Prosthetops wolfbergensis, Bilton, David T., 2013

Bilton, David T., 2013, Prosthetops wolfbergensis sp. nov. — a giant amongst the ‘ minute moss beetles’, with new data on other members of the genus (Coleoptera, Hydraenidae), Zootaxa 3666 (3), pp. 345-357 : 346-354

Prosthetops wolfbergensis sp. nov.

( Figs 1–10 )

Type locality. South Africa, Western Cape, Cederberg mountains, rockpool below Wolfberg Arch, nr. Gabriel’s Pass, 1,500 m, D.T. Bilton leg. ( Fig 10 A).

Type material. Holotype (male): “ 23/ix/2011 South Africa WC, Cederberg—rockpools below Wolfberg Arch nr Gabriel’s Pass, 1,500 m, D T Bilton leg.” (genitalia extracted and mounted on same card) and red holotype label (SAM).

Paratypes (73): South Africa: 16 3, 12 Ƥ “ 23/ix/2011 South Africa WC, Cederberg—rockpools below Wolfberg Arch nr Gabriel’s Pass, 1,500 m, D T Bilton leg.” (CDTB, MCZ, NMPC, NMW, OUMNH, SANC); 2 3 “ 23/ix/2012 South Africa WC, Cederberg- rockpools below Wolfberg Arch @ 1,400 m, D T Bilton leg.” (CDTB); 4 3, 4 Ƥ “ 23/ix/2012 South Africa WC, Cederberg- rockpools below Wolfberg Arch, D T Bilton leg. (CDTB, CTV); 4 3, 1 Ƥ “ 20/ix/2010 South Africa WC, Cederberg rockpool @ Stadsaal Cave ca. 3km SW of Matjiesrivier, D.T. Bilton leg.” (CDTB); 10 3, 6 Ƥ “ 23/ix/2011 South Africa WC, Cederberg—stream with seeps over rock @ 1,200 m, below Wolfberg Arch, D.T. Bilton leg.” (CDTB, SAM, TMSA)—specimens from seepage over gently sloping rocks beside stream; 5 3, 2 Ƥ “ 23/ix/2012 South Africa WC, Cederberg—stream with seeps, below Wolfberg Arch nr. Die Boog, 1,200 m, D.T. Bilton leg.” (CDTB)—specimens from seepage over gently sloping rocks beside stream; 2 3 “ 24/ix/2011 South Africa WC, Cederberg—waterfall and stream above Algeria, below Middelberg, D.T. Bilton leg.” (CDTB); 13 “ 23/ix/2012 South Africa WC, Cederberg stream on Wupperthal road 2 km S of Eselbank, D.T. Bilton leg.” (CDTB); 1 3, 1 Ƥ “ 20/ix/2010 South Africa WC, Middelberg—roadside pool on sand beside 303 road ca. 5 km S of Kunje, D.T. Bilton leg.” (CDTB)—specimens from seepage over gently sloping rocks beside pool; 1 3 “ 22/ix/2010 South Africa WC, stream along road to Towsrivier from 303, 5 km N of Gydopas, D. T. Bilton leg.” (CDTB); 3 3, 1 Ƥ “ 18/ix/2010 South Africa NC, Temporary pools on R27 road ca. 2 km E of Vanrhyspas—pools on sandy soils, D. T. Bilton leg.” (CDTB). All with red paratype labels.

Description. Size: Holotype: body length (front of labrum to elytral apices) 3.35 mm; max. width (elytra) 1.2 mm. Dorsum ( Fig. 1 — paratype) black with aeneous reflections, raised intervals in front of and behind elytral saddle less aeneous and darker black than remainder of elytron, giving a somewhat spotted appearance. Legs light brownish-red, tarsi and femoro-tibial junctions darker, piceous to black. Mid femora distinctly paler. Venter predominantly dark piceous, with silvery hydrofuge pubescence.

