Rhyparus pteronellus Skelley and Smith, 2024

Rhyparus pteronellus Skelley and Smith , new species

Figures 30–39 View Figures 30–34 View Figures 35–40 , 41 View Figure 41

Diagnosis. Although the Western Hemisphere members of Rhyparus need revisionary work, R. pteronellus is the only known Western Hemisphere species that has a greatly reduced or completely lacking medial part of the discomedian costa on the elytra. This costa is variably developed in other species but usually distinct (except in some specimens of R. hexadentatus , where it is weakly evident). Other characters of note are the robust body, weak discolateral impressions on the metaventrite, reduced flight wings, reduced eyes, and distinct male genitalia with elongate parameres. The only other Western Hemisphere rhyparines known with reduced eyes and wings are in the genus Nanotermitodius Howden ( Skelley et al. 2022b; Howden 2023) in Oaxaca, Mexico. Rhyparus pteronellus is only known from the type locality in Chiapas, Mexico.

Description. Holotype male ( Fig. 30–32 View Figures 30–34 ). Body length 3.6 mm, width 1.3 mm. Dorsum dark red-brown to black with head, pronotal lobes, and legs tinged with brown; elongate, almost parallel-sided.

Head. Head one-third wider than long, surface smooth with coarse punctures bearing a short seta ( Fig. 33 View Figures 30–34 ); clypeus anteriorly with inflexed, very slightly concave margin, lower edge medially sharply, obtusely angulate, with short setal fringe, upper edge of inflexed margin slightly quadridentate, inner obtuse tooth on each side at lateral third, outer tooth on each side adjacent to gena; clypeal disc defined anteriorly by U-shaped groove (peridiscal impression), and posteriorly by arcuate suture, enclosed area broadly conical with central transverse tubercles obsolete. Vertex with four short longitudinal costae, two frontodiscal costae slightly closer and with deep groove between. Gena anteriorly lobed, posteriorly depressed above eye, eye reduced ( Fig. 37 View Figures 35–40 , compare with Fig. 40 View Figures 35–40 ), not visible dorsally.

Pronotum. Pronotal width = length, with six irregularly longitudinal costae bearing rows of fine setae; paramedian costa complete, sinuate, slightly convergent in anterior half, surface between with few coarse punctures anteriorly and two small foveae posteriorly on glossy surface; discolateral costa interrupted in anterior third by deep irregular pits, costa anterior to pits similarly and slightly wider than posterior part; submarginal costa on each side distinctly outwardly sinuate near middle with adjacent deep, mesad depression; all costae extending to posterior pronotal margin; lateral margin of pronotum with two lobes, equally developed, subtriangular; posterior third obsolete; posterior angle reduced and hidden under posterior part of submarginal costa; lateral posterior margins lacking disjunct marginal bead.

Scutellum. Scutellar shield minute, narrow, apex acute.

Elytra. Elytron with four sharply elevated costae bearing rows of fine setae ( Fig. 33 View Figures 30–34 ); discomedian costa lacking along midline, separated from juxtasutural costa by double row of large, deep punctures, posterior part of costa gradually widening to trichome; discolateral costa more elevated, strongly sinuate, highest on posterior part where it abruptly turns inward to trichome, separated from discomedian costa by double row of large punctures basally and apically with single very large puncture row at middle; posthumeral costa sharply elevated at basal quarter, then almost disappearing at basal fifth, where starts again gradually decreasing in size to caudal trichome, costa separated from discolateral costa by double row of transverse punctures; submarginal costa fine, straight, swelling posteriorly as separate lobe next to and part of caudal bulb, costa separated from posthumeral costa by double row of coalescing coarse punctures.

Flight wings. Metathoracic wings greatly reduced to narrow band, mostly consisting of remnant costal veins ( Fig. 34 View Figures 30–34 ), flightless, elytra fused.

Ventral thorax. Prosternal apophysis anteriorly broadly lanceolate; posterior prosternal apophysis hastate. Mesoventrite short, surface finely densely punctate, median surface flattened. Metaventrite not shortened, length between mesocoxae and metacoxae equal to length of metacoxa; anterior metasternal projection separating mesocoxae; elongate median impression occupying over half of length; two small anterolateral juxtacoxal impressions, with discal depressions weak and obscured in coarse punctation.

