Eupentarius Reitter

Jałoszyński, Paweł, 2022, Taxonomy of ' Euconnus complex'. Part XXIV. Intermediate forms between Psomophus, Eupentarius and Euconnus s. str. in the East Palaearctic fauna unify problematic subgenera (Coleoptera, Staphylinidae, Scydmaeninae), Zootaxa 5194 (3), pp. 343-391 : 382-384

2. Eupentarius Reitter

(= Euconophron Reitter ) placed as a junior synonym of Euconnus s. str.

As discussed previously ( Jałoszyński 2017b), the diagnosis of Eupentarius is somewhat unclear. Better known under its junior synonymic name Euconophron , this subgenus was originally based on characters with no true taxonomic value, known today to be highly variable: elytral bases broader than the pronotal base and bearing distinct basal impressions and the ‘humeral fold’ (i.e., the elongate humeral callus demarcated mesally by impression); the antennal club tetramerous and not sexually dimorphic; the head and pronotum similarly setose; and the pronotum with a transverse antebasal groove ( Reitter 1909). Later, in one of the early papers by Franz (1957), in an attempt to ‘save’ Euconophron , this diagnosis was modified to include large, coarsely faceted eyes; bristles on the posterior portion of the head capsule; the pronotum not much broader than the head; the anterior portion of the pronotal disc with a heart-shaped field of a translucent cuticle; the pronotal base with a transverse groove accompanied by four antebasal pits, lacking median carina; the elytra behind the (not visible) scutellum often flattened, not evenly convex; and the aedeagus always with a bifid apex, with plate-like or tooth-like endophallic sclerites. As the diagnosis of Euconophron still remained highly problematic, it was further discussed by Vít (2005), in another attempt to justify the existence of this problematic taxonomic entity. He noticed that western Palaearctic species have a uniquely shaped, deeply emarginate or bifurcate aedeagal apex. All these features were discussed in Jałoszyński (2017b), and most of them were found irrelevant as they were too variable within Euconnus . The latter author concluded that: “At least European species of Euconophron share unique characters that suggest that they may form a monophyletic unit and justify a placement of Euconophron as a separate subgenus of Euconnus . These characters include: i) extremely long and slender mandibles with very short basal part and one submedian mesal tooth; ii) the pronotum with a distinct median pit; iii) the prosternum with subtriangular lateral lobes projecting anteriorly in front of procoxae; iv) and the apical portion of aedeagus deeply emarginated/bifurcated.”

The situation is further complicated by the fact that Franz 1957 ‘redescribed’ the type species of Euconophron based on most likely misidentified material, and the holotype is a female (discussed in detail by Jałoszyński (2017b)). For this reason, it was not possible to verify whether the bifurcate aedeagal apex, the presumed diagnostic feature of Euconophron , occurs in its type species.

All the above-mentioned authors (including myself) made efforts to preserve this subgenus as a separate taxonomic unit, despite the Reitter’s very first diagnosis having been already demonstrated to be entirely useless to define a genus-group taxon. The reason was the same as that behind maintaining for such a long time similarly unclear subgenera, as Napochus or Pycnophus ( Jałoszyński 2021a) ‒ in Europe these subunits of Euconnus seemed to be so distinct and so different one from another that efforts were made not to merge them into larger and more diverse units. However, such an approach fails when extra-European Euconnus species are considered.

Four clearly defining characters listed above seem sufficient to maintain Eupentarius (placed as a senior synonym of Euconophron only recently; see Jałoszyński (2021b)). However, morphological features of the newly revised East Palaearctic Euconnus taiwanus group diffuse such a diagnosis. The long mandibles with short basal portions and single submedian mesal tooth are hardly useful to define a subgenus, as the mandibular structure within Euconnus is extremely diverse. Even within European ‘ Psomophus ’ or Tetramelus Motschulsky , a great diversity of structures was illustrated (e.g., Orousset (2015, 2018)). The form of mandible thought to be unique for Eupentarius can be found e.g., in E. (Tetramelus) pandellei ( Fairmaire, 1859) . The median pronotal pit seemed to be unique for Eupentarius . However, this pit can be a remainder of the reduced transverse antebasal groove and it certainly cannot be a sole diagnostic character. It was found e.g., in the newly described E. urauchianus , which does not have any other diagnostic features of Eupentarius . The prosternal lateral subtriangular lobes projecting to a various extent anteriorly in front of procoxae were demonstrated to occur also in Androconnus Franz , Cladoconnus Reitter , Tetramelus and at least some species of Euconnus s. str. ( Jałoszyński 2021b). The apical portion of the aedeagus deeply emarginate or bifurcate seemed the strongest diagnostic feature supporting a separate status of Eupentarius , until the revision of the E. taiwanus species group presented herein.

