Bostrichoclerus bicornus Van Dyke, 1938

Burke, Alan F., Leavengood, John M., Scholtz, Clarke H. & Sole, Catherine L., 2019, Redescription of the holotype of Bostrichoclerus bicornus Van Dyke, 1938, a rare species of the New World Tillinae Fauna (Coleoptera: Cleridae), with some taxonomic notes, Zootaxa 4544 (4), pp. 548-556 : 549-553

Bostrichoclerus bicornus Van Dyke, 1938

( Figs 1–8 , 10–13 , 19 )

Type species. Bostrichoclerus bicornus Van Dyke, 1938 , original designation (monotypy).

Type locality. Palm Cañon, Angel de la Guardia, Golf of California , Mexico . Type depository: California Academy of Sciences ( CASC) .

Material examined: Holotype, a female, red labelled ( Fig. 19 ): Angel de la Guardia Isd, Palm Cn., Gulf Calif., May-3-1921, J.C. Chamberlin Collector, apparently near genus Natalis , California Academy of Sciences Entomology Type no. 4682. Abdomen attached to a cardboard piece ( Figs 8 , 19 ).

Differential diagnosis: The structure of the antennae ( Fig. 4 ) as well as the bisinuate lateral margin of the pronotum ( Fig. 1 ) of B. bicornus resemble members of the speciose genus Cymatodera . The former species is easily recognized from Cymatodera and other Tillinae species based on the prominent frontal horns ( Figs 2, 3, 5 ) and the elytral disc lacking clear rows of striae ( Fig. 1 ). This combination of characters is not found in any other Tillinae species. In addition to the frontal horns and the absence of clear rows of striae, B. bicornus has simple tarsal claws ( Figs 12-13 ). With the exception of Onychotillus Chapin , where simple tarsal claws are also seen, remaining genera of New World Tillinae have the tarsal claws with two denticles.

Description: Holotype female. TL = 22.57 mm. Form elongate, slightly robust; metathoracic wings fully developed. Color: Head, pronotum, elytra, antennae and legs piceous; mouthparts, prosternum, mesoventrite and metaventrite dark ferrugineous; serrate portion of antennomeres 6–11 more testaceous due to patches of sensillae; elytral surface without any markings or bands ( Figs 1, 4 , 10 ).

Head: HL = 3.84 mm, HW = 3.95 mm (note: due to the head pointing forward, visibility of the anterior portion of the head is reduced). Prognathous. Measured across eyes narrower than pronotum; surface smooth, shiny, finely, scarcely punctate; frons not impressed, rather excavated; clothed with short, very fine, scarce semirecumbent setae and few scattered long, erect setae. Eyes of moderate size, rounded, slightly ovoid in lateral view; conspicuously bulging laterally; very feebly emarginated in front; ommatidia moderately wide ( Figs 2–3, 5 , 12 ). A pair of prominent horns laterally compressed ( Figs 3, 4, 5 ), bifid posteriorly ( Fig. 2 ). Horns arising from just above the eye emargination at their upper end ( Figs 2, 3 ) and below the antennal insertion at their lower end ( Fig. 3 ), giving the impression that the antennae arise from the base of horns. Antennae moderately slender; antennomeres 2–5 approximately the same length, antennomeres 6–11 subequal in length, about 2/3 the length of fifth antennomere; antennomeres 2–4 cylindrical; fifth antennomere feebly serrate, antennomeres 6–10 serrate; eleventh antennomere ovoid, acuminated apically ( Figs 1, 4 ). Labial palpi composed of 3 palpomeres, maxillary palpi composed of 4 palpomeres; terminal labial palpomeres securiform, terminal maxillary palpomeres subsecuriform ( Fig. 10 ).