Head: Length from labroclypeal suture to posterior carina 0.8x distance between eyes. Eyes large and protuberant, occupying>1/2 length of head as measured between labroclypeal suture and posterior carina. Dorsal surface of head weakly shining, but lacking microreticulation. Sparsely punctate with small fine punctures, each of which bears a fine recumbent seta ( Figs 3 A & 4A). Frons with a central elevation, broken by a slightly elongate concavity between the ocelli, and arcuate sulci running from just in front of each ocellus towards the lateral corners of the frontoclypeal suture ( Figs 1 A & 3A). Frons depressed and somewhat rugose around interior margins of eyes, creating the impression of an arcuate ridge between this region and the inner arcuate sulci. Frontoclypeal suture well impressed and bisinuate. Clypeus strongly transverse and laterally emarginate. Labrum strongly produced, markedly wider than clypeus, and approximately 2.5x its length, with arcuate sides and strongly reflexed anterior angles and margins ( Fig. 4 A). Labrum with strong, V-shaped apicomedial notch, ca. 1/3 length of plate, and rounded, rectangular anterior angles.

Pronotum: Distinctly cordate, widest just before middle ( Figs 1 A & 3A). Anterior margin weakly bisinuate, almost arcuate, with very narrow hyaline border in middle 1/3. Posterior margin clearly bisinuate, central portion with a narrow band of strongly transverse microreticulation. Sides weakly denticulate, with slight, interrupted margination. Lateral depressions more strongly marked at front and hind ¼ of depression length; almost pit-like anteriorly, and more elongate posteriorly. Median groove interrupted in posterior half. Posteroadmedian fovea deep, especially posteriorly; opening anteriorly. Much of pronotal surface with very fine, sparse punctures bearing fine recumbent setae, as on frons. In addition, anterior and posterior ¼ with moderately fine, larger, deeper punctures between lateral depressions, which also bear recumbent setae. Larger punctures also present in median groove and posteroadmedian fovea, which appear rugose between punctures. Pronotal surface moderately shiny, with at most a trace of obsolete microreticulation on lateral areas (with exception of hind margin as indicated above). Scutellum with strong, well impressed, slightly transverse microsculpture.

Elytra: Elongate, somewhat parallel-sided, and widest just behind middle ( Fig. 1 A). Sides weakly explanate; minutely crenulated posteriorly. Elytral apices separately rounded to a marked central notch. Each elytron with 10 rows of serial punctures situated in grooves; series 9–10 confluent in the same groove. Grooves which bear serial punctures particularly well marked laterally and posteriorly, where intervals appear elevated as a consequence. Series 2–3 irregular at middle, where elytra are distinctly depressed or ‘saddled’. Elytral intervals with fine, sparse punctures bearing fine recumbent setae, which are longer than those on head and pronotum, and longer towards the lateral and apical margins. In addition, longer sensory setae are present apically on intervals 5, 7 and laterally on interval 10. Elytra shiny, with traces of obsolete, isodiametric reticulation, this being most obvious on disc in front of and immediately behind the saddle.

Venter: Mentum microreticulate around all margins; microreticulation transverse at front margins and almost isodiametric elsewhere. Mentum with scattered coarse punctures, each bearing a stiff seta, these being longer towards front angles. Submentum with similar punctures and setae on front half, and obsolete, isodiametric reticulation. Genae rugulose. Areas between hind margin of eyes and postocular carinae transversely rugose. Posterior gular pits deep and rounded; cuticle transversely rugose behind and to the sides of these. Postocular antennal pocket well developed, with dense hydrofuge vestiture. Wet hypomeron of pronotum, and elytral pseudepipleura smooth and shining; lacking microreticulation. Pronotal wet hypomeron with very sparse fine punctures, with fine recumbent seta. Pro- meso- and metathoracic sterna with dense silvery hydrofuge vestiture, with the exception of narrow, elongate mesosternal plaques and lateral metasternal carina, which are smooth and shining. Abdominal ventrites 1–4 with dense hydrofuge vestiture, which is also present on the anterior ½ of ventrite 5. Posterior half of ventrite 5, whole of ventrite 6 and terminal ventrite lacking vestiture. Ventrites 5 and 6 dull and densely microreticulate. Ventrite 6 with fine scattered punctures bearing recumbent setae. Terminal ventrite shining, with open transverse microreticulation and coarse punctures, each bearing short stiff setae. Posterior borders of ventrites 1–4 with a row of closely-set, long golden setae ( Fig. 5 A).

