Euconnus, Thomson

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 : 387-388

4. Preliminary identification key to subgenera of Euconnus (and the ‘ Tetramelus problem’)

The subgeneric division of Euconnus , or even limits of the genus, are still problematic. The Malagasy Madagassoconnus seems to be derived from the continental African Tetramelus , and Oneila may only be a species group within Tetramelus . The endemic New Caledonian Austroconophron seems to be a good candidate to merge with Euconnus s. str., as it does not have any peculiar characters to maintain it as a separate subgenus. New intermediate forms may be found and some of the existing subgenera may require merging into one. Some subgenera are defined mainly or exclusively by male dimorphic features and females cannot be placed to subgenus. Such subgenera may in fact represent species groups derived from within Euconnus s. str. Moreover, some described species of Euconnus not placed to subgenus show a unique set of features that may justify proposing a new subgenus, e.g. a large group of Sri Lankan species including and similar to E. mutabilis Franz, 1982 . Such species in the key would very likely go to Euconnus s. str. For these reasons, the key should be treated as a summary of the hitherto made changes in the classification of Euconnus , pending further study. The same key with illustrated morphological structures is given in Figs 115–117 .

The key, already in its current form, has a serious flaw. Euconnus kraatzi , previously placed in Psomophus , and now in Euconnus s. str., has the pronotum broadest clearly in front of middle. This species is not possible to place to subgenus using the key presented below, and there may be more similar Euconnus spp. Euconnus kraatzi seems to be an intermediate form between Euconnus s. str. and the subgenus Tetramelus , and in future these subgenera may be merged. The European Tetramelus species are wingless, and consequently they have reduced humeral structures of the elytra. Their antennal clubs are either gradually thickened or with tetramerous clubs, and their pronotal structures and mouthparts are relatively diverse (e.g., Orousset 2015). Outside Europe, especially in Africa and Australia, there are species that are highly similar to the European Tetramelus but winged, and therefore the silhouette of their elytra is clearly different, because the humeral calli are strongly developed. Tetramelus may only be a group (or several unrelated groups) within Euconnus s. str. This problem requires further study, preferably by molecular methods. Although I prefer in the present study not to go as far as merging Tetramelus with Euconnus s. str. (even though there are firm morphological reasons), the fact that it was impossible to construct a key to subgenera that would not allow for exceptions (as E. kraatzi ) clearly demonstrates that the subgeneric system of Euconnus is still impractical and very likely does not reflect phylogenetic relationships. It is presented nevertheless, as a starting point for future work.

There is another reason to publish a ‘flawed’ key. Most of the problematic species, as E. kraatzi , would be impossible to key out, and when such a case is encountered, it may mean that the species in question is particularly interesting. For instance, it may show some intermediate or unusual characters. Such species may in fact prove to be indispensable for further study of Euconnus , one of the largest genera of any organisms on Earth. The key below can help identifying such interesting, problematic species, and this is one of its intended functions.

1 Hypostomal ridges running behind posterior submental margin as single transverse carina [ Madagascar]. Nodoconnus Franz

- Hypostomal ridges running posteromesad................................................................. 2

2 Head ventrally with longitudinal gular groove; vertex with step-wise posterior narrowing (in some species indistinct) [Central and South America]................................................................. Rhomboconnus Franz

- Gular groove lacking; vertex posteriorly not step-wise narrowed................................................ 3

3 Sides of pronotum with longitudinal hypomeral groove [ Madagascar]...................... Glabriconnus Jałoszyński

- Hypomeral grooves lacking............................................................................. 4

4 Pronotum broadest in front of middle..................................................................... 5

- Pronotum broadest at middle, behind middle or with sides parallel in posterior half................................. 8

5 Antenna in male unmodified, gradually thickened or with variously distinct tetramerous club......................... 6

- Antenna in male modified.............................................................................. 7

6 Tarsomere 4 in all legs with long distoventral lobe [ Madagascar]........................... Madagassoconnus Franz

- Tarsomere 4 lacking long distoventral lobe [worldwide].................................. Tetramelus Motschulsky

7 Male antennomeres 8‒9 with longitudinal microserrate mesal ridges; pronotal base with 6 pits and median longitudinal carina [Palaearctic]......................................................................... Cladoconnus Reitter

- 1‒3 middle antennomeres in males enlarged and asymmetrical; pronotal base with 4 pits and lacking median carina [ South Africa] ................................................................................ Oneila Peringuey

8 Antennal club in males trimerous AND distinctly modified, with at least antennomere 9 asymmetrical [Borneo]............................................................................................. Borneoconnus Franz

- Antennal club in males either not trimerous, or, if clearly trimerous, lacking asymmetrically modified antennomeres...... 9

9 In males, antennae gradually thickened and antennomeres 9‒11 (in some species 9 indistinctly) modified, with asymmetrical impressions and projections [Central and South America]..................................... Androconnus Franz

- In males, antennae either with clearly delimited club or gradually thickeningAND antennomeres 10 and 11 lacking asymmetrical modifications....................................................................................... 10

10 Pronotum broadest at middle and similarly narrowing posterad and anterad, lacking any antebasal structures AND antennae in both sexes gradually thickening [ New Caledonia]....... Austroconophron Franz [possibly identical with Euconnus s. str.]

- Pronotum of various shapes, but rarely as above, if equally narrowing anterad and posterad and lacking antebasal pits, grooves and carinae, then antenna with club [worldwide]............................................... Euconnus s. str.

Figures

FIGURE 115. Illustrated key to subgenera of Euconnus, part 1.

FIGURE 116. Illustrated key to subgenera of Euconnus, part 2.

FIGURE 117. Illustrated key to subgenera of Euconnus, part 3.