Decarthrocerus Orchymont, 1948

Perkins, Philip D., 2009, Revisions of the genera Parhydraena Orchymont, Protozantaena Perkins, Decarthrocerus Orchymont, and Parhydraenopsis nomen novum, aquatic and humicolous beetles from Africa and Madagascar, and comparative morphology of the tribe Parhydraenini (Coleoptera: Hydraenidae), Zootaxa 2038, pp. 1-119 : 52-53

Decarthrocerus Orchymont, 1948

Decarthrocerus Orchymont, 1948: 34 (type species Decarthrocerus jeanneli Orchymont , by original designation). Parhydraena (Decarthrocerus) : Perkins, 1997 (morphology).

Parhydraena (Decarthrocerus) : Hansen, 1998 (catalog).

Diagnosis. Distinguished from Protozantaena , Discozantaena ,and Parhydraenopsis by the presence of an hypomeral carina (e.g., Figs. 2, 3, 88), and the markedly different habitus ( Fig. 1). Distinguished from Parhydraena by the markedly different habitus, the wide antennal pocket with differently placed and differently shaped hypomeral pocket setae, the very wide antennal grooves of the head, and the markedly different aedeagal form. Recognized by the moderate size (length ca. 2.17–2.29 mm); the rather flattened, cordiform pronotum; the convex elytra; the prominent, backward arching dorsal setae; the ten-articled antenna (five + club) which is much longer than the maxillary palpi; the hypomeral carina; and the hypomeral antennal pocket setae originating in hydrofuge area (none along the lateral margins of the pocket), elongate, and group together at their tips.

Description. Body size moderate, length ca. 2.17–2.29 mm. Form elongate oval; pronotum transverse, cordiform, markedly attenuate posteriorly, transversely convex; elytra markedly attenuate posteriorly, transversely convex; head wide and short, anterior margin in habitus view evenly arcuate. Entire dorsum with prominent, backward arching setae. Antenna much longer than maxillary palpus, ten articles (five + club), second ovoid, slightly shorter than combined lengths of third to fifth;. Maxillary palpus short, length/head width ratio ca. 0.32–0.43; ratios of articles two to four (last) slightly variable, but fourth always longest and third always shortest (e.g., 5/2/7 and 6/3/9). Eyes small, not elevated, 6–7 facets in longest series in dorsal aspect. Labrum set at marked angle to clypeus, not visible in habitus view, anterior margin weakly emarginate. Clypeus anterior margin and frontoclypeal suture arcuate. Ocelli weakly convex, indistinct in some species, located slightly closer to midline than to eyes. Frons very weakly convex between ocelli; area behind and between ocelli lacking carinae. Pronotum with anterior and posterior transverse impressions on disc, impressions broadly U-shaped; anterior hyaline border present over about median third, extremely narrow. Hypomeron with carina at lateral margin of hydrofuge pubescence; antennal pocket very wide, posteriorly but not laterally with elongate hypomeral antennal pocket setae, numbering ca. 6–7, setae joining together distally. Proventral antennal cleaner, a dense cluster of sharp spines, located on anterolateral margin of each side of proventrite. Metaventrite with impression on disc in basal 1/2, midlongitudinal carina between impression and mesoventral intercoxal process. Elytra with ten rows of large, deep punctures, six between suture and humerus, setae of both series and intervals large, arching posteriorly. Intercoxal sternite small, triangular. Aedeagus with distal piece articulating with main-piece, complicated but small, gonopore at tip of very short process; parameres absent.