Relictorygmus riparius Bilton & Mlambo 2024, sp. nov.
Creators: name: Bilton, David T.
name: Mlambo, Musa C.
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Hydrophilidae
Relictorygmus
Relictorygmus riparius

description: Relictorygmus riparius sp. nov.
(Figs. 1–4)
Type locality. South Africa, Northern Cape Province, Kamiesberg, stream beside dirt road from De Kruis to Leliefontein, 30° 21’ 37.39” S 18° 07’ 01.13” E, 1168 m (Fig. 4A).
Type material. Holotype (male): “ 18/ix/2023 South Africa NC// Kamiesberg —stream beside// road from De Kruis to Leliefon // -tein 302137.39S 180701.13E// 1168 m D T Bilton leg.” and red holotype label (AMG).
Paratypes (5): 2♂, 3♀ same data as holotype (AMG, CDTB, NMPC, NMW).
Description. Size: Holotype: BL 5.80 mm; EL 3.80 mm; EW 03.20 mm. Paratypes: Male BL 5.20–5.30 mm; EL 3.30–3.45 mm; EW 3.05–3.15 mm. Females BL 6.30–6.40 mm; EL 4.05–4.25 mm; EW 3.30–3.45 mm.
Colour: Dorsum (Fig. 1A) dark brown to black; pronotal margins paler, reddish brown. Antennal stem and maxillary and labial palpi and yellowish brown, antennal club darker; legs reddish brown, tarsi paler. Venter (Fig. 2) reddish brown; underside of head and metaventrite darker.
Head: Labrum (Fig. 1A & C) strongly transverse; anterior margin with broad, shallow emargination; dorsal surface shining, microreticulation absent, with sparse, fine punctation, punctures bearing long, fine adpressed setae in basal half. Clypeus, frons and vertex shining; without microreticulation, with sparse, shallow, medium punctures bearing short, peg-like sensillae.Compound eyes moderately large; inter-ocular distance approximately 5x transverse diameter of eye. Maxillary palpi moderately long, last palpomere cylindrical, penultimate widened apically.
Pronotum: Transverse, widest at base (Fig. 1A). Anterior margin strongly emarginated, emargination sinuate in centre; posterior margin strongly bisinuate around centre; lateral margins strongly arcuately rounded. Anterior and posterior angles obtusely rounded. Surface strongly shining; microreticulation absent, with sparse, shallow, medium punctures bearing short, peg-like sensillae as on frons.
Elytra: Slightly elongate (Fig.1A); sides strongly arcuate, from shoulders to posterior angles.Ten seriate puncture rows, punctures slightly wider than punctures in intervals. Sutural puncture row striate impressed, particularly in posterior half (Figs 1A & 3A). Serial and interval punctures mostly relatively small and shallow; systematic punctures markedly larger and distinct (Fig. 3A). Highest towards rear of elytra; dorsal profile following a single arc in lateral view (Fig. 1B).
Venter: Mentum (Fig. 2B) with broadly truncate, dorsally-directed apicomedian projection anteriorly; broad, transverse depression posterior to projection, deepest anteriorly, boundary between the two areas appearing as a transverse ridge; surface shining, with sparse, shallow, medium punctures basolaterally. Submentum (Fig. 2B) shining; smooth anteriorly, somewhat rugose posteriorly, with medium, shallow punctures throughout, each bearing a long, yellow-white arcuate seta. Genae shining, microreticulation absent. Gula shining, rugose; punctate and setose as submentum; median ridge present posteriorly. Prosternum (Fig. 2C) coarsely microreticulate and rugosely punctate, punctures bearing long, arcuate yellow-white setae; posterior marginal bead broader than anterior, microreticulate; anterior and posterior marginal beads lacking punctures and setae. Mesoventrite (Fig. 2D–E) angulate, reaching coxal cavities laterally; elevated anterior part subtriangular with weakly sinuate posterior margin; main part rugosely punctate and setose medially; lacking transverse groove posteromesally. Raised median area of metaventrite (Fig. 2F) setose anteriorly and smooth and impunctate posteriorly, with clear longitudinal furrow. Anterior metaventral process wide, triangular, ca. 1.3× as long as maximum width.
Legs: Ventral surface of profemora (Fig. 2G) moderately pubescent at base, particularly posteriorly, with very sparse, scattered setae to apex. Meso- and metafemora (Figs 2H–I) sparsely pubescent throughout.
Aedeagus: Elongate (Fig 1D). Phallobase rather weakly constricted basally; narrow basal part much shorter than broader anterior portion. Parameres shorter than phallobase, with outer faces arcuate basally, then straight and converging to truncately rounded apices; inner margins weakly arcuate. Median lobe relatively broad, not reaching paramere apices; tapering to truncately rounded apex over distal half; median strut relatively broad. Gonopore apex expanded, slightly subapical.
Female: Without obvious external differences to males.
Differential diagnosis.
In overall habitus and structure of the genitalia and most external characters, the new species most closely resembles R. trevornoahi. In common with this species, the ventral surface of the profemora is sparsely pubescent (Fig. 2G), rather than densely pubescent at base as in R. repentinus. It does, however, differ from this species in a number of ways, which are summarised here. The dorsal punctation of R. riparius sp. nov. is finer and shallower than that of R. trevornoahi. This means that the systematic punctures of the elytra are more clearly distinguishable from background punctation in R. riparius sp. nov. In addition, the serial punctures are more markedly striateimpressed in R. trevornoahi compared to the new species (Fig. 3). The excavation on the mentum is deeper and narrower in R. riparius sp. nov. when compared with R. trevornoahi. The prosternum of the new species (Fig. 2C) is also more setose and rugose, the raised anterior portion of its mesoventrite is triangular (Fig. 2D–E) as opposed to heart-shaped and its mesoventrite (Fig. 2D) lacks an obvious transverse groove posteromesally. The punctation on the ventral face of the femora of R. trevornoahi is denser, with coarser setae, than in the new species (Fig. 2G–I). Lastly, the aedeagus differs from both previously described species in a number of details, including the relative lengths and shape of the different elements (Fig. 1D–F).
Etymology. Named in reference to the habitat, at the banks of a small mountain river.
Distribution and ecology. Known only from the type locality (Fig. 4), beside a small mountain river in the Kamiesberg, Northern Cape Province, South Africa. Beetles were found living in mats of wet moss, immediately beside the stream at the time of sampling, and within areas of seasonal seepage on peaty soil (Fig. 4A). They were revealed when moss was removed and wetted, allowing them to float free of the microhabitat. At the time of collection it was assumed that this was a species of Coelostoma, meaning many additional specimens (at least 10) were released. The only other beetle present in this microhabitat was Anacaena glabriventris Komarek, 2004. The limited hydrofuge pubescence on the femora suggests that the respiratory bubble of R. riparius sp. nov. is relatively small.
description: Published as part of Bilton, David T. & Mlambo, Musa C., 2024, A new, apparently lotic species of Relictorygmus from the Northern Cape Kamiesberg, South Africa (Coleoptera, Hydrophilidae, Cylominae), pp. 143-150 in Zootaxa 5448 (1) on pages 144-147, DOI: 10.11646/zootaxa.5448.1.10, http://zenodo.org/record/11231037