Ochthebius mlamboi, Bilton, 2021

Bilton, David T., 2021, Differentiation of South African coastal rock pool Ochthebius is associated with major ocean currents (Coleoptera: Hydraenidae), Acta Entomologica Musei Nationalis Pragae (Acta. Ent. Mus. Natl. Pragae) 61 (1), pp. 253-260 : 257-259

Ochthebius mlamboi sp. nov.

( Figs 1B, D , 2B, D )

Type material. Hඈඅඈඍඒඉൾ:J ‘ 9/ix/2019 SouthAfrica EC/ Mkambati Nature Reserve/ supralittoral rock pools below Point Cottage/ 31°19’09.08”S 29°58 20.46”E, 3 m / AMG Loc. 218 D T Bilton leg.’ ( AMGS). With red holotype label. Pൺඋൺඍඒඉൾඌ:13 JJ 10 ♀♀ ( AMGS, CDTB, NHMW, NMPC, SAMC) same data as holotype; 3 JJ 2♀♀ ( CDTB) ‘ 23/ix/2008 South Africa EC/ Tsitsikamma Storms River/ Mouth rockpools/ D T Bilton leg.; 1 J 1 ♀ ( CDTB) 21/ix/2009 South Africa EC/ Tsitsikamma NP waterfall pools ca./ 3.5 km along Otter Trail W of Storms/ River Mouth D T Bilton leg.’; 10 JJ 3 ♀♀ ( CDTB) ‘ 21/ix/2008 South Africa WC/ Plettenberg Bay rockpools/ D T Bilton leg.’; 1 J ( CDTB) ix/2017 South Africa EC/ Sea View ca. 6 km W of Port Elizabeth/ rockpools D T Bilton leg.’; 1 J 2 ♀♀ ( NHMW) ‘ RSA: Eastern Cape, 6.3.1997 / Tsitsikamma Mts./ 40km E Plettenberg Bay/ 34 ° 05ꞌ S 23° 21 ꞌ E/ leg. Hess & Heckes (19)’; 4 ♀♀ ( NHMW) ‘ RSA, Eastern Cape Tsitsi-/ kamma Mts: 40km E Pletten-/ berg Bay, 2km E Storms Ri-/ ver Mouth, bis 30m NN./ 6.3.1997 Hess/Heckes leg.’; 108 spec. ( MCZH, NHMUK) ‘S. AFRICA:/ Knysna Heads./ 16.iii.1954.// in rock-pools of/ splash-zone// J. Balfour-Browne/ Brit. Mus. 1954-797// Ochthebius / capicola/ (Peringuey)/ Det. P. D. Perkins’; 33 spec. ( NHMUK) ‘S. AFRICA:/ Knysna Heads./ 16.iii.1954.// in rock-pools of/ splash-zone// J. Balfour-Browne/ Brit. Mus.1954-797’; 22 spec. ( MCZH, NHMUK) ‘S. AFRICA:/ Skoermakerskop,/ nr.Port Elizabeth./ vi. 1959 / B. R. Stuckenberg.// Ochthebius / capicola/ (Peringuey)/ Det. P. D. Perkins’. All with red paratype labels.

Description. Size: Holotype: BL 1.95 mm; EL 1.15 mm; EW 0.80 mm. Paratypes: JJ BL 1.90–2.00 mm; EL 1.10–1.15 mm; EW 0.80–0.85 mm. ♀♀ BL 1.80–2.05 mm; EL 1.05–1.20 mm; EW 0.75–0.85 mm.

Colour: Dorsum ( Fig. 1B ) brown to blackish, with greenish to coppery aeneous reflections, these sometimes covering most of upper surface with exception of lateral margins of pronotum, lateral and apical areas of elytra, exposed mandible margins and labral apex, these areas being paler. Legs testaceous to brown; maxillary palpi and basal antennomeres yellow to pale testaceous, club segments darker. Venter piceous; palpifer and pronotal hypomeron paler.

