Rhinocoeta namaqua, Perissinotto, Renzo, 2019

Perissinotto, Renzo, 2019, Description of a new species of Rhinocoeta Burmeister, 1842 (Scarabaeidae, Cetoniinae) from the South African Northern Cape, ZooKeys 848, pp. 41-56 : 41

Rhinocoeta namaqua sp. nov. Figures 1, 3, 5

Diagnosis.

The two species can be separated mainly on the basis of the male parameres, which in R. namaqua lack the spine-like expansions on the apico-lateral margins that are so typical of the parameres of R. cornuta (compare Figs 3 and 4).The new species can also be recognised by the virtual absence of the depression behind the pronotal tubercle, which on the other hand is very prominent in R. cornuta , especially in the male (compare Figs 1 and 2). The pronotal tubercle of R. namaqua is very short and blunt in both sexes, with the apical surface virtually flat (Fig. 1A). Conversely, in C. cornuta this is generally quite elevated in the male and in both sexes the apex is generally smoothly rounded (Fig. 2A). Essentially in R. namaqua it is very difficult, if not impossible, to separate males from females on the basis of external morphology alone, as the pronotal tubercle is similarly reduced and the associated depression is lacking in both sexes. These characters are, on the other hand, key towards the separation of the sexes in R. cornuta .

Further to this, the two closely related species also exhibit differences at the level of the elytral costae three and five which, with some notable exceptions, are largely obsolete in most specimens of R. namaqua but still noticeable in R. cornuta , at least in the proximal two thirds of the elytra, above the apical umbone (compare Figs 1 and 2). Additionally, the body shape of R. namaqua is remarkably more globose and its average length larger than that of R. cornuta , i.e., 20.3-24.6 mm versus 12.5-22.5 mm ( Holm 1992, Beinhundner 2017), respectively.

Description of holotype male

(Figs 1 A–E, 3 A–C). Size. Length 22.2; width 14.1 mm.

Body. Completely black and generally matte, with small shiny areas restricted to elytral suture, basal portion of costae, humeral callus and peri-scutellar area (Fig. 1A); globose with dense sculpture throughout dorsal surface and short, scattered yellowish setae on dorsal periphery, becoming longer and denser on lateral margins (Figs 1A, C, D).

Head. Black with dense but coarse sculpture throughout surface and poorly elevated vertical, median ridge on frons; with medium to long yellow-brown setae on frons, eye canthus and antennal pedicel and basal margin; clypeus bilobate and deeply concave, with lateral margins elevated but straight posteriorly and smoothly rounded anteriorly; antennal clubs black to dark brown, of normal cetoniine length, slightly longer than flagellum; pedicel black but flagellum dark brown.

Pronotum. Completely black, matte and virtually semicircular in shape, with apically flat tubercle at anterior margin and smooth angles at postero-lateral margins, forming straight line in front of scutellum; peritubercular depression poorly developed and barely noticeable; small, scattered round punctures on disc, becoming larger, denser and more elongate towards lateral and anterior margins; short, scattered yellow-brown setae on lateral and anterior declivities, becoming longer and denser at all margins except posterior (Figs 1A, C).

Scutellum. Black, isoscelic triangular with sharply pointed apex and deep but narrow lateral grooves; with scattered round to elongate punctures across the surface and short setae on basal margin only (Fig. 1A).

Elytron. With costae barely visible and shiny around sutural, periscutellar area and two basal thirds of third and fifth costae; rest of surface matte and densely sculptured with round to vertically elongate punctures, becoming rugose on lateral and apical declivities; with short, erect tawny-coloured setae scattered regularly across whole surface, except periscutellar area and umbones; with apices smoothly rounded and matching perfectly at sutural joint, without significant gap or spinal projections; both humeral and apical calluses pronounced (Figs 1A, B).

Pygidium. Uniformly black, broadly elliptical with dense and fine rugose sculpture; with moderate central convexity and shallow, symmetric baso-lateral depressions; bearing thin, long setae along entire apical margin, with denser cluster around apical point.

Legs. Short and robust, with typical fossorial adaptations; tarsal segments moderately developed but tibiae thickened and expanded laterally, with several spurs, spines and denticles; protibia tridentate, with third tooth substantially reduced; mesotibia short, reinforced with mid outer ridge, three apical spines and two spurs; metatibia short but extremely robust, with supporting diagonal outer ridge, one hypertrophic spade-like spine and two thick spurs, with proximal spur hypertrophic and reaching half distance of total metatarsal length (Figs 1A, B, C); femora equally robust and expanded, reaching hypertrophy in metalegs.