Legs: Meso- and metacoxae with stout, spiny golden setae, the arrangement of these on the metacoxae being characteristic ( Fig. 5 A). Similar, but shorter and sparser setae present on meso- and metatrochanters ( Fig. 5 A). Similar, but more elongate setae present on ventral side of meso- and metafemora; these setae being adpressed into depressions of the femoral cuticle. Mesotibia thickened and curved in distal 1/3, with stout setae ( Fig. 6 A). Protarsomeres 1–4 with small, stout ambulatory setae on their ventral faces. Distal protarsomere elongate, thickened towards apex and enlarged at the base of two large, spiny, distally-directed setae; claws curved and elongate; ½ length of distal segment ( Fig. 7 A). Mesotarsomeres 1–3 with short, stout ambulatory setae. Mesotarsomere 4 enlarged and subquadrate, with two stout, characteristically shaped and oriented setae; the proximal ventrally, the distal distally directed; distal segment arcuate and elongate, with long adpressed, sensory setae; claws elongate, ca.1/3 length of distal segment ( Fig. 8 A).

Aedeagus: Elongate, with parameres attached near base, and extending beyond apex of main piece. Paramere apices flattened and expanded, with broadly rounded external margins, and long setae. Main piece characteristically shaped, with asymmetrical dorsomedial tooth and field of long setae in centre, below apex. Distal lobe tubular and asymmetrical, with broad, trumpet-like opening; extending slightly beyond apices of parameres ( Fig. 9 A).

Female ( Fig. 2 A): Entire dorsal surface of head and pronotum rugosely microreticulate, with isodiametric meshes. Reticulation deeply impressed, resulting in a dull, granulate appearance. Labrum less pronounced and shorter than in male. Frons flatter and less elevated. Concavity between ocelli shorter and more rounded; arcuate sulci anterior to ocelli much shorter, resembling elongate pits which open anteriorly. Lateral margins of pronotum more distinctly toothed, elytral lateral margins also, but less so. Elytra flatter, and broader, with more deeply impressed longitudinal grooves and a deeper saddle. Explanate elytral margins much broader. Setae of head, pronotum and elytra denser, and longer and thicker than those in male, resulting in a much more obviously setose appearance. Mentum more strongly setose than in male. Wet hypomeron of pronotum with granular reticulation. Glabrous portion of ventrite 5 broader and more semicircular. Setae present on meso- and metacoxae and trochanters, but much smaller and fewer than in male.

Variation: Specimens of P. w o l f b e rg e n s i s sp. nov. vary considerably in body size. The largest male from the Cederberg measures 3.45 mm from the front of the labrum to the elytral apex, and 4.2 mm from the front of the labrum to the abdominal apex, when the latter is extended as in life. In contrast the smallest male known, from the Middelberg, reaches only 2.35 and 2.8 mm in these dimensions, respectively. Females range from 2.9–3.45 mm (front of labrum—elytral apex) and from 3.05–4.15 mm (total length, including abdomen). Females also vary somewhat in the width of the explanate margins of the elytra, but never have these as broad as in most P. pronotus examined (see below).

Differential diagnosis. The new species is clearly a member of the P. megacephalus group (sensu Perkins & Balfour-Browne, 1994) sharing external and aedeagal characteristics with known species. P. wolfbergensis sp. nov. has the head slightly narrower than the pronotum, which is 1.05–1.1x as wide as the head, resembling P. pronotus Perkins & Balfour-Browne, 1994 in this regard, but with a much more cordiform, arched and rounded pronotum ( Figs 1 & 3 ), giving an appearance superficially more like P. setosus Perkins & Balfour-Browne, 1994 , especially in males. Additionally, in the case of males, the new species is smooth and relatively shiny over the entire dorsal surface, lacking microreticulation on the head and pronotum, which is in contrast markedly developed in P. pronotus ( Fig. 4 ). Male leg modifications and genitalia are also characteristic, including pro- and mesotarsal chaetotaxy, here illustrated for the first time for all species of the P. megacephalus group ( Figs 7–8 ). The new species most closely resembles P. pronotus in the structure of the mesotibiae, meso- and metacoxae and trochanters, and the aedeagus (see Figs 5–6 & 9 ). The mesotibia of both P. pronotus and P.wolfbergensis sp. nov. lack the internal fringe of long setae, which is present in both P. megacephalus (Boheman, 1851) and P. setosus ( Fig. 6 ). The short golden setae of the meso- and metacoxae and trochanters are relatively short in P. pronotus and P.w o l f b e rg e n s i s sp. nov., and longer in both P. megacephalus and P. setosus ( Fig. 5 ). Compared to P. pronotus , females of P. wolfbergensis sp. nov. have a broader, more arched and cordiform pronotum, and elytra usually with less strongly explanate side margins ( Fig. 2 ).

