Deltoxenos hajeki Benda & Straka, 2025

Deltoxenos hajeki Benda & Straka sp. nov.

Figs 1 A, B View Figure 1 , 2 A – D View Figure 2 , 3 A – D View Figure 3 , 4 A, B View Figure 4

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 View Figure 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 View Figure 2 ) and a double dark spot (mds, Fig. 2 A View Figure 2 ) 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 View Figure 4 ), 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 View Figure 12 ). From D. maceki it can be distinguished by ventrally exposed clypeal sensilla (cls, Fig. 4 A View Figure 4 ) which are mainly concentrated anteriorly on clypeal lobe in D. maceki . The antennal torulus is slightly reduced but still present (Fig. 4 B View Figure 4 ) while it is completely absent in D. maceki (Fig. 11 C View Figure 11 ).

Description of female cephalothorax.

Shape and colouration. Size of holotype cephalothorax: length 1.74 mm, width 1.42 mm (Fig. 2 C View Figure 2 ). Size of paratype cephalothorax: length 1.62 mm, width 1.52 mm (Fig. 2 A View Figure 2 ). 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 View Figure 2 ). 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 View Figure 3 ), with dark colouration (gr, Fig. 2 A View Figure 2 ). 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 View Figure 4 ). Dorsal side of clypeal area smooth and lacking sensilla (cl, Fig. 4 B View Figure 4 ). Border between clypeal and frontal region indistinct but still present. Frontal region smooth, slightly reticulated (fr, Fig. 4 B View Figure 4 ). Segmental border between head and prothorax indicated by indistinct mesal furrow on dorsal side (sbhp, Fig. 3 B View Figure 3 ) 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 View Figure 3 ) and laterally by suture (sbhp, Fig. 3 A View Figure 3 ).

Supra - antennal sensillary field. Reticulated to completely smooth, with dispersed sensilla inserted in cavities (sssf, Fig. 4 B View Figure 4 ). Distinctly delimited by furrow on medial side (fssf, Fig. 4 B View Figure 4 ). 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 View Figure 4 ). Antennal torulus reduced but still present as furrow between antenna and periantennal area. Periantennal area slightly expanded, smooth (paa, Fig. 4 B View Figure 4 ).

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 View Figure 4 ). In holotype, dorsal field with 11 sensilla inserted in cavities (dlf, Fig. 4 A View Figure 4 ).

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 View Figure 4 ). Cuticle of mandible smooth medially, laterally with longitudinal furrows. Mandibular tooth not curved, pointing dorsally, armed with many spines (mdt, Fig. 4 A View Figure 4 ).

Maxilla. Well-developed and prominent, separated from labial area (mx, Fig. 4 A View Figure 4 ). 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 View Figure 3 ). Vestige of palp present, located medially on ventral side of maxilla (mxp, Fig. 4 A View Figure 4 ). Maxillary base distinctly produced anterolaterally as submaxillary groove. Space between prothoracic extension and head extended (sbhp, mxb, Fig. 3 A View Figure 3 ).

Labium. Labial area between maxillae distinct, delimited anteriorly by mouth opening and posteriorly by birth opening (lb, Fig. 4 A View Figure 4 ). 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 View Figure 4 ).

Thorax. Pro-mesothoracic and meso-metathoracic borders visible ventrally as slightly imprinted mesal furrows (sbpm, sbmm, Figs 2 A View Figure 2 , 3 A View Figure 3 ). On dorsal side separated by conspicuous dark mesal furrows, distinctly contrasting with pale thoracic segments (sbpm, sbmm, Figs 2 B View Figure 2 , 3 B View Figure 3 ). 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 View Figure 3 ), posteriorly with conspicuous dark spot (pds, Fig. 2 A View Figure 2 ). Mesosternum almost completely covered with dark papillae except mesal double dark spot (mds, Fig. 2 A View Figure 2 ). 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 View Figure 3 ). 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 View Figure 2 ).

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.