Basothorhynchus, Borovec, 2019

Borovec, Roman, 2019, Basothorhynchus, a new Oosomini genus from the highland plateau of Lesotho (Coleoptera: Curculionidae: Entiminae), Zootaxa 4550 (3), pp. 416-422 : 417-419

Basothorhynchus gen. nov.

Type species. Basothorhynchus endroedyi sp. nov., by present designation.

Diagnosis. Small-sized genus with dorsal surface of body glabrous; rostrum evenly tapered apicad with straight sides, posteriorly continuous with head; base of epifrons as wide as space between anterior margins of eyes, apex narrower than half width of rostrum; frons glabrous, smooth; epistome slightly carinate; scrobes placed dorsally; scape short, not reaching anterior border of pronotum in repose; elytron without humeral callus; all femora with distinct tooth; tibiae slender at basal third and here abruptly enlarged inside, apical two thirds of tibiae subparallelsided, outer edge straight; metatibiae lacking corbel; claws free; tegmen bearing two parameres; female sternite VIII with plate about as long as apodeme; plate narrowly subtriangular, apically pointed, with two longitudinal sclerites at distal three quarters, apical margin sclerotised, and basal margin ill-defined.

Description. Body length 2.3–3.0 mm.

Body integument dark brownish to blackish ( Fig. 1 ). Antennae and legs paler, rusty brownish, covered with short, fine, semi-erect setae; only clubs slightly darker, finely and densely setose. Dorsal side of body glabrous, lacking appressed scales or setae, with inconspicuous fine, slender erect setae on elytra and shorter semi-erect setae on pronotum and head plus rostrum. Head and rostrum glabrous on ventral side; sternum densely covered by oval greyish appressed scales; abdominal ventrites covered with short, fine, sparse, semi-appressed setae and several individual appressed scales in lateral parts of ventrites 1 and 2..

Head wide and short, slightly enlarged posteriad, vertex flat, shorter than half length of eye; ventrally unpunctured, smooth. Eyes moderately large, subdorsal, hardly prominent from outline of head; laterally subcircular, not reaching dorsal border of head. Rostrum ( Figs 2, 3 ) short, 1.1–1.2 × as wide as long, evenly tapered apicad, at base 1.1 × as wide as at apex; dorsal border convex and ventral border straight in profile. Epifrons widest at base, conspicuously tapered apicad, with faintly concave sides, distinctly carinate laterally, at base as wide as space between anterior margins of eyes, at apical half slightly narrower than half width of rostrum in the same place, extending apically to level of anterior border of scrobes, median carina present along apical half; rostrum posteriorly continuous with head. Frons glabrous, smooth, yellowish-brown, moderately shiny, not separated posteriorly from epifrons, with five to six prominent pairs of stout setae apically. Epistome emarginate at apex, carinate, separated from frons by a keel. Scrobes placed dorsally, in dorsal view fully visible in apical third of rostrum as deep, oval fossae, broadly reniform; furrow-shaped, with conspicuous dorsal and ventral edges, and directed towards eye in lateral view, ventral margin terminated slighty above ventral margin of eye. Venter of rostrum shallowly depressed on the whole surface, covered with semi-appressed sparse setae. Mandibles small, projecting anteriorly, lacking scales, with three laterally placed setae.

Antennae ( Fig. 1 ) moderately short and robust. Scape not reaching anterior border of pronotum in repose, 1.1 × longer than funicle; funicle 7-segmented, segment 1 long and conical (the longest), segments 3–7 isodiametric to wider than long; club broadly oval.

Pronotum ( Fig. 1 ) 1.1 × wider than long, with distinctly rounded sides; disc regularly convex without any keel, furrow or depression; base slightly arched. Anterior border of pronotum laterally straight without ocular lobes or setae. Procoxal cavities contiguous, round, placed at midlength of pronotum.

Scutellum triangular, very small, hardly visible.

Elytra ( Fig. 1 ) oval, 1.3–1.5 × longer than wide; humeri weakly rounded, lacking a distinct callus; base slightly wider than base of pronotum, distinctly arched, widest at midlength; apex broadly rounded; sides slightly convex, slope of declivity hardly overhanging apices of elytra in dorsal view. Elytra 10-striate; striae punctate, intervals flat. Mesocoxae semiglobular, mesosternal process narrow, about as wide as 1/5 of mesocoxal width. Metacoxae semiglobular, metaventral process obtuse, narrower than transverse diameter of metacoxa. Tergite VII ( Fig. 4 ) of males short and wide, apically V-shaped concave with straight sides; tergite VIII ( Fig. 4 ) of males well sclerotised, bowl-shaped, apically weakly rounded. Tergite VII and VIII of females larger than those in males, weakly sclerotised, apically rounded.