Thorax: PL = 5.60 mm, PW = 4.36 mm. Pronotum elongate, longer than broad; widest behind middle; narrow at sides in front and behind middle, more strongly constricted at posterior margin ( Fig. 1 ). Dorsolateral ridge absent ( Fig. 11 ). Disc flat; surface shiny, feebly rugose, finely punctate; vested with short, pale, recumbent setae interspersed with few, long, erect setae; posterior margin with pronotal collar complete. Procoxae rounded; procoxal cavities partially opened internally, completely closed posteriorly by the pronotal projection, rendering the procoxal cavities partially opened behind ( Fig. 6 , see arrows); prosternal process wider posteriorly ( Fig. 6 ). Prosternum conspicuously wider than long; surface shiny, smooth, shallowly punctate, feebly vested with some scattered recumbent setae. Mesoventrite shiny; feebly concave, coarsely punctate; vested with scattered, long, semi-erect setae. Metaventrite much longer than wide, strongly convex, rugulose, shallowly punctate, clothed with fine, pale, semirecumbent setae; mesepisternum visible throughout its length ( Fig. 7 ). Anterior portion of metacoxal cavities lacking a pair of perpendicular carinae ( Figs 8, 9 ). Scutellum semicircular in shape, as wide as long; moderately setose.

Legs: Femora moderately slender, not dilated distally; tibiae slender, elongate. Tibial spur formula 2-2-2; tarsal formula 5-5-5, first 4 tarsomeres greatly expanded, forming pulvilli ( Figs 12–13 ), densely setose from below ( Fig. 12 ), 4 pulvilli visible from dorsal view. Tarsal pulvilli feebly emarginate ( Fig. 12 ). Tarsal claws without inner denticle ( Figs 12, 13 ).

Elytra: EL = 15.06 mm, EW = 6.33 mm. Elytral base wider than widest portion of pronotum; sides subparallel, widest just behind middle; disc feebly convex; apex acuminate, very feebly dehiscent. Humeri rounded. Elytral disc surface coarsely rugose. Elytral sculpturing consisting of numerous fine punctations densely, irregularly arranged; punctations do not form regular, well defined striae, but rather a rugulose disc ( Fig. 1 ). Epipleural fold complete. Clothed with short, pale, recumbent setae intermixed with scattered, long, erect setae.

Abdomen: Composed of six visible segments. Ventrites 1–4 subquadrate, rugulose, conspicuously, finely punctate. Fifth visible ventrite moderately convex; subtriangular; surface shiny, moderately, shallowly, finely punctate; lateral margins oblique; posterolateral angles rounded; posterior margin truncate with a median, narrow, shallow emargination. Sixth visible ventrite small; broader than long; surface feebly convex, shiny; moderately, finely and shallowly punctate; lateral margins strongly convex, hind margin reduced, shallowly, broadly emarginate. Sixth tergite extending beyond apical margin of sixth visible ventrite; base of sixth visible ventrite extending laterally, slightly farther than sixth tergite ( Fig. 8 ).

Type locality: The type material was collected at a single locality in Palm Canyon, Angel de la Guarda Island. This is a semiarid island part of the Mexican state of Baja California. According to the original description of Van Dyke (1938), the specimen was captured beneath the bark of an unknown plant species.

Figures

FIGURES 1–5. 1. Habitus of the holotype of B. bicornus, 2. Close-up of the frons in dorsal view of the holotype of B. bicornus, 3. Head in dorsolateral view the holotype of B. bicornus, 4. Head and antennae in dorsal view of the holotype of B. bicornus, 5. Head in dorsal view of the holotype of B. bicornus.

FIGURES 6–9. 6. Prosternum and procoxal cavities of the holotype of B. bicornus, arrows indicate posterior portion of procoxal cavities partially open internally, 7. Mesoventrite of the holotype of B. bicornus, arrows indicate mesepisterna visible in ventral view, 8. Abdomen of the holotype of B. bicornus with metacoxae removed, 9. Abdomen of Cymatodera balteata LeConte with metacoxae removed, arrows indicate perpendicular carinae.

FIGURES 10–13. 10. Mouthparts of the holotype of B. bicornus, 11. Pronotum in lateral view of the holotype of B. bicornus, 12. Protarsomeres in ventral view of the holotype of B. bicornus, 13. Protarsomeres in lateral view of the holotype of B. bicornus.

FIGURES 17–19. Prosterna with procoxae removed of 17. Enoclerus zonatus (Klug), 18. Cymatodera sallei Gorham, 19. Labels of the holotype of B. bicornus, notice the abdomen attached to a cardboard piece.