Ventral surface. Black and shiny, but overwhelmingly covered in long, dense tawny-coloured setae, except on ventral side of femora, metasternum and abdominal sternites; exhibiting small and sparse round sculpture throughout surface; mesometasternal lobe smoothly rounded and poorly protruding anteriorly, with regularly spaced round punctures and thin setae emerging at their centre; abdominal sternites flat to very slightly depressed around middle.

Aedeagus. Parameres with dorsal lobes laterally expanded, covering completely ventral lobes in dorsal view (Fig. 3A); exhibiting constriction towards apical third, then expanding again at apex; apex flattening abruptly, with lateral corners sharp, but not exhibiting spinal protrusion (Figs 3A, B); duck-bill shaped and smoothly curved in lateral view (Fig. 3C).

Description of female.

Superficially, there is virtually no sexual dimorphism in this species, as its male lacks the deep depression around the pronotal tubercle, and the tubercle itself is normally short and blunt. This contrasts markedly with R. cornuta , where the male typically exhibits a well-developed tubercle (often hypertrophic) surrounded by a wide and deep depression on the anterior margin of the pronotum (Figs 2A, C, D). As a result, males and females of R. namaqua can only be separated by using a suite of secondary characters, especially the generally protruding pygidium and the slightly more convex abdominal sternites in the latter sex. The meso- and metatibial spurs are also substantially shorter in the female than in the male counterpart, particularly the proximal ones. The female is also more deeply and densely sculptured on the dorsal area, particularly on the pronotum, where small round punctures are uniformly distributed across its surface.

Distribution.

All known records are from areas situated above the South African Great Escarpment, in the Succulent and Nama Karoo biomes of the Northern Cape Province (Fig. 5). The specific bioregions included in its range are the Namaqualand Hardeveld, the Trans-Escarpment Succulent Karoo and the Upper Karoo, respectively ( Mucina and Rutherford 2006). Thus, the species appears to be a specialist of arid to semiarid environments.

Biology.

Larval development seems to be linked to sandy soils, generally in or around dry riverbeds or in alluvional or erosion deposits. Adults have often been collected in or under dung hills of herbivore mammals, including farmed goats and sheep. Its life cycle, therefore, appears to be similar to that of other, better-known members of the genus Rhinocoeta , e.g., R. sanguinipes ( Smith et al. 1998), although its larval stages remain undescribed. Adult activity seems to be restricted to the austral summer, from December to March, and emergence from the soil has been observed to be linked to rainfall events (pers. obs.). No adult specimen has yet been recorded feeding, either on flowers, fruits or tree sapping flows and, thus, it is almost certain that their period of adult activity may be very short and sustained only by energy reserves accumulated during larval development ( Smith et al. 1998, Perissinotto et al. 1999).

Derivatio nominis.

The species is named after the semiarid Namaqualand region of South Africa (Northern Cape Province), where most known specimens were collected.

Remarks.

There is no variability in the colouration within the series of specimens examined in this study. However, the elevation of elytral costae three and five varies substantially among specimens, with most exhibiting poorly elevated to obsolete costae, but a minority showing pronounced costae (e.g., paratype from De Aar). Within the type series, the size ranges as follows: ♂ length 20.3 - 24.2 mm, width 13.2 - 14.4 mm (n = 10); ♀ length 23.3 - 24.6 mm, width 13.4 -14.6 mm (n = 6).

Type material.

Holotype (♂): South Africa, NC, Goegap Nat Res, 30 Dec 1996, R Perissinotto & L Clennell (ISAM). Paratypes: 5♂♂ + 4♀, as above (BMPC); 1♂, South Africa, Northern Cape, Sutherland, Swaarweerberg 1683 m, 32°23'50.1"S, 20°34'39.3"E, 01 Jan 2008, AP Marais leg (BMPC); 3♂♂ + 2♀, South Africa, NC, Kamieskroon, 26 Jan 2018, R Perissinotto & L Clennell; 1 ind, South Africa, Northern Cape, Anenous, Namaqualand, 01/01/1911, CL Biden leg (ISAM: COL-A027336); 1♀, S.W. Africa, De Aar (50 milles au N d’Upington), 7-III-1950, H-J Brédo (ISNB: R.I.Sc.N.B., I.G. 18.284) [Reference to SW Africa and distance from Upington most likely erroneous; A Drumont, pers. comm.].