Scydmaenus (Ascydmaenus) Jałoszyński 2023, subgen. n.
Creators: name: Jałoszyński, Paweł
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Staphylinidae
Scydmaenus

description: Subgenus Ascydmaenus subgen. n.
Type species: Scydmaenus subglabratus sp. n. (here designated).
Diagnosis. Scydmaenus with the following set of characters: (1) antenna with trimerous and weakly delimited club, unmodified in males (Fig. 171); (2) submentum with massive subrectangular lateral lobes projecting anteriorly and partly overlapping with mentum (Fig. 168); (3) pronotum lacking antebasal pits (Fig. 163); (4) elytra lacking basal foveae (Fig. 163); (5) basisternal region of prosternum subequal in length to procoxal rests (Fig. 164); (6) mesoventral intermesocoxal process narrowly carinate (Fig. 169); (7) metanepisterna completely fused with metaventrite (Fig. 169); (8) metaventral intermetacoxal process conspicuously narrow, only about as wide as 1/4 width of posterior metaventrite (excluding metanepisterna) and about half width of one metacoxa (Fig. 169); (9) aedeagus in dorsal view narrowing from sub-basal region, with minute setae on apical margin, with proximal region of flagellum symmetrically expanded to form vesicular structure indistinctly divided into three compartments (Fig. 176); and (10) males with each profemur bearing tooth-like projection on ventral distal region (Fig. 182).
Description. Body conspicuously stout and convex (Figs 171–173).
Head (Figs 163–165) small in relation to pronotum, subhexagonal to rounded; frons and vertex confluent, posterior margin of vertex nearly straight, anterior margin of frons between antennal insertions subtrapezoidal, weakly convex anteriorly; labrum (Fig. 166) with deep median rounded emargination; submentum (Fig. 168) with conspicuously large lateral lobes, each subrectangular and projecting anteriorly to near middle of mentum, so that only median 1/3 of mentum in its proximal half is visible between lobes; hypostomal ridges (Fig. 168) not connected at middle; gular plate (Fig. 164) lacking anteromedian projection; anterior exposed portion of head capsule demarcated from neck region by narrow impression; occipital constriction (Figs 163, 182) variable in width, from distinctly wider to slightly narrower than half width of head.
Antennae (Figs 171, 182) long and slender, with weakly delimited trimerous clubs; antennomeres 7 and 8 nearly symmetrical.
Pronotum (Fig. 163) massive, with anterior and lateral margins rounded together, so that anterior corners are not marked; posterior corners distinct, slightly projecting posteriorly; posterior margin straight or weakly arcuate. Pronotal base with short but distinct posterior marginal carina (Fig. 163), lacking pits and longitudinal carina.
Ventrally, prothorax (Fig. 164) with broad hypomera, somewhat indistinct hypomeral ridges connected in front of procoxal rests to form anteprocoxal carina; basisternal region of prosternum about as long as procoxal rests; notosternal sutures vestigial, marked as pair of short notches at ventral anterolateral regions of prothorax.
Elytra (Figs 163, 165, 171–173, 182) conspicuously stout, lacking basal foveae, and lacking or with barely discernible basal impressions; humeri angulate.
Mesoventrite (Fig. 169) with large concave procoxal rests on massive prepectus, rests separated at middle by low median longitudinal ridge posteriorly separated from mesoventral process; lateral regions of prepectus projecting laterally, forming rounded subtriangular convexities. Mesoventral intermesocoxal process narrowly carinate, posteriorly fused with anterior metaventral process, fusion site marked on surface by shallow transverse fissure.
Metaventrite (Fig. 169) with narrow and strongly elongate anterior metaventral process, behind mesocoxal projections with posteriorly converging short lateral carinae; laterally metaventrite completely fused with broad metanepisterna; metaventral intermetacoxal process as narrow as about 1/4 of width of posterior metaventrite (excluding metanepisterna) and only as wide as about half width of one metacoxa, posterior margin of metaventral process deeply emarginate.
Abdomen (Fig. 169) with six exposed sternites (III–VIII), sternite III distinctly longer than each of IV–VII but shorter than VIII, with narrow subtriangular anteromedian projection fitting into emargination of metaventral process; metacoxal rests with carinate posterior margins. Elytral locking device on abdominal tergite VIII (Fig. 170) with median longitudinal impression distinctly narrowing posteriorly and flanked by large microtrichial fields; pygidium (Fig. 170) subvertical, subtriangular with rounded posteroventral margin.
Legs (Figs 164–165, 169, 171–173, 182) robust, with generalized structures typical of Scydmaenus.
Sexual dimorphism. Males with distoventral tooth-like projection on each profemur; protibiae slightly to strongly thickened; protarsi with tarsomeres 1–3 slightly to distinctly broadened, with ventral tenent setae sparse, obscured by unmodified setae.
Aedeagus (Figs 174–181, 183–186) with median lobe in dorsal view narrowing from sub-basal region toward apex, with sinuate lateral margins, apex rounded and indistinctly notched at middle, with minute lateral setae; in lateral view median lobe bent, but with distal region not broadened; ostium situated in distal 1/3 of median lobe; proximal region of flagellum with symmetrical vesicular broadening indistinctly divided into three compartments.
Etymology. The name Ascydmaenus is a negation of Scydmaenus; gender masculine.
