Psepehenops arcei Luna-Luna, Chacón-Hartleven & Contreras-Ramos, 2025

Psepehenops arcei Luna-Luna, Chacón-Hartleven & Contreras-Ramos , sp. nov.

Figs. 9–15 View FIGURES 9–15

Diagnosis. Adult male ( Figs. 9–15 View FIGURES 9–15 ): body oval and depressed; head short, transverse, antennae short, not reaching pronotal base, moniliform; pronotum subtrapezoidal, anterior margin arcuate, posterior margin bisinuate, straight in antescutellar area. Pronotal disc with well-developed, medial, longitudinal carina on distal half. Protibia with a tiny apicolateral denticle and long tarsal lobes. Male genitalia ( Figs.13–15 View FIGURES 9–15 ): short, wide, subrectangular, trilobate; parameres robust and elongate, close to each other with internal margins fused in dorsal view, apex rounded. Penis digitiform, acuminate apically in dorsal view; apically narrowed, directed ventrally. Psephenops arcei , sp. nov. is close to P. triangularis of Panama by sharing smooth elytra and elongated tarsal lobes (lobe of tarsomere 2 covers ventrally the full-length of tarsomeres 3-4 and reaching at least 80% the length of tarsomere 5). Characters of the genitalia may separate males of both species: in the new species ( Figs. 13, 14 View FIGURES 9–15 ), parameres in dorsal view are medially close to each other, with margins smooth in ventrolateral view, while in P. triangularis the parameres are medially broadly separate, with an evident tooth on inner margin near the apex. The penis in the new species is digitiform, apically acuminate ( Figs. 13, 14 View FIGURES 9–15 ), while in P. triangularis it is digitiform, with a basal, lateral, subtriangular projection from each side.

Description. Male: body length X̅ (mean) = 2.7 mm, width X̅ = 1.5 mm (n = 3). Body oval, depressed; integument yellowish-brown, head black; pronotum dark; elytra yellowish-brown, covered with short yellow setae with golden reflections ( Figs. 9, 11 View FIGURES 9–15 ); coxae, trochanters, and femora reddish-brown; tibiae and tarsi reddish brown with vestiture short, fine and dense, yellowish-gray ( Fig. 10 View FIGURES 9–15 ).

Head: cypeus subrectangular, declivous at less than 90 degrees from plane of frons, distal margin widely emarginate; fronto-clypeal surface and vertex with long yellowish-brown setae, vertex minutely punctate. Antennae short ( i.e., when fully extended backwards, not reaching posterior margin of pronotum), moniliform, with 11 antennomeres; scape longest, pedicel subglobose, half as long as scape; third antennomere subtriangular, pale brown, shorter than pedicel; antennomeres 4–10 small, moniliform; apical antennomere acuminate and dark brown ( Fig. 9 View FIGURES 9–15 ). Eyes lateral, rounded, very prominent, reddish-brown, with dark brown postocular area ( Fig. 11 View FIGURES 9–15 ). Labrum subrectangular, similar to clypeus but shorter. Maxillary palp with 4 palpomeres, covered with long setae, basal palpomere smallest, apical palpomere longest, with wide sensory area, relative length of palpomeres 0.04, 0.08, 0.06, 0.14; palpomeres 1–3 subconical, palpomere 4 acuminate. Labial palp short, with 3 palpomeres, palpomeres 1–2 rounded and wide, palpomere 3 subconical, nipple-shaped and slightly longer than preceding ones.

