Euconnus Cladoconnus Reitter, 1909

Caterino, Michael S., 2022, First report of the Euconnus Thomson subgenus Cladoconnus Reitter in the New World, represented by thirteen new Appalachian species (Coleoptera, Staphylinidae, Scydmaeninae), ZooKeys 1137, pp. 133-175 : 133

Subgenus Euconnus Cladoconnus Reitter, 1909

Cladoconnus Reitter, 1909: 226, as subgenus of Euconnus Thomson. Type species: Scydmaenus motschulskii Motschulsky, 1837 (subsequent designation by Newton and Franz 1998: 145).

Euconnus (Cladoconnus) Reitter: Hlavác and Stevanović 2013 (diagnosis); Jałoszyński 2018 (diagnosis).

Diagnosis.

Previous diagnoses of Palaearctic Cladoconnus have focused primarily on the presence in males of serrulate carinae on the inner margins of antennomeres VIII and IX, a character not known elsewhere in Euconnus . Jałoszyński (2018) further noted the unique presence of a bell-shaped, setose pronotum with 3 basal foveae in an inward-pointing triangular arrangement on each side of a short median basal pronotal carina, straddling short sublateral carinae. He also noted a unique mandibular shape in which the outer margin is interrupted where the apical portion narrows abruptly. The species described here do not entirely conform to this diagnosis, showing variability in most of these characters among them. All are small, with total body lengths ranging from 1.3 to 1.7 mm, not differing much between the sexes (Table 1 ). The highly distinctive male antennal carinae are evident in most of these species (Figs 4E , 6 , 9E , 14C , 16C ), but are completely absent in a couple that otherwise seem to be related by other morphological characters and by DNA sequences (Figs 1E , 8A , 13E ). Most are consistent in having a bell-shaped pronotum, narrowed basally in some, with the triangle pattern of posterior foveae and at least short sublateral carinae (Figs 4F , 9F ). A median basal pronotal carina is evident in several (e.g., Fig. 4F ), but in others it is so weak as to be essentially absent (e.g., Fig. 9F ). Only one species ( E. vetustus ) exhibits the distinctive bi-arcuate mandible, the others appearing to have simply arcuate mandibles. Similar to all Palaearctic species, American Cladoconnus have male genitalia with complex, asymmetrical endophallic armature. Metathoracic wings have not been described for European species, but illustrations and descriptions of body and metathoracic shape suggest that most described species are fully winged in both sexes. Hoshina et al. (2018) notes apparent sexual dimorphism in wingedness in three Asian species. Several of the new American species are flightless in both sexes, and some appear to be flightless in females only. Females associated by sequencing show reduced eyes relative to males, and have smaller, unmodified antennomeres, in several species having the club reduced to only three antennomeres (e.g., Fig. 9D ). Due to this variability, it is likely that future revision of Cladoconnus will be necessary, but for now these new species seem to have clear relationships to those in the Old World, and are relatively easy to recognize among New World Euconnus .

There is little point writing a key to these species because most can only definitely be identified by male genitalia, with a few externally similar species even sympatric in a few places. There are three main morphotypes, dark and stout ( Euconnus vexillus and E. vetustus ), dark with rufescent highlights, more gracile ( Euconnus megalops ), and small and pale (flightless), with a mix of modified and non-modified male antennomeres (all remaining species). All share a generally similar form of male genitalia: the basal bulb is large and voluminous, narrowing at the shoulders to a variously tapered median lobe (sensu Stephan et al. 2021; equivalent to the dorsal apical projection of Jałoszyński 2012. The opposite side (morphologically ventral) exhibits a thin, weakly sclerotized compressor plate (sensu Stephan et al. 2021; equivalent to the ventral apical projection of Jałoszyński 2012). They all have a crescent-shaped diaphragm plate sclerite, and relatively thin, weakly curving parameres, bearing a small number of apical setae. They vary much more, however, in the sclerites of the endophallus, which are always asymmetrical, including two or more long, curving, often opposing hooks or spikes. These may bear secondary hook-like processes, or other variously acute projections. In descriptions ‘upper’ and ‘lower’ are used to refer to the diaphragm and foramen sides, respectively, and ‘left’ and ‘right’ referring to the structures as drawn (upper side up), not to true morphological position.

Figures

Figure 1. Habitus and character photos of Euconnus megalops A male, lateral view B female, lateral view C male, dorsal view D female, dorsal view (BgBld. B. 349) E SEM of male head, lateral F SEM of female head, lateral.

Figure 4. Habitus and character photos of Euconnus vexillus A male, dorsal view B female, dorsal view C SEM of mouthparts, ventral view D SEM of female head, lateral E SEM of male antenna, lateral F SEM of elytra and pronotum G SEM of meta- and mesoventrites.

Figure 6. Antennal carina of E. cumberlandus.

Figure 8. Habitus and character photos of Euconnus vetustus A male habitus, dorsal (BBK. A. 020) B male habitus, lateral (GRB. A. 336) C SEM of protibial setae.

Figure 9. Habitus and character photos of Euconnus falcatus A male, lateral view B female, lateral view C male, dorsal view D female, dorsal view E SEM, male antenna F SEM, pronotum and elytra G SEM, female head, lateral view H SEM, male head, anterior view.

Figure 13. Habitus and character photos of Euconnus attritus A male, lateral view B male, dorsal view C female, lateral view D female, dorsal view E SEM of male antenna F SEM of venter of head.

Figure 14. Habitus and character photos of Euconnus adversus A male, lateral view B male, dorsal view (NT. A. 009) C SEM of male antenna.

Figure 16. Habitus and character photos of Euconnus cultellus A male, dorsal view B female, dorsal view C SEM of male antenna.