Anacaena fosteri Bilton, Mlambo & Balke, 2025, sp. nov.
Creators: name: Bilton, David T.
name: Mlambo, Musa C.
name: Balke, Michael
Publisher: name: Zenodo
Year: 2025
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Hydrophilidae
Anacaena
Anacaena fosteri

description: Anacaena fosteri sp. nov.
(Fig. 1)
Type locality. South Africa, Western Cape Province, Cederberg, Die Vlei along headwaters of Driehoek River, 943 m, waterlogged algal covered peat, 32°25’01.4”S 19°01’29.9”E (Fig. 1D).
Type material. Holotype (male): “ 28/ix/2024 South Africa WC// Cederberg, Die Vlei along// headwaters of Driehoek River // 32,41670° S 19,12518° E, 943 m // Bilton, Balke et al. leg.” (genitalia extracted and mounted on same card) and red holotype label (AMG).
Paratypes (19): South Africa: 9 ♂, 10 ♀ same data as holotype (AMG, CDTB, CFA, ZSM). All with red paratype labels.
Description. Size: Holotype: TL 2.65 mm; EL 1.85 mm; EW 1.60 mm; EI 1.16. Paratypes: ♂ s BL 2.35–2.55 mm; EL 1.55–1.70 mm; EW 1.45–1.50 mm. ♀ s BL 2.60–2.95 mm; EL 1.75–1.95 mm; EW 1.45–1.65 mm.
Colour: Dorsum (Fig. 1A) with head black, apex of labrum paler, reddish brown; pronotum and elytra dark brown to black, posterolateral angles and lateral margins of pronotum paler, yellowish brown. Maxillary palpi with palpomeres 2–3 dark yellow; palpomere 4 infuscated. Legs reddish brown, distal portions of femora somewhat lighter. Underside of head black. Pronotal and abdominal ventrites dark brown to black; pronotal hypomera and elytral epipleurs reddish brown.
Head: Clypeus large, with bluntly rounded anterolateral angles and distinctly concave anterior margin; lateral margin longer than longitudinal diameter of compound eyes. Clypeus and frons shining, without microreticulation and with shallow, irregular, medium punctures, spaced on average 2–3 puncture-widths apart. Frontoclypeal suture very weak and shallow, not visible on all specimens. Compound eyes moderate, very slightly protruding, emarginate anteriorly; ventral portion smaller than dorsal (approximately ¾ size). Antennae with eight antennomeres. Maxillary palpi moderately slender, half as long as maximum width of clypeus; palpomere 2 distinctly inflated. Palpomeres 2: 3: 4 = 0.08 mm: 0.07 mm: 0.14 mm. Labial palpi moderately slender, elongate, slightly longer than lateral margin of mentum.
Pronotum: Transverse, highly arched, broadest at posterior angles. Anterior and posterior angles broadly rounded; anterior angles slightly protruding. Anterior margin arcuate over central 0.5; posterior margin almost straight over central third, arcuate laterally. All margins with narrow bead. Lateral margins without evident setae. Surface shining, without microreticulation; punctures spaced and sized as on head; somewhat shallower in some specimens, particularly posteriorly and laterally.
Elytra: Oval, broadest behind middle; arcuate over anterior third, then evenly rounded to apex; weakly emarginate around suture. Lateral margins without setae. Humeral region without evident callosity. Sutural stria present on posterior two thirds of elytra. Upper surface shining, without microreticulation. Punctures spaced as on head and pronotum, larger and deeper; distinct series and impressed striae absent.
Venter: Mentum flat with convex lateral margins; distinctly depressed anteriorly, anterior margin slightly emarginated; lateral margins with dense brushes of long, flattened setae. Surface shining, without microreticulation and with sparse setiferous punctures. Prosternum slightly tectiform, without median carina. Mesoventrite flat, without evident process. Abdominal ventrites entirely pubescent; ventrite 5 not emarginate apically.
Legs: Procoxae without spine-like setae. Profemora (Fig. 1B) pubescent on proximal half of ventral face with slightly oblique hairline, broadest approximately one third from anterior margin; mesofemora (Fig. 1B) pubescent on proximal half along anterior margin, obliquely reducing to ¼ of posterior margin; metafemoral pubescence (Fig. 1B) reduced to a narrow strip over mesal half of anterior margin and on proximal portion, adjacent to metatrochanter. Metatibia with strong spines on lateral face; distal spurs slender, longer mesal spur reaching midway along tarsomere 2 (Fig. 1A). Metatarsus slightly shorter than metatibia.