Thorax: pronotum width X̅ = 1.14 mm (n = 3); lateral margin length X̅ = 0.60 mm (n = 3). Black, subtrapezoidal, basally almost as wide as elytral base; anterior margin arcuate, posterior margin bisinuate, straight in antescutellar area, expanded posterolaterally; posterolateral angles subacute. Pronotal disc with well-developed, dorsomedial, longitudinal carina on distal half, and wide, oval, deep depression at each side of carina ( Fig. 9 View FIGURES 9–15 ); pronotal surface finely punctate, with minute, yellowish-brown vestiture, and long, dark brown setae. Scutellum short, apex rounded. Elytra with short yellow setae producing golden shining and long yellowish-brown setae; lateral margins parallel on basal three-fourths, then gradually converging posteriorly; humeral width 1.10 mm; surface without striae; length (from base to apex of suture) 1.45 mm; elytral base dark brown. Prosternum dark brown, short; prosternal process lanceolate, deeply grooved longitudinally, apex concave( Fig. 10 View FIGURES 9–15 ) reaching anterior half of mesoventrite; mesoventrite shorter than metaventrite, with wide groove receiving prosternal process; metaventrite large and bulky. Legs ( Figs. 10, 12 View FIGURES 9–15 ): femora robust; tibiae slender, metatibia longer than metafemur, protibia with tiny apicolateral denticle; tarsomeres 1 and 2 ventrally lobed, with thick sponge-like vestiture; ventral lobe of tarsomere 1 extending over basal 0.30 of tarsomere 2; tarsomere 2 the longest, twice as long as tarsomere 1, extending distally and completely covering tarsomeres 3, 4, and basal 0.80 of tarsomere 5; apical claws long, curved, slender, each with small basal tooth.

Abdomen: vestiture short, fine, dense, and grayish. Ventrite VI usually hidden under ventrite V; ventrites I and II wide, with posterior margin curved anteriorly in the middle; ventrites III and IV narrow, with posterior margin straight; ventrite V with posterior margin slightly emarginate; ventrite VI short, subtriangular, with posterior margin widely curved posteriorly; ventrite VII or anal plate, oval, subtriangular, narrow, covered with long whitish setae; pygidium oval, partly concealed, emarginate, with long brown setae.

Male genitalia: short, wide, subrectangular, trilobate ( Figs. 13–15 View FIGURES 9–15 ); total length 0.60 mm, total width 0.24 mm. Parameres robust and elongate, 0.40 mm long, shorter than penis, uniformly widened, apex rounded; with internal margins fused at basal 0.2 in dorsal view ( Fig. 13 View FIGURES 9–15 ). Penis length X̅ = 0.49 mm (n = 3), longer than parameres ( Figs. 13–15 View FIGURES 9–15 ); phallobase concave in dorsal view, bulky-subcylindrical in ventral view, length X̅ = 0.25 mm, width X̅ = 0.23 mm (n = 3) ( Fig. 13 View FIGURES 9–15 ); apical half, subtriangular, lanceolate in ventral view ( Fig. 14 View FIGURES 9–15 ); apically narrowed, directed ventrally ( Fig. 15 View FIGURES 9–15 ).

Variation. One specimen does not present a dark brown coloration at distal portion of the elytra, body length range was 2.6–2.8 mm (n = 3).

Holotype. MEXICO: Chiapas: Ocosingo, Reserva de la Biosfera Montes Azules, Estación de Biología Chajul, Río Lacantún (embarcadero), 16°06’38.4”N, 90°56’23.6”W, 154 m, 12.i.2017, Barba, 1 male, D net ( CNIN). GoogleMaps

Paratypes. MEXICO: Chiapas: Marqués de Comillas, río Ixcán (embarcadero), Rta.307 Palenque-La Trinitaria , 16°05’22.43”N, 91°05’19.42”W, 150 m, 22.ii.2016, Barba , Mayorga , 1 male ( CNIN); Marqués de Comillas , río Ixcán (embarcadero), Rta. 307 Palenque-La Trinitaria, 16°05’34.45”N, 91°05’30.11”W, 166 m, 8.i.2017, Barba, 1 male ( CNIN) GoogleMaps .

Geographical distribution. MEXICO, Chiapas, Ocosingo and Marqués de Comillas municipalities.

Etymology. This species is named after entomologist Roberto Arce-Pérez, for his contribution to the taxonomy of aquatic Coleoptera of Mexico, including Psephenidae .

Habitat. Specimens were collected in the riparian zones of large, unwadable rivers. The holotype was collected in the Lacantún River, a tributary of Usumacinta river, draining remnants of tropical rainforest, and characterized by a highly turbulent water flow, with channel elements dominated by fast-flowing habitats ( e.g., rapids and riffles), and inorganic substrate dominated by cobbles. Specimens from Marqués de Comillas ( paratypes) were collected at Ixcán River, from the sub-basin Lacantún River. The river had scarce riparian vegetation and a highly turbulent water flow, with channel elements dominated by fast-flowing habitats ( e.g., rapids and riffles) and inorganic substrate dominated by pebbles.