Head: Labrum slightly transverse, broadly rounded laterally with straight, slightly thickened and raised apical margin, particularly in centre; sides and apex minutely serrate. Surface of labrum dull, microreticulate, meshes isodiametric to slightly transverse; with sparse-moderate, medium punctures, bearing white, decumbent setae. Frontoclypeal suture distinct, arcuate, becoming weaker laterally. Clypeus, frons and vertex somewhat dull with aeneous reflections; with somewhat rugulose microreticulation of mostly isodiametric meshes and sparse-moderate, medium punctures bearing long, white, decumbent setae; reticulation especially strong on frons and vertex, becoming transverse on posterior vertex and occiput, here absent centrally. Interocular foveae shallow, relatively small, but abrupt. Ocelli obsolete, shining, reduced to patches approx. 2–4 reticulation meshes in size and not distinctly raised. Compound eyes moderately sized, occupying approx. 0.4 side of head, 8–10 ommatidia in longest series.

Pronotum: Widest just behind anterior angles, then gradually attenuate to posterior angles ( Fig. 2B ). Anterior margin broadly but very shallowly arcuate over median 0.7; posterior margin rounded; lateral margins straight behind widest point, anteriorly arcuate to anterior angles. Anterior and posterior angles obtusely rounded, the latter more so. Anterior and posterior margins with distinct hyaline border; lateral margins with narrower hyaline border from just behind widest point to posterior angles, becoming broader posteriorly and continuous with hyaline edge of posterior margin. Surface weakly shining, with aeneous reflection, especially on disc; strongly microreticulate, with isodiametric to slightly transverse meshes; meshes distinct in lateral areas, outside lateral depressions; entire surface with sparse, fine punctures bearing long, white, recumbent to decumbent setae. Irregular row of larger punctures, bearing long, white suberect setae along anterior margin each side of median emargination. Disc with very shallow, almost obsolete transverse impressions in front of and behind middle. Lateral depressions shallow, broad, expanded anterolaterally and nearly reaching anterior angles; shallowly, subrugosely punctate.

Elytra: Elongate oval, broadest anteriorly; weakly curved to almost subparallel over anteromedian 0.3, then weakly attenuated to separately rounded hind angles. Anterior angles broadly rounded; shoulders distinct. Lateral margins very narrowly explanate. Elytral punctures random, no trace of longitudinal series. Punctures ( Fig. 2D ) moderately dense, moderate in size and relatively shallow, particularly posteriorly; all bearing long, white, recumbent setae. Interstices flat, with microreticulation mostly restricted to shallow transverse channels; more shining than head and pronotum, with aeneous reflection.

Legs: Relatively elongate, metatibial length slightly less than pronotal width. Protarsomeres 1–2 slightly widened and with pad of suction setae.

Venter: Mentum, submentum, and genae shining, microreticulation restricted to transverse ridges on outer areas of genae; mentum and submentum with sparse, fine punctures, bearing fine, white decumbent setae. Gula with dense, fine to medium punctures bearing short recumbent setae; surface shining between punctures, but overall appearance at low magnification dull. Antennal pockets well developed. Prosternum rugosely microreticulate and punctate, punctures bearing long, erect to recumbent setae which form part of the hydrofuge vestiture; mesoventrite same, but reticulation and punctures less impressed and dense, and vestiture sparser. Pronotal hypomeron broad, wet hypomeron shining, glabrous; hypomeral antennal pocket well developed. Elytral epipleurs broad anteriorly, narrowing gradually to ca. 0.2 from apex; surface shining, with sparse, scattered setae and narrow strip of hydrofuge vestiture interiorly over anterior 0.3; row of short, curved setae running along edge of narrow posterior 0.2. Metaventrite with isodiametric to transverse microreticulation, stronger at sides, somewhat obsolete in centre; with dense, fine punctures bearing shaggy hydrofuge vestiture; vestiture often rubbed off in central area. Abdominal ventrites 1–5 completely and 6 laterally with slightly transverse, rugulose microreticulation and densely hydrofuge pubescent; ventrite 6 medially sparsely pubescent, shining; apical 0.8 entirely without vestiture, apical 0.5 of glabrous area devoid of microreticulation and punctures, strongly shining. Apical tergum sharply rounded, with tuft of long flagelliform setae on each side and few spiniform setae.

Aedeagus: Elongate ( Fig. 1D ), main piece curved in lateral view; strongly curving to the right in ventral view. Apex of main piece bluntly pointed in lateral and ventral views. Distal lobe narrow, elongate, sinuous. Parameres inserted close to base; elongate, narrow, curved as main piece in lateral view; apices slightly expanded, rounded in ventral view.

