Bibrax yasuni sp. nov. Figs 5 I, J, 8 A – E Type material. Holotype • ♂ (QCAZ -I-278674): “ Ecuador. Orellana, Estación Científica Yasuní PUCE, 253 m, -0.68315, -76.40004, 09 - 2017. Winkler., A. Argoti & R. E. Cárdenas ” / “ Caterino DNA voucher, Ext. MSC-13225, Morphosp. 278674 ” / “ QCAZ -278674 ”. Paratype • 1 ♂: “ Ecuador: Yasuni National Park, Yasuni Biological Station, 0°40'32"S, 76°23'50"W ” / “ 29 June 1999, Berlese, 15 km West of station, Monkey Plot, CEC # 034, CECarlton ” (QCAZ -I-280395). Diagnosis. BL = 1.76 mm (n = 1). Body setose and reddish, finely punctate above; head rounded posteriorly, vertexal foveae slightly impressed; frons narrowing and rising to common antennal base; eyes reduced, with two or three ommatidia; gular teeth well-developed; scape elongate, weakly sinuate, antennomere II (pedicel) slightly longer than III – VI combined, narrow at base and widening towards distal end, with outer margin straight, inner apical angle protruding forming flattened, slightly translucent, rounded spatulate process, III-VIII bead-like, V and VII slightly longer and bearing elongate setae, antennomeres IX – XI forming loose club, IX and X slightly transverse and bearing elongate setae, XI densely setose; pronotum elongate, widest near front, sides rounded; pronotal disk with lateral and median subbasal foveae; disk with strongly marked lateral longitudinal impressions; elytra rather short (wingless), sides rounded, each elytron with sutural and lateral basal foveae, lateral fovea with strong impression running posterad; subhumeral fovea absent; outer posterior corner of each elytron with tooth; dorsal surface of abdomen largely impunctate; protibia swollen; metatrochanter with distal corner extended as strong spine; metafemora swollen, distinctly clavate; last abdominal ventrite bearing small median apical marginal flange; penultimate ventrite shorter, barely depressed at middle. Aedeagus (Fig. 5 I, J) with round basal diaphragm, short and irregularly subspherical basal bulb; basal apodemes conjoined, broad, flat, with prolonged apical corners; tegmen narrow and tubular at base, expanded distally, dorsally hooded, with strong, blunt ventral keel, two distal processes that are similar in length extend from ventral apex, one thinner, slightly sinuate and apically subacute, the other wider, with basal brush of setae along outer margin, apically bifid with sclerotized, acute tip and secondary, setose, unsclerotized apical lobe; expansive membranous internal sac surrounding much of tegmen apex. Distribution. This species is known only from the Yasuní Biological Station in Amazonian Ecuador. Remarks. As discussed above, this species is very similar to the preceding. Aside from the distinctive male genitalia, B. yasuni is most distinct in the shape of antennomere II of the male, having a straight outer margin and flanged inner apical corner, the male penultimate abdominal ventrite, being shorter and barely depressed at the middle, and in the apically prolonged male metatrochanter. Etymology. This species is named for the Yasuní Biological Station, its type locality.

Published as part of Tapuy-Avilés, Yarina, Díaz-Guevara, David R. & Caterino, Michael S., 2025, First record of Bibrax Fletcher, 1927 (Coleoptera, Staphylinidae, Pselaphinae) from Ecuador, with descriptions of twelve new species, pp. 105-133 in ZooKeys 1250 on pages 105-133, DOI: 10.3897/zookeys.1250.156763