Legs moderately robust. Femora ( Fig. 5 ) swollen, all femora with distinct tooth equal in both sexes, almost as large as half the width of femora at this level, concave at inner edge. Procoxae subglobular, protibiae ( Fig. 5 ) short and robust, laterally straight, slender at basal third and abruptly enlarged distad, inside with inner edge slightly concave and with three to six small brownish teeth, apex rounded and densely fringed by brown bristles, mucronate. Meso- and metatibiae weakly enlarged outside. Metatibial apex oval, glabrous fringed externally and internally with dense brown bristles. Tarsi with segment 3 bilobed, distinctly wider than segment 1 and 2; onychium long; claws free, weakly divaricate.

Abdomen ( Fig. 6 ) 1.2–1.3 × longer than wide, with rounded sides; ventrite 1 twice as long as ventrite 2, behind metacoxa equally long as ventrite 2; ventrite 2 slightly shorter than ventrites 3 and 4 combined; ventrite 5 of males subtrapezoidal, short, shallowly concave at apex, ventrite 5 of females subtriangular, longer than in males, convex, apically rounded. Suture between ventrites 1 and 2 indistinctly sinuose, fine and narrow; all other sutures straight, deep and moderately wide.

Sexual dimorphism. Males distinguishable from females by the more slender elytra, the wider and shorter tarsi, and the shape and concavity of ventrite 5.

Male terminalia. Penis ( Fig. 7 ) short, well sclerotised, temones 1.4–1.5 × longer than body of penis; endophallus long, with two moderately long, basally connected sclerites and one short transverse arched sclerite placed distally. Tegmen ( Fig. 8 ) slender, parameres distinct, fused at base and distinctly shorter than diameter of ring, manubrium 1.4 × as long as diameter of ring, 0.8 × as long as temones. Spiculum gastrale moderately short, anteriorly curved and enlarged to form a narrow plate, posteriorly with fused basal arms; hemisternites very slender, curved.

Female terminalia. Sternite VIII ( Fig. 9 ) with plate subtriangular, widest near base, 2.4–2.6 × as long as wide, apically sharply pointed and bearing two separate tufts of setae, with two longitudinal sclerites at apical three quarters; apodeme longer than sternite VIII, widest at midlength, terminating just at midlength of plate, at base enlarged to small, triangular translucent plate. Gonocoxites ( Fig. 10 ) flat, long, tapered apically, with long apical styli bearing apical setae. Spermatheca ( Fig. 11 ) U-shaped with regularly curved wide cornu, elongated corpus, short ramus (= gland entrance) and indistinct collum (= duct entrance).

Etymology. The new genus is derived from the word Basotho and Latin rhynchus. Basotho is a Bantu ethnic group whose ancestors have lived in southern Africa since around the fifth century. Most Basotho people today live in South Africa and Lesotho ( Gardner et al. 1999). Rhynchus is the Latin form of the Greek word rhynkhos, having a snout, bill, beak. The name is of male gender.

Distribution. Known only from Lesotho.

Species included. The genus is described as monotypic, including only the species B. endroedyi .

Taxonomic position. The newly described genus belongs to the subfamily Entiminae, as defined by Marvaldi et al. (2014), and here to the Oosomini, based on its free claws (this character distinguishes it from the Embrithini Marshall, 1942 ), trisetose mandibles (distinguishing it from the Otiorhynchini Schoenherr, 1826 ), dorsally placed scrobes (distinguishing it from the Brachyderini Schoenherr, 1826 and Sciaphilini Sharp, 1891 ), lack of ocular lobes and vibrissae (distinguishing it from the Tanyrhynchini Schoenherr, 1826 and Tanymecini Lacordaire, 1863 ), and lack of a protruding humeral callus (distinguishing it from the Polydrusini Schoenherr, 1823 ).

Oosomini were never redefined after Marshall (1942) split them into Oosomini with free claws and Embrithini with fused claws. This tribe does not seem to be monophyletic and a further study is much needed. Oosomini contains fewer genera than is listed in Alonso-Zarazaga & Lyal (1999) because some genera were later transferred to other tribes (for example Borovec & Oberprieler (2013)).