The E. taiwanus group is very interesting in terms of character variability. Its species externally resemble European Euconnus previously placed in Eupentarius / Euconophron in the shape of the pronotum, which is narrowing both posterad and anterad, but with the posterior margin much longer than the anterior one. However, they do not have the median antebasal pronotal pit. The lateral prosternal lobes are developed and subtriangular, clearly projecting anterad. The antennal club, typically tetramerous in Eupentarius (unless unusually modified in males, which may have pentamerous clubs), is, however, clearly trimerous. Interestingly, unlike the club in the ‘true Psomophus ’, i.e., the E. callidus species group, antennae are strikingly short in relation to the body and the antennomere 9 is of intermediate size between 8 and 10. Although externally this group is extremely uniform and includes some species pairs that can be distinguished only by the aedeagus, the male genital structures are unexpectedly diverse. The aedeagus of E. taiwanus has truncate or indistinctly concave apex; in E. fukiensis the apex is strongly bifurcate (like in many species included in Eupentarius ); in E. bibaculatus the apex is narrow and subtriangular, convex, while in E. cryptoiriomotensis and E. oitaensis the dorsal apical plate that forms the aedeagal apical region is extremely short and shallowly emarginate. In E. banana , which otherwise is very similar to other species of the E. taiwanus complex, the aedeagus is unlike any other within this group, strongly sclerotized, with apically convex dorsal apical plate, apically concave ventral apical plate, asymmetrical endophallic sclerites, and even parameres unusually fused with the median lobe along their proximal ventral margins (a highly unusual feature for Euconnus ). Moreover, the aedeagus of E. bibaculatus bears a pair of unique lateral distal projections, not known in any other species of this group. The male secondary sexual characters are also unusual. They are present only in E. fukiensis (steeply sloping and modified elytral apex) and in E. banana (strongly curved terminal mesotarsomere and ventral denticles on mesotarsomeres 3 and 4). Euconnus fukiensis is closest to the diagnosis of Eupentarius : it has two out of four characters defining that subgenus: the lateral lobes of the prosternum and the bifurcate aedeagal apex. On the other hand, the trimerous antennal club would place it (and all remaining species of the E. taiwanus group) in Psomophus , even though all these species are strikingly dissimilar to E. callidus .

There are two possible actions available to avoid placing species of the E. taiwanus group as Euconnus incertae sedis (the most undesirable solution, which would only increase the chaos in Euconnus ): (i) to merge Euconnus s. str., Psomophus and Eupentarius into one taxonomic entity, or (ii) to propose a new subgenus. The latter option is hardly possible because of lack of reliable diagnostic features. The E. taiwanus group is defined by the antennae remarkably short and compact, with trimerous clubs (the feature overlapping with the diagnosis of Psomophus ), but the antennomere 9 always much narrower than 10; the pronotum rounded at sides, broadest slightly behind middle or at middle, and with two pairs of antebasal pits (this feature can be found in other subgenera, especially in Euconnus s. str.). All members have a distinctly elongate head, with strongly elevated supraantennal tubercles narrowly separated at middle and the vertex slightly bulging posterodorsad; the pronotal base with two pairs of pits, of which inner pair is slightly larger than outer pair, lacking transverse groove or connected by faint, barely discernible groove; and thick bristles distributed on tempora, vertex and sides of pronotum. Aedeagi are so diverse that it is not possible to include any genital characters into the diagnosis of this group. Founding a new subgenus on such a combination of characters does not seem to solve any taxonomic problems within Euconnus .

Consequently, I propose here not only to place Psomophus as a junior synonym of Euconnus . s. str., but also Eupentarius as a junior synonym of Euconnus s. str.