Deltoxenos hajeki Benda & Straka 2025, sp. nov.

Deltoxenos hajeki Benda & Straka sp. nov. Figs 1 A, B, 2 A – D, 3 A – D, 4 A, B Type material. Holotype • ♀ (NMPC), Solomon Islands: Guadalcanal, 4.5 km S of Barana, 275 m, 6.xii.2013, host: Phimenes solomonis (Vecht, 1959), J. Hájek lgt. Paratype • ♀ (NMPC), data the same as holotype, from the same host specimen as holotype (Fig. 1). Diagnosis of female cephalothorax. This species is easily distinguished from other representatives of the genus Deltoxenos by a conspicuous dark spot posteriorly on the prosternum (pds, Fig. 2 A) and a double dark spot (mds, Fig. 2 A) situated mesally on the mesosternum. The cuticular surface of the prosternal and mesosternal dark spots is smooth, without any papillae or reticulation. It differs from D. indonesiensis and D. reginus by well-developed and prominent maxillae, separated from the labial area (mx, Fig. 4 A), and by the mostly pale colouration of the prosternum and mesosternum. It differs from D. rueppelli by a rounded and protruding clypeal lobe (cl, Fig. 12). From D. maceki it can be distinguished by ventrally exposed clypeal sensilla (cls, Fig. 4 A) which are mainly concentrated anteriorly on clypeal lobe in D. maceki. The antennal torulus is slightly reduced but still present (Fig. 4 B) while it is completely absent in D. maceki (Fig. 11 C). Description of female cephalothorax. Shape and colouration. Size of holotype cephalothorax: length 1.74 mm, width 1.42 mm (Fig. 2 C). Size of paratype cephalothorax: length 1.62 mm, width 1.52 mm (Fig. 2 A). Cephalothorax variable in size, but always distinctly longer than wide; paratype shorter and wider than holotype. Constriction at pro-mesothoracic segmental border not visible; meso-metathoracic segmental border conspicuously constricted laterally (sbmm, Fig. 2 C). Abdominal segment I not protruding laterally, corner below spiracles rounded. Anterior head margin rounded, slightly protruding from remaining head capsule. Thorax elongated, very slightly widening posteriorly. Cephalothorax with conspicuously contrasting pale and dark colour pattern but predominantly pale. Head capsule. Length proportion of head / cephalothorax 0.44–0.45 including lateral cephalic extension. Colouration forming specific pattern with predominantly pale parts and dark brown mandible and labium. Surface of lateral extensions at site of reduced compound eyes smooth, laterally with conspicuous longitudinal grooves visible on SEM images (gr, Fig. 3 A), with dark colouration (gr, Fig. 2 A). Clypeal area well delimited from labral area, arcuate, clypeal lobe slightly protruding from head capsule. Surface completely smooth with slightly> 44 distinctly exposed sensilla mainly concentrated on clypeal lobe on ventral side (cls, Fig. 4 A). Dorsal side of clypeal area smooth and lacking sensilla (cl, Fig. 4 B). Border between clypeal and frontal region indistinct but still present. Frontal region smooth, slightly reticulated (fr, Fig. 4 B). Segmental border between head and prothorax indicated by indistinct mesal furrow on dorsal side (sbhp, Fig. 3 B) and by dorsal transverse stripe of reticulated cuticular surface on frontal region. Head and prothorax distinctly separated by birth opening ventromedially (bo, Fig. 3 A) and laterally by suture (sbhp, Fig. 3 A). Supra - antennal sensillary field. Reticulated to completely smooth, with dispersed sensilla inserted in cavities (sssf, Fig. 4 B). Distinctly delimited by furrow on medial side (fssf, Fig. 4 B). Surface of supra-antennal sensillary field and frontal region with different sculpture. Antenna. Preserved as well-defined area, with numerous vestigial sensilla, distinct rounded plates and inconspicuous cavities (a, Fig. 4 B). Antennal torulus reduced but still present as furrow between antenna and periantennal area. Periantennal area slightly expanded, smooth (paa, Fig. 4 B). Labrum. Ventral field wider than long, elliptic. Dorsal field very slightly arcuate, flat, not raised, laterally not narrower than medially, 4 × wider than long in midline (vlf, dlf, Fig. 4 A). In holotype, dorsal field with 11 sensilla inserted in cavities (dlf, Fig. 4 A). Mandible. Mandibles anteromedially directed at angle of 40–45 ° (45 ° in holotype), enclosed within mandibular capsule. Mandibular bulge distinctly raised, elongated, anteriorly directed, with several sensilla (mdb, Fig. 4 A). Cuticle of mandible smooth medially, laterally with longitudinal furrows. Mandibular tooth not curved, pointing dorsally, armed with many spines (mdt, Fig. 4 A). Maxilla. Well-developed and prominent, separated from labial area (mx, Fig. 4 A). Mostly with pale colouration, cuticle smooth or slightly reticulated. Apical maxillary region not projecting beyond mandibular apex. Basal part connected with labium and not overlapping with mandible (mxb, Fig. 3 A). Vestige of palp present, located medially on ventral side of maxilla (mxp, Fig. 4 A). Maxillary base distinctly produced anterolaterally as submaxillary groove. Space between prothoracic extension and head extended (sbhp, mxb, Fig. 3 A). Labium. Labial area between maxillae distinct, delimited anteriorly by mouth opening and posteriorly by birth opening (lb, Fig. 4 A). Flat, approximately as long as wide. Cuticular surface smooth to very slightly reticulated. Mouth opening. Widely arcuate but not semicircular, sclerotised along margin (os, Fig. 4 A). Thorax. Pro-mesothoracic and meso-metathoracic borders visible ventrally as slightly imprinted mesal furrows (sbpm, sbmm, Figs 2 A, 3 A). On dorsal side separated by conspicuous dark mesal furrows, distinctly contrasting with pale thoracic segments (sbpm, sbmm, Figs 2 B, 3 B). Border between metathorax and abdomen indicated by ventral ridge on ventral side or indicated by change in colour and cuticular sculpture. Cuticle of thoracic segments on ventral side mostly reticulated, uniformly scattered with inconspicuous or more distinct pigmented papillae, except dark spots. Prosternum differentiated, anteriorly with field of dozens of sensilla (psf, Fig. 3 A, C), posteriorly with conspicuous dark spot (pds, Fig. 2 A). Mesosternum almost completely covered with dark papillae except mesal double dark spot (mds, Fig. 2 A). Cuticular surface of prosternal and mesosternal dark spots smooth, without any papillae or reticulation. All thoracic segments dorsally pale, but darker laterally. Meso- and metathorax transverse, rarely slightly elongated. Abdominal segment I and spiracles. Setae and cuticular spines present on lateral region of abdominal segment I posterior to spiracle (Fig. 3 D). Spiracles on posterior ~ 2 / 5 of cephalothorax, very slightly elevated, with lateral or dorsolateral orientation. Cephalothoracic part of abdominal segment I below spiracles dark brown on both sides (asI, Fig. 2 D). Host. Phimenes solomonis (Vecht, 1959) Phylogenetic relationships. Unknown. Distribution. Solomon Islands. Etymology. Named after Jiří Hájek (National Museum of the Czech Republic, Prague), a dear colleague and expert on aquatic beetles, who collected the type material.