Paraxenopygus Bernhauer 1911
Creators: name: Chatzimanolis, Stylianos
name: Brunke, Adam J.
name: Navarrete-Heredia, José L.
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Staphylinidae
Paraxenopygus

description: Paraxenopygus Bernhauer, 1911
(Figures 1–6)
Type species
Paraxenopygus tremolerasi Bernhauer, 1911, fixed by monotypy.
Species included
Paraxenopygus maurocyanos, P. newtoni, P. opacipennis, P. peruvianus and P. tremolerasi.
Diagnosis
Paraxenopygus can be distinguished from all other Xanthopygina genera based on the combination of the following characteristics: head transverse with anterior margin of head shorter than posterior margin (except P. opacipennis); head and pronotum not densely setose (Figure 2A–E) as in some species of Glenus Kraatz (Figure 3H) and Tricholinus pehlkei Bernhauer; eyes small (eyes less than half of head length), elongate and positioned laterad; antennal fossa transverse; antennomeres 6–10 transverse and slightly compressed; mandibles straight (except P. tremolerasi) and narrow; right mandible with single tooth; maxillary palpomere 4 longer than palpomere 3 (Figure 3F); labial palpomere 3 not dilated, parallel-sided; pronotum quadrate and convex (lateral margins of pronotum weakly sinuate in P. newtoni and P. peruvianus); pronotal hypomeron with superior marginal line continuous to anterior margin; pronotum without postcoxal process; protibia slightly dilated apically; tibia not flattened (as in Scariphaeus Erichson); hind coxa with coxal shield (more developed in males); and in males, sternite 7 with porose structure (Figure 4A–E).
Paraxenopygus is morphologically most similar to Glenus and Tricholinus. While Tricholinus and the species of Glenus with densely setose head and/or pronotum can be readily distinguished from Paraxenopygus, some other species of Glenus (eg Glenus coxalis Sharp) are strikingly similar to Paraxenopygus at first glance. However, there are two characters that can readily distinguish Paraxenopygus from all Glenus: the eyes and the last maxillary palpomere. In Glenus, the eyes are smaller than in Paraxenopygus, about as long as wide, and shifted dorsad (Figure 2A –Evs F–H). The dorsal position in Glenus can be visualised as the outer eye margin pulling away from the lateral margin of the head. In Paraxenopygus, the last maxillary palpomere (Figure 3F) is longer than the penultimate palpomere, while in Glenus the last maxillary palpomere is shorter (Figure 3H) than or in a few cases subequal (Figure 3G) to the penultimate palpomere. In addition to these two consistent characters, many species in Glenus (but not all) have the pronotum longer than wide (Figure 2H) with sinuate (Figure 2H) or explanate (Figure 2G) margins, while the pronotum is always quadrate and convex in Paraxenopygus, and the margins are never sinuate or explanate (Figure 2A–E). Finally, Glenus have circular or transverse antennal fossa, while all Paraxenopygus have transverse antennal fossa.
Description
Habitus as in Figure 1. Body medium-sized, forebody 6.1–8.5 mm, with long bristle-like setae (but not as many as in Haematodes Laporte). Head transverse with anterior margin of head shorter than posterior margin (except in some specimens of P. opacipennis); head of males typically larger than that of females (see Discussion); head shorter than pronotum. Eyes small (less than 1/2 length of head). Postclypeus, in comparison to frons, not deflexed; anterior margin convex. Middle of epicranium with continuous punctures. Postmandibular ridge present laterally; without punctures demarcating raised postmandibular ridge. Gular sutures not joined before neck, extended close to each other at base of head capsule. Nuchal ridge complete dorsally. Neck disk with dense, moderately coarse to fine punctures.
Antennae (Figure 4F–G) with antennomere 1 equal or slightly wider than 2; antennomere 3 2.5 times as long as wide or less; antennomere 4 without tomentose pubescence; antennomere 5 with tomentose pubescence present (except P. tremolerasi); antennomeres 4–10 cylindrical in shape; antennomeres 5–10 without club; antennomeres 1–3 longer than wide; antennomere 4 subquadrate to transverse; antennomeres 5–10 symmetrical, transverse and slightly compressed; antennomere 11 in males slightly longer than 10.
