Euconnus (Psomophus), Casey, 1897

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

1. Psomophus

Casey placed as a junior synonym of Euconnus s. str.

Psomophus was established for Nearctic species and defined using several characters, of which Jałoszyński (2017c) retained only trimerous antennal clubs as the sole diagnostic feature. He also remarked that “all other structures are very similar to those of Euconnus s. str. and it is possible that in future these taxa will be merged” ( Jałoszyński 2017c).

The well-known Nearctic, European and East Asian species included in Psomophus , e.g., E. callidus , E. intrusus ( Schaum, 1844) , E. regimbarti Croissandeau, 1893 , E. wetterhallii ( Gyllenhal, 1813) , E. kraatzi Reitter, 1882 , E. debilis , E. nuperus , E. chinensis , and the newly described E. multiinsularis share a similar structure of the aedeagus and the protibiae in males curved or bent at apices (illustrated e.g., in Jałoszyński (2017c, 2022) and Orousset (2018)). However, some European species do not have any noticeable male sexual secondary characters, e.g., E. pyrenaeus Xambeu, 1889 or E. chekiri Orousset, 2018 , and the newly described E. rectitibia is also devoid of the protibial modification. All these species have clearly delimited trimerous antennal clubs. Because the shape of the pronotum is variable already within the European and Nearctic species of Psomophus , in most species narrowing anterad with rounded sides, but broadest near middle in E. callidus , indistinctly in front of middle in E. wetterhallii , or clearly in front of middle in E. kraatzi , this feature does not differentiate Psomophus as a distinct subgenus.

Findings of East Palaearctic (all Japanese) species with clearly trimerous clubs, as E. kirin , E. yaimanus and E. uchinaanchu , makes this sole antennal feature to define Psomophus even more problematic. These species have aedeagi remotely similar to those of the above-mentioned Psomophus species, more resembling those of the former subgenus Napochus Thomson , which is now a junior synonym of Euconnus s. str. These three Japanese species are undoubtedly closely related one to another, as they share unusual cephalic modifications in males, not known in any Psomophus (weakly expressed but present in E. uchinaanchu ), slender and strongly convex body form, endophalli with subapical median groups of elongate sclerites, and parameres with numerous setae of various lengths. The shapes of pronota differ among the E. kirin group ‒ almost subconical and broadest behind middle in E. kirin and E. yaimanus , but nearly round and broadest very indistinctly behind middle in E. uchinaanchu . All features except for the trimerous antennae place the E. kirin group in Euconnus s. str.

While exploring further the Japanese fauna of Euconnus , I encountered another group of species that makes the diagnosis of Psomophus even more problematic. Euconnus pseudotrimerus and E. urauchianus are similar to each other in having a ‘ Napochus -like’ body form (i.e., the subconical pronotum and large antennal clubs almost as long as half-length of antenna) and also in the ‘ Napochus -like’ form of the aedeagus (especially in having a pair of distal lateral projections between the ventral and dorsal apical plates, near the apex of the former). However, the antennal club in E. pseudotrimerus is not exactly tetramerous. The antennomere 8 is so small that it could be interpreted as indistinctly tetramerous or indistinctly trimerous. This problem is even greater in the case of E. urauchianus , which has the three terminal antennomeres clearly enlarged and sharply demarcated, but the antennomere 8 is still somewhat enlarged, although it is only indistinctly broader than antennomere 7. Whether such a club should be treated as trimerous or tetramerous, depends on interpretation. If E. urauchianus is placed in Psomophus , then the ‘trimerous club’ would become a highly unclear diagnostic feature for this subgenus.

I prefer to remove this problematic feature (i.e., the number of antennomeres forming the club) from the diagnosis of Psomophus . This leaves no reliable characters to define Psomophus , and consequently, Psomophus is placed as a junior synonym of Euconnus s. str.

Discussion concerning another group of eastern Asian Euconnus spp. with trimerous antennal clubs, the E. taiwanus group, is given below, as these species, apart from the unusual antennal structure, resemble members of the subgenus Eupentarius Reitter.