Endemic to South Africa, Basothorhynchus gen. n. can be easily distinguished from genera of Oosomini comprising large-sized species by the following characters: small size (maximum length 3.0 mm), rostrum posteriorly continuous with head, base of epifrons as wide as space width between anterior margins of eyes, epistome slightly emarginate, scape not reaching anterior border of pronotum in repose, dentate femora, tibiae short and robust, abruptly enlarged to inner side at basal third and body glabrous lacking appressed vestiture. Other genera of Oosomini have larger species (over 5.8 mm long), covered by appressed scales, rostrum posteriorly separated from head by a transverse sulcus or shallow groove, base of epifrons distinctly narrower than width between anterior margins of eyes, epistome conspicuous (except in Phlyctinus ), scape in repose exceeding anterior border of pronotum, adentate femora, tibiae long, slender, slightly sinuose on inner edge.

By its small size, Basothorhynchus can be compared only with three Oosomini genera: Holcolaccus Marshall, 1953 , Oosomus Schoenherr, 1826 and Periderces Marshall, 1926 . From all these three genera Basothorhynchus gen. n. may be distinguished according to the following key:

1. Rostrum at least 1.5 × as long as wide, widest at apical portion with sides rounded around scrobes. Metatibial apex with wide, sparsely squamose corbels. Sternite VIII of females with plate wider than long, apodeme 3.3–6.2 × longer than plate. Size 2.3– 5.1 mm ................................................................................................................................................................................... Oosomus Schoenherr

- Rostrum wider than long or at most 1.2 × as long as wide, widest at base and tapered anteriad, not rounded around scrobes. Metatibial apex simple (= without corbels). Sternite VIII of females with plate distinctly longer than wide, apodeme short, about same length as plate............................................................................... 2

2. Body dorsally and ventrally glabrous. Scrobes dorsally conspicuous, pit-shaped, laterally directed towards eyes. Antennal scape short and robust, 4.9–5.3 × as long as wide at apex. Tibiae slender at basal third and then abruptly enlarged. Size 2.3–3.0 mm.............................................................................. Basothorhynchus gen. n.

- Body dorsally and ventrally squamose. Scrobes not visible from above, laterally not continuing behind antennal insertion or curved downwords. Antennal scape long and slender, 9.1–10.7 × as long as wide at apex. Tibiae slender and long, slightly sinuate at inner side...................................................................................... 3

3. Scrobes very narrow and not continuing backwards. Antennal scape shortly exceeding anterior border of pronotum. Epifrons narrow (about as wide as half rostral width). Femora adentate. Size 2.5–3.8 mm ................... Holcolaccus Marshall

- Scrobes continuing backwards and curved downwards. Antennal scapes not reaching posterior margin of eyes. Epifrons wide (occuping most rostral surface). Femora with large tooth. Size 4.0– 4.8 mm ......................... Periderces Marshall

By its general appearance, small size and glabrous, cylindrical body, Basothorhynchus gen. n. resembles a group of genera known from high elevation mountains of Kenya, such as Abarypeithes Hustache, 1939 , Afrotroglorrhynchus Hustache, 1939 , Hobarypeithes Hustache, 1939 , Opseobarypeithes Hustache, 1939 and Palaepus Hustache, 1939 . The first genus is listed in Sciaphilini Sharp, 1891 , the others in Peritelini Lacordaire, 1863 . From all these genera Basothorhynchus gen. n. can be easily distinguished not only by the free claws (it must be pointed out that some of these Kenyan genera have claws connected at their short bases), but mainly by the rostrum lacking laterally prominent pterygiae, the short scape, femora with a distinct tooth, the inner side of the tibiae sinuose and denticulate, and tibiae mucronate. In contrast, all genera from equatorial mountains have a rostrum with laterally prominent pterygiae, long scapes, adentate femora, inner sides of tibiae straight and not denticulate and tibiae amucronate. Basothorhynchus gen. n. is most similar to the genus Neomias Hustache, 1939 , known from the mountains of Ethiopia, Kenya, Uganda and Tanzania. This genus also has a rostrum with straight sides in dorsal view, without distinct pterygiae. But in all other characters Neomias shares the same distinguishing characters as Abarypeithes and similar genera.

Figures

FIGURE 1. Dorsal habitus of the male holotype of Basothorhynchus endroedyi sp. n.

FIGURES 2–11. Structural details of Basothorhynchus endroedyi sp. n. 2. head with rostrum, dorsal view; 3. head with rostrum, lateral view; 4. tergite VII and VIII in male; 5. femur and tibia of anterior right leg; 6. abdominal ventrites of female; 7. penis, dorsal and lateral view; 8. tegmen, dorsal view; 9. Sternite VIII of female, dorsal view; 10. ovipositor, dorsal view; 11. spermatheca. Scale bars: 1 mm (6), 0.5 mm (2–5, 7–11).