Belonuchus optatus ( Sharp, 1885 )

Márquez, Juan & Asiain, Julieta, 2022, Taxonomy of the Mexican species of Belonuchus Nordmann (Coleoptera: Staphylinidae), Zootaxa 5152 (1), pp. 1-129 : 81-82

Belonuchus optatus ( Sharp, 1885)

Figs. 8c , 10g, j , 16o , 20g , 24k , 27b

Philonthus optatus Sharp, 1885: 427 . Belonuchus optatus comb. nov. ex Philonthus ( Chani-Posse et al. 2018b) .

Total body length 10.9 mm. Black on head, antennae, pronotum, scutellum, posterior 2/3 (or slightly less) of fifth visible abdominal segment, sixth visible segment and abdominal styli. Reddish on elytra, legs, visible abdominal segments 1–4 and anterior 1/3 (or slightly more) of fifth visible segment. Reddish-brown on two apical antennomeres, maxillary and labial palpi, anterior half of mesoventrite and entire metaventrite.

Head ( Fig. 10j ): subquadrate shape; ratio length/width 0.93. Dorsal surface with microsculpture like wavy lines moderately visible; punctures denser than in majority of species, distributed mainly in posterior 2/3 of head; sulcate longitudinal midline faintly visible from anterior margin to posterior 2/3 of head; front moderately foveate between antennal insertions and slightly posteriorly. Eyes small, nearly 0.4 times the cephalic lateral length, not protruding laterally. Antennomere 4 elongate, 5 as long as wide, 6–10 transverse. Mandibles probably shorter than head (they are broken at apex and closed), each with a middle tooth and possibly with a basal tooth separated from middle tooth; mandibular channel well developed, external and internal margins well separated at base, both carinate, internal margin extending forward like impressed line. Apical palpomere of maxillary palpi 1.4 times longer than preapical palpomere.Apical palpomere of labial palpi almost as long as preapical palpomere. Head 1.08 times wider than pronotum. Ventral surface with microsculpture as on dorsal surface and with very sparse, fine punctures.

Thorax: pronotum ( Fig. 10j ) 1.19 times longer than wide; almost as wide at anterior corners as at posterior corners (1.06 times); left dorsal row with seven punctures and right dorsal row with eight punctures, dorsal rows occupying slightly more than 3/4 of pronotal length. Scutellum with punctures denser than on elytra, latter with moderately dense punctation. Prosternum slightly elevated transversally near anterior margin, but without constriction separating this area from remaining portion. Intercoxal process of mesoventrite oblong shield-shaped with acute apex; transverse discal ridge U-shaped, not meeting margin of intercoxal process laterally, but very close to it. Legs without visible modifications (as in many females of this genus). Tarsomeres weakly flattened dorsally.

Abdomen: visible tergites 1–3 with indistinct posterior basal transverse carina; adjacent depressed area conspicuous and somewhat deep, with sparse wide-superficial punctures combined with some fine punctures, remaining surface of these tergites, as well as remaining tergites, only with sparse, fine punctures. First visible sternite with posterior basal transverse carina more separated from anterior margin than in sternites 2–3, visible sternites 4–6 without posterior basal transverse carina; sternites 1–4 with apical portion slightly depressed and with some wide-superficial punctures combined with fine punctures, which cover also the rest of the surface and remaining sternites.

Variability. Male with total body length 10.4 mm; head ( Fig. 10g ) slighly convex dorsally, almost as long as wide (ratio 0.94); posterior corners with wavy roughness, appearing as a faint carina; mandibles shorter than head (ratio 0.84); head 1.16 times wider than pronotum; left dorsal row of pronotum with six punctures and right dorsal row with eight punctures, rows extending on major portion of pronotal length; pronotum 1.25 times longer than wide and almost as wide at anterior corners as at posterior corners; scutellum black, with punctures slightly denser than on elytra, latter with moderately dense punctation; intercoxal process of mesoventrite dark, shield-shaped; transverse discal ridge broadly U-shaped, slightly crenulate; profemur with row of small and sparse spines at external margin; metatrochanter small, with acute apex, with similar shape as in B. aenigmaticus or as in very small males of B. apiciventris ; metafemur and metatibia straight; abdominal segments with sparse wide-superficial punctures and fine punctures; pregenital sternite ( Fig. 16–o ) with moderate U-shaped emargination at posterior margin, emargination with membranous extension making it difficult to see; genital sternite short (2.3 times longer than wide), weakly asymmetrical, anterior portion occupying 26% and posterior portion 74% of its length, apical emargination deep ( Fig. 20g ). Abdominal styli slender. Aedeagus 1.25 mm long; cone-shaped, with acute apex, sides becoming gradually wider toward base, which is notably wider than apical half; internal sac little visible ( Fig. 24k ).