Abdomen. Abdomen with five ventrites; first four ventrites narrow, slightly wider laterally; basal ventrite medially with oval concavity, all four basal ventrites with small depression on each side near lateral edge, and deep, coarsely punctate grooves at base; apical ventrite approximately as long as adjacent three ventrites combined, basal third a deep transverse foveate depression each side of median ridge; apical two-thirds of ventrite convex, surface coarsely punctate, punctures bearing a recumbent seta. Pygidium flattened, apical three-fourths outlined by distinct ridge, basal portion above ridge finely setose with distinct median longitudinal sulcus; posterior to sulcus a three-part flattened area outlined by fine carinae (two large lateral regions and a median basal triangle, Fig. 36 View Figures 35–40 ), surface near posterior margin finely punctate, rest of surface glossy; apex of pygidium rounded.

Legs. Ventral surfaces of all femora irregularly punctate-setose; profemur robust; mesofemur elongate with curved anterior margin; metafemur narrowed most of length; all femora with a well-defined margin for reception of tibia. Protibia with broad apex bidentate, one tooth anteromedial and one anterolateral. Mesotibia and metatibia similarly developed, gradually widening to truncate apex; inner apical margin weakly sinuate, with distinct, inwardly projecting tooth at apex; apical margin with short, complete fringe of spinules. Mesotarsus and metatarsus about half as long as respective tibia; tarsomere 1 half as long as tarsus.

Genitalia ( Fig. 37–38 View Figures 35–40 ). Male genitalia slender, tubular, gradually curved; phallobase two times longer than parameres; parameres elongate, rounded apically.

Allotype female. Length 3.3 mm, width 1.3 mm. Similar to male, showing dimorphism in mesotibia and metatibia lacking apical tooth.

Variation. Length 3.3–3.9 mm, width 1.3–1.6 mm. The punctures in the middle of the elytral disc where the discomedian costa is interrupted vary in number and arrangement. No other notable variation was observed.

Material examined. Holotype male and allotype female in CMNC: “ MEXICO: Chiapas, Volcan / Tacana , lower slopes, ca. 4km. / N. Union Juarez, 2000m, 19.IX. / 1992, R. S. Anderson, 92-110 / cloud forest litter” . Holotype with additional red label”/ HOLOTYPE ♂ / Rhyparus / pteronellus / des. 2024 / Skelley & Smith” . Allotype with blue label stating “ ALLOTYPE ♀ ”.

Paratypes (9): Same data as holotype (2 CMNC) ; same data as holotype except “… 20.IX. / 1992, R. S. Anderson, 92-111 / cloud forest litter” (1 CMNC, 4 FSCA, 2 IEXA) .

Etymology. The species epithet was derived by intentionally combining the Greek word for wing “ pteron ” with a Latin suffix “- ellus ”, denoting small, diminutive wings.

Comments. Mora-Aguilar and Delgado (2019) reviewed the species of Rhyparus occurring in Mexico and Guatemala. Following the key in Cartwright and Woodruff (1969), R. pteronellus will fall to the species with two puncture rows in all intervals, which would lead us to R. opacus Cartwright and Woodruff and R. spangleri Cartwright and Woodruff , a group that also now includes R. chimalapensis Mora-Aguilar and Delgado. However , the loss of the discomedian costa along the midline and the distinct impressions of the metaventrite readily separate R. pteronellus from these and all other regional Rhyparus .

With the lateral pronotal lobes of unequal size, the anterior lobe much more prominent than the intermediate lobe, and in having the discomedial costa reduced medially, R. pteronellus is similar to R. hexadentatus and to the group of species including R. blantoni , R. suspiciosus , and R. spilmani that occur in more southern Central America and the West Indies. While species in this group have variable numbers of puncture rows in the intervals between the elytral costae and a reduced discomedian elytral costa, R. pteronellus is readily distinguished by the second costal interval having one row of enormous punctures medially and the discomedian costa completely absent medially.

Presently, worldwide, very few flightless rhyparines are known, the only ones being two species of Nanotermitodius Howden ( Skelley et al. 2022b) also from Mexico. As different surveying methods are employed in more local or isolated habitats worldwide, additional flightless rhyparines will undoubtedly be discovered.