Distribution and composition. Two included nominal species are endemic to continental Australia: S. haigensis sp. n. and S. subglabratus sp. n. In addition, three species similar to S. subglabratus sp. n. were seen, each represented by a single female, all from Queensland (from Mt. Spec, Lamington Plateau, and the summit of Mt. Abbot; QM).
Remarks. Besides the characters listed in the diagnosis, adults of Ascydmaenus are characteristically stout and strongly convex, not resembling a ‘typical’ Scydmaenus (the most typical or most commonly found body form in this genus is that of the European S. tarsatus Müller & Kunze, 1822, with slenderer and stouter variants). Only some species currently placed in Armatoscydmaenus and the Malagasy species of Trapezoscydmaenus are strikingly different from a ‘typical’ Scydmaenus, although they do not closely resemble Ascydmaenus in the body form. Armatoscydmaenus (which is a candidate for a junior synonym of Scydmaenus s. str.; Jałoszyński, unpublished obs.) has the antebasal pronotal pits, the metanepisterna fully demarcated from the metaventrite, and the metafemora of males modified, with a ventral tooth-like projections (none of these characters occurs in Ascydmaenus). Trapezoscydmaenus (both the northern African type species of the subgenus and the disjunctive group of Malagasy species) has a conspicuously short prosternum with the basisternal region shorter than procoxal rests, the pronotum with dense posterolateral patches of setae directed posteriorly, the elytral base deeply impressed at middle just behind the mesoscutellar shield, and metanepisterna fully separated from the metaventrite—none of these features can be found in Ascydmaenus. Interestingly, Ascydmaenus and the Malagasy species of Trapezoscydmaenus are the only subgenera with relatively narrowly separated metacoxae, because of the metaventral process being only as broad as about 1/4 width of the metaventrite (excluding metanepisterna). The mesoventral process is also similarly narrow in these subgenera. The submental lobes (present in Ascydmaenus and absent in Trapezoscydmaenus) and the metanepisterna (fused with the metaventrite in Ascydmaenus vs. demarcated in Trapezoscydmaenus) unambiguously differentiate these taxa.
The lateral submental lobes, that is, a pair of plates on the anterior margin of the submentum projecting anteriorly and partly overlapping with the mentum, so strongly developed in Ascydmaenus, among other subgenera of Scydmaenus can be found only in Mascarensia (Fig. 97). In at least some species of various subgenera, including e.g., Parallomicrus and Scottiscydmaenus, the anterolateral corners of the submentum are strongly projecting anteriorly and subtriangular, but they do not overlap so strongly with the mentum, and the latter structure is almost entirely exposed, not hidden under the lobes, as in Ascydmaenus and Mascarensia. Ascydmaenus clearly differs from Mascarensia in the metanepisterna fused with the metaventrite (separated in Mascarensia), the narrow metaventral intermetacoxal process (wide in Mascarensia), and in a narrowly carinate mesoventral intermesocoxal process (broad, subrectangular in Mascarensia).
Scottiscydmaenus, whose males also have profemoral teeth (either one large in the distal region, as in the Australian species, or a row of teeth on the entire length, as in the type species of the subgenus) share with Ascydmaenus the fused metanepisterna and lack of pronotal pits and elytral foveae. However, the profemoral teeth in Scottiscydmaenus and Ascydmaenus are not homologous. In Scottiscydmaenus, the teeth are developed on the anterior, or dorsal longitudinal carina that demarcates the ventral concavity where the tibia fits when it is fully flexed (Fig. 129). In Ascydmaenus, a similar elongate impression bordered by longitudinal ridges is developed on the ventral surface of the profemora (as in most species of Scydmaenus and many other beetles), but in males the profemoral tooth is developed not on the anterior (dorsal), but on the posterior (or ventral) ridge. The ventral/dorsal terminology refers here to the orientation of the fore leg as in Fig. 130 (where the profemoral tooth is dorsal) and in Fig. 182 (where the tooth is ventral). Moreover, in Scottiscydmaenus the mesoventral intermesocoxal process is subrectangular, not carinate, with distinctly flat and setose ventral surface (vs. narrowly carinate, keel-like in Ascydmaenus), and the metacoxae are broadly separated by the metaventral process about as wide as 1/3 of the posterior metaventrite and about as wide as or even wider than one metacoxa.
Identification key to species of Scydmaenus (Ascydmaenus)
1 BL <2 mm; dorsum nearly asetose; elytral base much broader than pronotal base; in male profemoral tooth minute, broad and short...................................................................... Scydmaenus subglabratus sp. n.
- BL> 2.4 mm; dorsum densely setose; elytral base indistinctly broader than pronotal base; in male profemoral tooth prominent, nearly as long as broad......................................................... Scydmaenus haigensis sp. n.
description: Published as part of Jałoszyński, Paweł, 2023, Scydmaenus Latreille of Australia: Revision of species in subgenera Choleropsis Franz, Kingius Franz, Mascarensia Franz, Parallomicrus Franz, Scottiscydmaenus Franz, and description of Ascydmaenus subgen. n. (Coleoptera, Staphylinidae, Scydmaeninae), pp. 1-75 in Zootaxa 5371 (1) on pages 62-64, DOI: 10.11646/zootaxa.5371.1.1, http://zenodo.org/record/10144644