Distribution. Known from parts of the Western and Northern Cape regions of South Africa, from the area around Gydopas north of Ceres, through the Cederberg and Middleberg mountains, north to the western edge of the Great Escarpment close to Vanrhyspas. Probably widespread in suitable rockpool habitat in intervening areas. The known distribution is more northerly than that of P. pronotus , its closest morphological sibling, but is at least partly sympatric with P. setosus , which, whilst apparently much rarer in the region, overlaps with the new species in the Cederberg; the two species having been found in the same rockpool on one occasion.

Etymology. Named after the Wolfberg Arch, a striking geological feature of the Cederberg range, in whose shadow this species was abundant.

Ecology. Most specimens are from temporary rain filled rockpools on montane plateau ( Fig. 10 ), where the species has been observed feeding on biofilms as both adults and associated (and presumed conspecific) larvae, which, like adults, were fully aquatic. At Stadsaal Cave adults were initially collected from a large, more permanent rockpool ( Fig. 10 C) on 20/ix/2010, when smaller pools close by ( Fig. 10 B) were dry. Heavy rains on 21/ ix/2010 meant these smaller pools filled with rainwater, and numerous larvae and adults were observed grazing biofilms by that evening, suggesting that both adults and larvae are capable of surviving in the bed of apparently dry pools. The beetle was also abundant on a gently sloping seepage face beside a stream below Wolfberg Arch, where adults were observed grazing biofilms. P. wolfbergensis sp. nov. has also been taken from similar seepage habitats beside sandy temporary pools (edge of the Great Escarpment at Vanrhyspas), from a pool in river shingle (Matjiesrivier), and on river stones ( Algeria & Towsrivier). It is not clear whether these last two sites represent typical habitats, however, as the species was rather scarce on both occasions.

Figures

FIGURE 1. Habitus of Prosthetops males. A) P. w olf bergen sis sp. nov., paratype; B) P. pronotus; C) P. megacephalus; D) P. setosus. Scale bar = 1 mm.

FIGURE 2. Habitus of Prosthetops females. A) P. w ol fbergen si s sp. nov., paratype; B) P. pronotus. Scale bar = 1 mm.

FIGURE 3. Head and pronotum of Prosthetops males. A) P. wolfbergensis sp. nov.; B) P. megacephalus; C) P. pronotus; D) P. setosus.

FIGURE 4. Clypeo-labral region of Prosthetops males. A) P. w o l f b e rg e n s i s sp. nov.; B) P. megacephalus; C) P. pronotus; D) P. setosus.

FIGURE 5. Metacoxae and metatrochanters of Prosthetops males. A) P. wolfbergensis sp. nov.; B) P. megacephalus; C) P. pronotus; D) P. setosus.

FIGURE 6. Mesotibiae of Prosthetops males. A) P. wolfbergensis sp. nov.; B) P. megacephalus; C) P. pronotus; D) P. setosus.

FIGURE 7. Protarsi of Prosthetops males. A) P. w o l f b e rg e n s i s sp. nov.; B) P. megacephalus; C) P. pronotus; D) P. setosus.

FIGURE 8. Mesotarsi of Prosthetops males. A) P. wolfbergensis sp. nov.; B) P. megacephalus; C) P. pronotus; D) P. setosus.

FIGURE 9. Aedeagal apices of Prosthetops males. A) P. wolfbergensis sp. nov.; B) P. megacephalus; C) P. pronotus; D) P. s e t o s u s.

FIGURE 10. Habitats of P. wolfbergensis sp. nov., Cederberg range, Western Cape, South Africa A) type locality, rockpool below Wolfberg Arch; B) small rockpools nr. Stadsaal Cave, (pools were completely dry one day earlier, when pool in C) was photographed; C) large rockpool nr. Stadsaal Cave. Photos D T Bilton.