Taxonomic comments. Belonuchus optatus is known only from the partly damaged female holotype, and one non-type male. Two characters allow us to consider it as a valid species for now: the high density of punctures on the dorsal surface of the head ( Fig. 10g ) and also the large number of punctures in the dorsal rows of the pronotum ( Fig. 10j ): seven on the left and eight on the right that are distributed almost throughout its length. These characters allowed us to propose that one male specimen from the semiarid zone of Querétaro (near the state of Guanajuato) is the second known specimen of this species, which has a trochanter of the posterior legs similar to those of B. aenigmaticus (with only an acute apical spine). Therfore, it was decided to place this species in the platypterus group. It is still necessary, however, to have more specimens to ensure both their identity as valid species and their placement in this group. This species is very similar to B. aenigmaticus , and the characters to distinguish them are located in the taxonomic comments of the latter species, as well as comments on the placement of this pair of species in the platypterus group.

Type material examined: Holotype (female, NHM): “ Philonthus optatus Type D.S. Guanajuato. Mexico. Sallé / Type / Guanajuato / Mexico. Salle Coll. / B. C. A. Col. I. 2. Philonthus optatus, Sharp / Belonuchus formosus apud Sallé ”. Additional material examined (one male): Mexico: Querétaro: “ Peñamiller, Maguey Verde, 2190 m, necrotrampa, 5 a 10-VIII-2002, Q. Santiago y L. Delgado cols.” (m 1, IEXA) .

Figures

FIGURE 8. Dorsal view of males of: a) Belonuchus aenigmaticus (paratype), b) B. nigerrimus, c) B. optatus, d) B. platypterus, e) B. juanmorronei, f) B. abnormalis, g) B. pectinipes (paralectotype), h) B. viridipennis. Scale bars = 2.5 mm.

FIGURE 10. Dorsal view of the head of males of: a) Belonuchus julietitae, b) B. singularis, c) B. connexus, d) B. platypterus, e) B. bidens, f) B. nigerrimus, g) B. optatus, h) B. cyanipennis, i) B. godmani. Dorsal view of the head and pronotum of the holotype female of: j) B. optatus.

FIGURE 16. Male pregenital sternite of: a) Belonuchus moroni, b) B. dichrous, c) B. flavipennis, d) B. aenigmaticus, e) B. nigerrimus, f) B. juanmorronei, g) B. godmani, h) B. magnistylus, i) B. trochanterinus, j) B. rufipennis, k) B. basiventris, l) B. connexus, m) B. xanthomelas, n) B. ephippiatus, o) B. optatus.

FIGURE 20. Male genital sternite of: a) Belonuchus cifuentesi, b) B. dichrous, c) B. flavipennis, d) B. aenigmaticus, e) B. iridescens, f) B. nigerrimus, g) B. optatus, h) B. platypterus, i) B. juanmorronei, j) B. abnormalis, k) B. pectinipes, l) B. viridipennis, m) Belonuchus sp. Q, n) B. cyanipennis, o) B. godmani. Scale bars = 0.5 mm.

FIGURE 24. Ventral (left) and lateral (right) view (except e) of the aedeagus of: a) Belonuchus rufiventris, b) B. xanthomelas (at center, detail of the apex of the median lobe), c) B. ephippiatus, d) B. moroni, e) B. cifuentesi (left: detail of paramere, right: ventral view; from Rodríguez and Navarrete-Heredia, 2016), f) B. dichrous, g) B. flavipennis, h) B. aenigmaticus, i) B. iridescens, j) B. nigerrimus, k) B. optatus, l) B. platypterus. Scale bar = 0.5 mm (all figures, except e).

FIGURE 27. Geographical distribution in Mexico of: a) Belonuchus erichsoni and B. oxyporinus; b) B. longitarsus, B. metafemoralis, B. mixtecus, B. optatus and B. rufiventris.