Decarthrocerus mahalicus, Perkins, 2009

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 : 57-58

Decarthrocerus mahalicus new species

( Figs. 89, 91, 103)

Type material. Holotype (male): Tanzania: Tanganyika Terr., Mahali Peninsula , Kungure, south ridge, leaf litter and detritus in small gully in dense wet forest, elev. 1829 m, 6° 10' S, 29° 50' E, 15.xi.1959. Deposited in the BMNH . Paratype: Same data as holotype (1 MCZ) .

Differential diagnosis. Recognized by the comparatively wide pronotum and short elytra (pronotal width/elytral length ratio ca. 0.71) ( Fig. 89). The aedeagus is very distinctive ( Fig. 91).

Description. Size (length/width, mm) holotype: body (length to elytral apices) 2.20/1.00; head 0.34/0.64; pronotum 0.55/0.92, PA 0.74, PB 0.64; elytra 1.30/1.00. Color brown to dark brown, lateral areas of pronotum lighter than disc; maxillary palpi light brown; dorsum with stiff, arcuate, yellow setae (dorsum usually thickly coated with debris).

Head with eyes small in dorsal aspect, ca. 7 convex facets in longest series. Ocelli distinct, margined with groove laterally, interocular foveae very small, narrow. Frons markedly concave laterally, hence eyes appearing elevated; occipital area with strong carina on each side of midline, longitudinal depression between carinae continued as shallow impression on posterior of frons disc; cuticle dull, with granule at base of each arcuate seta, granules ca. 1xef or smaller. Frontoclypeal suture widely U-shaped. Clypeus with setae and granules like frons. Labrum dull, set at angle to clypeus, hidden in habitus view, apicomedially weakly emarginate. Maxillary palpi very short, combined lengths of meres much less than width of head (ratio ca. 15/ 41); ratios of meres 2–4 ca. 5/2/8. Mentum and submentum finely, moderately sparsely punctulate, moderately setose, interstices shining.

Pronotum with anterior margin straight, median 2/5 with narrow hyaline border. Anterior angles obtuse, rather sharply rounded. Sides coarsely denticulate or crenulate, rounded, widest at about midlength, behind markedly attenuate, emarginate. Posterior angle obtusangulate. Discal relief prominent, weakly shining, partially divided into two lobes by shallow posterior extension of anterior impression; granules round, ca. 1xef, separated by ca. 2–3xef. Anterior and posterior impressions deep, anterior extended posteriorly in midline, laterally anterior impression continuous with deep impression at each anterior angle; deep, wide impression at each posterior angle; distinct round impression between impressions at angles, area lateral to round impression appearing slightly inflated; granules in impressions longitudinally elongate. Sculpture laterally sparsely granulate, weakly shining.

Elytra moderately shining, sides arcuate, markedly attenuate posteriorly; margins distinct from shoulder for ca. 4/7 of length. Ten-seriate punctate, punctures deep and large, on disc ca. 5xef or larger, separated by less than puncture diameter; each puncture with decumbent seta about as long as, but much less erect than interval setae, no granule at base. Intervals shining, width ca. 1xpd, each with unilinear row of rather widely spaced, large, stiff, arcuate setae, most slightly larger than setae of pronotum.

Metaventrite with moderately deep median elongate oval impression in basal 2/3, strong midlongitudinal carina between anterior extreme of oval impression and mesoventral intercoxal process. Metaventrite and abdominal ventrites 1–4 hydrofuge pubescent. Apical ventrites elongate. Ventrite 5 hydrofuge pubescent in basal 1/4, shining part pubescent in band across posterior 1/2; ventrite 6 simple, with band of setae across posterior 1/2; last ventrite symmetrical, apex very sharply rounded. Female unknown.

Legs moderately short, femora stout, tarsi very short, claws very small, combined lengths of metatibia and metatarsus about equal to width of head (ratio ca. 41/41), ratio of lengths of metatibia/metatarsus ca. 30/11. Basal 3 tarsomeres markedly setose.

Wings apparently fully developed, in folded condition attaining posterior 3/4 of elytral length.

Aedeagus length ca. 0.40 mm; main-piece wider in ventral than in lateral view; in ventral view very slightly sinuate and bearing small cluster of long setae near midlength, apex with minute hook; in lateral view main-piece angulate near midlength, distal 1/2 narrower than basal 1/2; distal piece comparatively small ( Fig. 91).

Etymology. Named in reference to the known geographical distribution, the Mahali Peninsula.

Distribution. Currently known only from the type locality on the Mahali Peninsula in Tanzania ( Fig.

103).