Rhithrops, Bilton & Shepard, 2022

Bilton, David T. & Shepard, William D., 2022, Rhithrops capensis gen. et sp. nov., a new aquatic dryopid beetle from the Western Cape of South Africa (Coleoptera: Dryopoidea: Dryopidae), Zootaxa 5195 (6), pp. 539-553 : 540

Rhithrops gen. nov.

( Figs 1–11 )

Type species. Rhithrops capensis sp. nov., by monotypy.

Diagnosis. Rhithrops is unique amongst aquatic dryopid genera in that the labrum is transversely upturned apically. In South Africa, Rhithrops can be separated from Ahaggaria and Dryops by the lack of long erect setae on the eyes and dorsum of the body. Rhithrops can be separated from Strina and Rapnus by the antennae having 10 antennomeres as opposed to nine in Strina and seven in Rapnus . Additionally, Rhithrops has shallow sublateral pronotal furrows rather than sublateral step-like carinae, with discrete gibbosities on the pronotum outside of the sublateral furrows. The dorsally serrate coxites of the ovipositor are only shared with Strina , another South African dryopid genus. Abdominal ventrite 5 lacking a plastron is a character state commonly seen in the genus Helichus Erichson, 1847 .

Figures

FIG. 1. Rhithrops capensis gen. et sp. nov., Holotype habitus. Scale bar = 1 mm.

FIG. 2. South African endemic dryopid genera, dorsolateral view of pronotal margins. A) Rhithrops capensis gen. et sp. nov., holotype male; B) Rhithrops capensis gen. et sp. nov., paratype female; C) Rapnus sp., female; D) Strina sp., female. C) & D) South Africa, Western Cape, Franschoek, Mont Rochelle. Scale bar = 0.5 mm.

FIG. 3. Rhithrops capensis gen. et sp. nov. A) head, posterolateral view; B) compound eye – arrow indicates inter-ommatidial seta; C) detail of dorsolateral sculpture of head, inside compound eye; D) antennae; E) antennomeres 1–2; F) antennomeres 3–10.

FIG. 4. Rhithrops capensis gen. et sp. nov. A) labrum, dorsal view; B) right mandible, ventral view; C) right maxilla, dorsal view; D) close-up of maxillary palp apex; E) female labrum and mentum, ventral view; F) male labrum and mentum, anteroventral view.

FIG. 5. Rhithrops capensis gen. et sp. nov. A) right mandible, ventrolateral view – teeth numbered as in text; B) left mandible, ventral view – pt = prostheca, Lf = lateral flange. Scale bar = 100 μm.

FIG. 6. Rhithrops capensis gen. et sp. nov. A) prothorax, dorsal view; B) close-up of sculpture of pronotal disc; C) Meso and metanotum, with scutellum; D) right elytron, dorsolateral view; E) detail of right elytral apex; F) prothorax, ventral view.

FIG. 7. Rhithrops capensis gen. et sp. nov. A) meso and metaventrites, ventral view; B) male abdomen, ventral view; C) female abdomen, ventral view; D) close-up of plastron vestiture at junction of abdominal ventrites 2–3; E) male abdominal apex; F) female abdominal apex.

FIG. 8. Rhithrops capensis gen. et sp. nov. A) male foreleg, ventral view; B) male foretarsus and tibial apex, ventral view; C) male hind tibia and tarsus, ventral view; D) aedeagus, ventral view; E) aedeagus, lateral view; F) aedeagal apex, ventral view.

FIG. 9. Rhithrops capensis gen. et sp. nov. A) aedeagus, ventrolateral view; B) aedeagus, lateral view; C) male sternite 9; D) aedeagal apex, ventral view (not to scale); E) male tergite 8; F) male sternite 8. Scale bars = 0.5 mm.

FIG. 10. Rhithrops capensis gen. et sp. nov. A) ovipositor, lateral view; B) ovipositor apex, lateral view (not to scale); C) female sternite 8. Scale bar (A & C) = 0.5 mm.

FIG. 11. Rhithrops capensis gen. et sp. nov. Type locality, South Africa, Western Cape, Cederberg, Matjies Rivier, Matjiesrivier, 32°31’07.42”S 19°21’00.4”E, 725 m. Photo D T Bilton.