Aedeagus: Phallobase shorter than parameres (Fig. 1C), slightly longer than wide, evenly converging to the distinct, broad knob-like manubrium. Ventral face of phallobase largely unpigmented, borderline between unpigmented and pigmented part of ventral face reaching manubrium. Parameres with undulated mesal margins and straight to weakly arcuate lateral margins, distinctly inflated and angled internally at their apices. Ventral bases of parameres fused. Dorsal bases curved, just reaching into phallobase. Median lobe wide, short, widening from the base to approximately halfway along its length, then almost parallel to approximately 1/5 from apex, then narrowing abruptly to a distinct point. Apex of median lobe not reaching apex of parameres, ending close to start of apical expansion of parameres; corona in apical position. Basal apophyses as long as main piece of median lobe, with distinct extension into phallobase, pointing mesad. Aedeagal length 0.40− 0.45 mm.
Female: Not significantly different from males, other than slightly larger size—see above.
Variation: Some variation in punctation and impression of frontoclypeal suture and size as noted above.
Etymology. Named after Professor Garth Foster, Ayr, Scotland, water beetler extraordinaire and mentor to the first author, on occasion of his 80 th birthday.
Distribution and ecology. A. fosteri sp. nov. is known only from the type series, taken at an altitude of ca. 943 m in a plateau seepage bog (Fig. 1D) surrounded by montane fynbos below Uitkyk Pass in the Cederberg, Western Cape Province, South Africa. Beetles were netted from algal encrusted wet peat amongst grasses, sedges and restios, the saturated substrate having to be stamped down in order to reveal nettable water. DTB has visited this area a number of times since 2009 and every time this algal-covered peat has been damp, but without accessible water. It thus seems highly likely that the species is semi-terrestrial, living much of the time on damp ground out of liquid water. Such a lifestyle is known in other Anacaena in the region including A. endroedyi (Hansen, 1999) and A. striata (Hansen, 1999). A. glabriventris Komarek, 2004, whilst often living in water, can also frequently be found in damp terrestrial litter beside seepages and madicolous habitats in South Africa (DTB, pers. obs.). Elsewhere, some species of the genus frequently occur in similar habitats, including the widespread Palaearctic A. globulus (Paykull, 1798) (e.g. Balfour-Browne 1958). The only other water beetle found in association with A. fosteri sp. nov. was Relictorygmus trevornoahi Seidel, Minoshima, Arriaga-Varela & Fikáček, 2018. This beetle was described from wetlands in the southern Western Cape (Seidel et al. 2018), at low elevation and its discovery in the Cederberg is rather unexpected. Interestingly, the third species of Relictorygmus in South Africa, recently discovered from high-altitude (1167 m) in the Kamiesberg, Northern Cape Province, also co-occurred with an Anacaena species (A. glabriventris) (Bilton & Mlambo 2014) and R. trevornoahi co-occurred with A. capensis Hebauer, 1999 (Seidel et al. 2018). Specimens collected in 2024 closely match an examined paratype of R. trevornoahi externally and on male genitalia.
The area from which the new species was collected forms the source of the Driehoek River, being labelled Die Vlei or Driehoek Vlei on maps and is a major river system draining central Cederberg before joining the Doring River (Quick & Eckardt 2015). It is one of the sites from which pollen cores have been extracted to examine Late Pleistocene to Holocene vegetation changes in the region (Meadows & Sugden 1991), peat deposition here apparently dating to at least 14,600 bp. This area of the high Cederberg supports a number of localised endemics, including water beetles (Bilton 2014) and mesic terrestrial invertebrates such as Onychophora (likely Peripatopsis cederbergiensis Daniels, McDonald & Picker, 2013; DTB pers. obs.). A. fosteri sp. nov. occurs relatively close geographically to A. namaqua Bilton & Komarek, 2016, but in quite a different microhabitat apparently, at higher altitude.
Differential diagnosis. The new species is most similar structurally to A. capensis, A. glabriventris, A. namaqua, A. reducta Komarek, 2004 and A. tenella Hebauer, 1999, sharing the following features with these South African species: eight antennomeres, no preocular patches on clypeus, flat mesoventrite, colouration of the pronotum (dark brown to black with yellow lateral margins), absence of serial elytral punctures and reduced metafemoral pubescence. The new species can be readily separated from A. namaqua by its uniformly dark coloration and the form of the aedeagus. Anacaena fosteri sp. nov. can be distinguished from A. reducta and A. tenella on its generally larger body size (2.35–2.95 vs. <2.5 mm), from A. glabriventris on the entirely pubescent abdominal ventrites and the very different aedeagus and from A. capensis on its distinctly different aedeagus. It is further distinguished from A. capensis and A. glabriventris by the less elongate habitus, the less impressed frontoclypeal suture and the darker dorsal pigmentation, with pale pronotal margins narrower and much less evident. The aedeagus, with the paramere apices greatly surpassing the tip of the median lobe (Fig. 1C) is unique within the known South African fauna.
description: Published as part of Bilton, David T., Mlambo, Musa C. & Balke, Michael, 2025, A new species of Anacaena Thomson, 1859 from the Cederberg Range, South Africa (Coleoptera: Hydrophilidae), pp. 165-170 in Zootaxa 5613 (1) on pages 166-168, DOI: 10.11646/zootaxa.5613.1.8, http://zenodo.org/record/15216327