Radicitus Short & Garcia , 2014

Giron, Jennifer C. & Short, Andrew Edward Z., 2021, The Acidocerinae (Coleoptera, Hydrophilidae): taxonomy, classification, and catalog of species, ZooKeys 1045, pp. 1-236 : 1

Genus Radicitus Short & Garcia, 2014 Figs 1K , 2 , 6 , 49G-L , 50

Radicitus Short & García, 2014: 252.

Gender.

Masculine.

Type species.

Radicitus ayacucho Short & García, 2014: 252; by original designation.

Diagnosis.

Medium sized beetles, body length 4.5-6.2 mm. Body shape oval in dorsal view; moderate to strongly convex in lateral view; dorsal outline nearly straight and anteriorly inclined along anterior half (Fig. 50 ). Color dark brown, usually uniform along body regions, sometimes margins of pronotum and elytra slightly paler; ground punctation fine, moderately marked (Fig. 50A, D ). Shape of head trapezoid and rather wide. Eyes moderate in size, not emarginated anteriorly, slightly projected from outline of head. Clypeus trapezoid, with anterior margin broadly, roundly, and weakly emarginate. Labrum fully exposed. Mentum medially rather broadly depressed, laterally longitudinally elevated; median anterior depression marked by transverse nearly straight carina (Fig. 50C, F ). Antennae with nine antennomeres; cupule slightly asymmetric, with rounded outline. Maxillary palps short and stout, nearly as long as half width of head (e.g., Fig. 50C ); inner margin of maxillary palpomere 2 nearly straight, outer margin strongly curved along apical 2/3; maxillary palpomere 4 slightly shorter than 3. Prosternum flat, only slightly carinate along midline of anterior projection. Elytra without sutural striae; elytral punctures shallow to moderately marked; ground punctures rather uniformly distributed; some species with serial punctures clearly visible along posterior third of elytra; outer margins of elytra slightly flared (Fig. 50A, D ). Posterior elevation of mesoventrite with median longitudinal carina elevated and forming posteriorly pointing process; anapleural sutures strongly concave, separated at anterior margin by distance nearly half width of anterior margin of mesepisternum. Metaventrite sometimes with posteromesal glabrous patch. Protibiae with anterior row of spines completely reduced; apical spurs of protibiae stout, reaching apex of protarsomere 3. Metafemora with tibial grooves very sharply marked and covered by hydrofuge pubescence; hydrofuge pubescence restricted to dorsal half on basal three-quarters of anterior surface of metafemora (Fig. 50C, F ). Tarsomeres 1-4 with long spiniform setae on ventral face; metatarsomere 2 nearly as long as 5 and as 3 and 4 combined. Fifth abdominal ventrite evenly rounded, without apical emargination or fringe of stout setae. Aedeagus either trilobed (Fig. 49I-L ) or divided (Fig. 49G, H ), with basal piece short and rather simple parameres separated from each other for most of their lengths; gonopore well developed.

Differential diagnosis.

Radicitus may resemble some punctate Novochares but can be recognized by the short and stout maxillary palps, along with metafemora only partly covered by pubescence (long and slender maxillary palps with metafemora mostly covered by pubescence in Novochares ).

Distribution.

Neotropical: Guyana, Suriname, Venezuela; Fig. 6 .

Natural history.

Species of Radicitus have been found on a variety of habitats associated with streams and seeps on rock outcrops. Some have been collected by submerging root mats found along streams, and in the roots of vegetation growing on seepage areas on granite outcrops ( Short and García 2014).

Larvae.

The immature stages of Radicitus remain unknown.

Taxonomic history.

Radicitus was only recently described.

Remarks.

There are three known species of Radicitus , all currently endemic to the Guiana Shield.

Selected references.

Short and García 2014: original description of the genus and all known species; Short et al. 2021: phylogenetic placement.

Figures

Figure 1. Variation across Acidocerinae, dorsal and lateral views A Colossochares ellipticus B Peltochares sp. C Peltochares conspicuus D Aulonochares tubulus E Helochares sp. F Helochares tristis G Novochares sp. H Helopeltarium ferrugineum I Batochares sp. J Helobata larvalis K Radicitus sp. L Nanosaphes tricolor M Agraphydrus cf. attenuatus N Tobochares luteomargo O Tobochares sulcatus P Quadriops similaris Q Crucisternum ouboteri R Primocerus neutrum S Agraphydrus coomani T Agraphydrus sp. U Globulosis flavus V Crephelochares nitescens.

Figure 2. Phylogeny of the Acidocerinae simplified from Short et al. (2021), indicating the distribution, preferred habitat, and currently described number of species for each genus. For habitat, filled black circles indicate that at least some species of the genus are commonly found in this habitat; light grey circles indicate the genus has been found in this habitat, but is rare or not typical for the group; white circles indicate no species have been recorded for the genus in this habitat.

Figure 6. Known distribution of genera of Acidocerinae: Novochares, Peltochares, Primocerus, Quadriops, Radicitus, Sindolus, Tobochares, and Troglochares.

Figure 49. Aedeagi of Quadriops, Radicitus and Sindolus spp. A Q. clusia B Q. depressus C Q. reticulatus D Q. similaris E S. sp. (Venezuela) F. S. sp. (Venezuela) G, H R. ayacucho: G dorsal view H lateral view I, J R. cf. granitum (Suriname): I dorsal view J lateral view K, L R. surinamensis: K dorsal view L lateral view. Scale bars: 0.1 mm (A-D); 0.5 mm (E-L).

Figure 50. Habitus of Radicitus spp. A-C R. ayacucho: A dorsal habitus B lateral habitus C ventral habitus D-F R. granitum: D dorsal habitus E lateral habitus F ventral habitus. Scale bars: 1 mm.