Female: Differs from the male in the following characters: labral margin not so strongly raised; lateral setae of mandibles smaller; explanate elytral margin broader; median 0.3 of ventrite 1 reduced to narrow, membranous strip, sternum on each side appearing somewhat triangular; apical tergum more angulately rounded, long setae curling away from midline and spiniform setae slightly more numerous; protarsomeres narrower, without suction setae; many with elytra somewhat paler than in males, particularly laterally and apically.

Variation. In addition to small variations in size, specimens vary in colouration, some being paler than the individual illustrated, particularly on the elytra. There is also some variation in the strength of elytral reticulation, specimens examined from the western part of the known range (Port Elizabeth, Tsitsikamma and Plettenberg Bay) having slightly stronger reticulation than those from the type locality. The aedeagus shows little variation in size and overall appearance, but some individuals examined have shorter distal lobes than illustrated, this variation being observed amongst specimens collected from the same locality.

Differential diagnosis. Despite resembling O. capicola , the new species can be distinguished from it on both external and genitalic characters. Firstly, O. mlamboi sp. nov. is smaller than O. capicola (TL 1.80–2.05 mm vs. 1.95– 2.95 mm, respectively – see Figs 1A & B ); a difference which, despite some overlap, is usually apparent even with the naked eye. Ochthebius mlamboi sp. nov. has pronotal reticulation ( Fig. 2B ) formed of distinct, typically isodiametric meshes throughout the disc, very different from the finely rugulose reticulation seen in O. capicola ( Fig. 2A ). The pronotum of O. capicola also differs in the corrugated surface of the areas outside the lateral depressions, in which reticulation is not visible; meshes here being clear in O. mlamboi sp. nov. The elytral punctation of the two species also differs significantly ( Figs 2C & D ); whilst both have a random pattern of punctation, the punctures of O. capicola are denser and deeper than those of O. mlamboi sp. nov., particularly on the disc. The interstices of O. mlamboi sp. nov. have sparser and less impressed microreticulation channels than in O. capicola . There are also slight differences in the sculpture of abdominal ventrite 6, which has a relatively larger glabrous patch in O. mlamboi sp. nov. Lastly, the aedeagi ( Figs 1C & D ) of the two species differ; that of O. capicola is larger (main piece length 0.58–0.60 vs. 0.52–0.54 mm), has a main piece which curves more abruptly apically, and has a more finely pointed apex. A specimen from Mkambati exhibited ca. 5% divergence in mitochondrial COI sequence from individuals of O. capicola from Yzerfontein and Simons Town (I. Ribera, pers. comm.). For separation of O. mlamboi sp. nov. from O. rubripes , see under O. capicola .

Etymology. Named for my friend and colleague, Dr Musa C. Mlambo, Albany Museum, Grahamstown, SouthAfrica, who assisted with the collection of part of the type series; in recognition of many enjoyable joint field trips.

Distribution and ecology. The new species is apparently widely distributed on the southern and southeast coasts of South Africa, being known to date from Mkambati in the East to Plettenberg Bay in the west ( Fig. 3 ). The species is apparently replaced by O. capicola from the west coast of False Bay northwestwards, but both the western and northeastern limits of its distribution will need to be confirmed by future fieldwork. As with a number of other coastal taxa, the boundary between the two species may be situated in False Bay (see Discussion). All specimens have been collected from supralittoral rock pools, as with O. capicola .

Figures

Fig. 1. Ochthebius species. A – O. capicola (Péringuey, 1892) (Yzerfontein, Western Cape Province), male habitus; B – O. mlamboi sp. nov., holotype habitus; C – O. capicola (Péringuey, 1892) (Yzerfontein, Western Cape Province), aedeagus, lateral and ventral views; D – O. mlamboi sp. nov., holotype aedeagus, lateral and ventral views. Scale bar A–B = 1 mm; C–D = 0.25 mm.

Fig. 2. Ochthebius species, showing dorsal sculpture A & C – O. capicola (Péringuey, 1892) (Yzerfontein, Western Cape Province); B & D – O. mlamboi sp. nov. A & B – pronota; C & D – elytra. Scale bars = 0.5 mm.

Fig. 3. Distribution of material examined, with approximate positions of major ocean currents. Red symbol – O. capicola (Péringuey, 1892); blue symbol – O. mlamboi sp. nov.