tribes: Bythinoplectini, Dimerini, Euplectini, Jubini, Mayetiini, Metopiasini, Thaumastocephalini , Trichonychini , and Trogastrini.

The subdivision (i.e., the tribal and subtribal classification) of a likely non-monophyletic Euplectitae is naturally also problematic. Thaumastocephalini show the only apparently unambiguous diagnostic feature of the tribe Trichonychini listed by Chandler (2001a): the male sternite IX tripartite, with a ‘penial plate’. All remaining characters included in the diagnosis of Trichonychini are ambiguous and do not occur in all genera of this tribe, as mentioned already by Chandler (2001a), who redefined the tribe. As Thaumastocephalini clearly differ from Trichonychini in (1) derived, strongly modified maxillary palps with spherical appendages inserted on long peduncles (in Trichonychini unmodified palps with pipe-shaped palpomere 2, subtriangular palpomere 3 and fusiform palpomere 4, lacking any peculiar features); (2) prominent submental bulge strongly projecting ventrad (lacking in Trichonychini ), separate placement of these tribes is maintained. However, the tripartite male sternite IX and broadly separated metacoxae (at least in some Trichonychini ) suggest a possible sister-group relationship between Thaumastocephalini and Trichonychini , and within the latter tribe to Trichonychina. Members of Trichonychina and Thaumastocephalini share the same mesoventral foveal pattern (Chandler 2001, fig. 3). However, remarkable differences in the structure of maxillary palps, and the peculiar shape of the head capsule with the prominent submental bulge in Thaumastocephalini can be used to distinguish these groups. Further study is required to clarify the classification of ‘Euplectitae’, and especially a hypothesis of a possible monophyly of Thaumastocephalini + Trichonychina should be tested, with a broad taxon sampling.