Mouthparts with labrum having broadly U-shaped emargination, lobes strongly separated. Mandibles with relative length typical (ie closed mandible not extending beyond lateral margin of head); without asymmetrical torsion. Mandibles in dorsal view straight and narrow (but see description of P. tremolerasi below); in lateral view slightly bent downwards anteriorly; left mandible and right mandible with one tooth. Maxilla with galea subequal to palpus; maxillary palpus with palpomere 3 shorter than 2; palpomere 4 longer than 3; palpomere 4 not dilated. Labial palpus with palpomere 3 widest before apex; palpomere 3 without long dense setae on entire lateral sides. Ligula small, entire. Mentum with alpha seta present; hypostomal cavity present; moderately delimited.
Pronotum quadrate, with lateral margins in dorsal view posteriad of midpoint rounded; anterior angles in dorsal view not strongly acuminate and produced laterad. Pronotum near anterolateral angles without raised impunctate spots; anterolateral corners with punctation; disc of pronotum with punctation beyond midlength; punctation pattern varying from loose rows on either side of impunctate midline to irregularly punctate on either side of impunctate midline; with sparse micropunctures and transverse lines of microsculpture; without coarse punctures impressed in flange at posterior angle of pronotum. Hypomeron with superior marginal line continuous to anterior margin; inferior marginal line of hypomeron continued as separate entity beyond anterior pronotal angles and curving around them. Superior and inferior marginal lines produced as anterolateral angles parallel to one another. Postcoxal process absent. Basisternum slightly longer than furcasternum; basisternum with pair of macrosetae, situated far from anterior margin of prosternum.
Elytra not reduced; hindwings present. Elytra setae not reduced, easily seen at low magnification; without patches of white setae. Elytra with contiguous polygon-shaped meshed microsculpture but density varies among different species. Mesoscutellum with dense cluster of punctures medially.
Legs with tarsi 5-5-5; prefemora without lateroventral apical spines; protarsi with modified pale (tenent) setae ventrally; protibia with long series of spurs laterally and with small apical ctenidium; protarsi with tarsomeres 1–4 dorsoventrally flattened. Mesocoxae strongly separated, intercoxal area on approximately same plane as both meso and metaventrital processes. Mesotarsi without tenent setae. Metacoxae with coxal shield, coxal shield varies among species. Metatibia with thick and long apical spurs (spurs longer than 3/4 legth of tarsomere 1); with spines. Meso/metatarsi without asymmetrically lobed tarsomeres 1–4; tarsomeres 3–5 of metatarsi with dorsal surface of tarsomeres glabrous along midline. Pretarsal claws with empodial setae.
Abdomen with lateral sides in dorsal view more or less parallel-sided; protergal glands with well-developed acetabula. Anterior basal transverse carina on tergites 3 and 4 without pair of accessory ridges; tergite 3 without posterior basal transverse carina; tergites 3–4 with curved carina (arch-like) on some species; centre of tergite 5 with punctation; posterior half of tergite 5 in lateral view not appearing bulging. Sternite 3 with straight to arcuate basal transverse carina medially; basal transverse carina laterally not sinuate. Sternite 4 without basal transverse carina medially. Sternite 5 with dense, meshed microsculpture anterolaterally, appearing different in texture to posterior portion. Males with porose structure on sternite 7 and medial emargination on sternite 8. Aedeagus with long median lobe and single paramere; paramere with sensory peg setae; endophallus prominent. Spermatheca not sclerotised.
Habitat
Paraxenopygus lives in low- to mid-elevation tropical rainforests in the refuse piles of Acromyrmex spp. and it is thought to be an obligate associate of these ants (Navarrete-Heredia 2001; and specimen records listed below). There are specimen records indicating that some species may be associated with Atta spp. as well, but whether the ants were misidentified or Paraxenopygus is indeed associated with two different genera of Attini ants is still unclear.
description: Published as part of Chatzimanolis, Stylianos, Brunke, Adam J. & Navarrete-Heredia, José L., 2024, A review of Paraxenopygus Bernhauer (Insecta: Coleoptera: Staphylinidae), with description of two new species, pp. 1509-1528 in Journal of Natural History 58 (37 - 40) on pages 1511-1517, DOI: 10.1080/00222933.2024.2391450, http://zenodo.org/record/13758597