Revision of the Neotropical diving beetle genus Hydrodessus J. Balfour-Browne, 1953 (Coleoptera, Dytiscidae, Hydroporinae, Bidessini) Author Miller, Kelly B. text ZooKeys 2016 580 45 124 http://dx.doi.org/10.3897/zookeys.580.8153 journal article http://dx.doi.org/10.3897/zookeys.580.8153 1313-2970-580-45 745750AD4D4241E599B9FDEFDE0C5BED Taxon classification Animalia Coleoptera Dytiscidae Hydrodessus phyllisae Spangler, 1985 Figs 7A, 29, 41, 47 Hydrodessus phyllisae Spangler, 1985: 86; Bistroem 1988 : 37; Nilsson 2001 : 236. Type locality. Guyana, Mazaruni-Potaro District, Takutu Mountains, 6°15'N 59°5'W Diagnosis. This species is part of a group including Hydrodessus maculatus , Hydrodessus latotibialis and Hydrodessus tenuatus that have the lateral elytral carina long (half or more the length of the elytron) (Fig. 29B), the prosternal process broad (length/width <2) (Fig. 29C), and the metaventral platform (the region between the metaventrite carinae) conspicuously constricted near the base of the metaventral process and broadly divergent posteriorly (Fig. 29C). Hydrodessus phyllisae differs from Hydrodessus maculatus in having the elytra red with only indistinct, weakly defined pale regions on the elytron (Fig. 29A), and from Hydrodessus tenuatus in having the pro- and mesotarsi broad with a subapical emargination (Fig. 7A). From Hydrodessus latotibialis , this species differs in size. Hydrodessus phyllisae are smaller (TL <2.7 mm) than Hydrodessus latotibialis (Tl> 2.9 mm). Also, specimens are more matte than Hydrodessus latotibialis which are dorsally shiny. Unfortunately, male specimens of Hydrodessus latotibialis were not available, so the usually definitive male gentalia were not examined for comparison. Description . Measurements. TL = 2.5-2.6 mm, GW = 1.2 mm, PW = 1.0 mm, HW = 0.7 mm, EW = 0.4 mm, TL/GW = 2.1-2.2, HW/EW = 1.7-2.0. Body shape moderately robust, apically rounded, lateral margins distinctly discontinuous between pronotum and elytron (Fig. 29A). Coloration (Fig. 29A). Head orange. Pronotum yellow. Elytron yellow brown with vague pale areas anteriorly, laterally, subapically and at apex. Antennae, palps, and legs yellow. Venter yellow-brown, lighter on prothorax and epipleuron. Sculpture and structure. Head broad, anterior margin subtruncate medially; surface covered with minute punctures; eyes moderately small. Pronotum subcordate, widest near middle (Fig. 29A); lateral bead fine, somewhat obscured anteriorly; surface shiny with fine punctures. Elytra elongate, apically rounded (Fig. 29A); lateral carina distinct near humeral angle, extending as low, indistinct ridge posteriorly to about 1/2 length of elytron (Fig. 29B); surface shiny, covered with fine punctures. Prosternum medially carinate, setose; prosternal process moderately broad, subrectangular but widest at anterior laterally-expanded lobes, lateral margins slightly concave, subparallel, apex shallowly rounded, longitudinally strongly impressed (Fig. 29C). Metaventrite with anterior process moderately large, apically rounded, distinctly subapically constricted; metasternal carinae narrow anteriorly, posteriorly well-marked, strongly and evenly divergent across metasternum, ending near anterior terminus of metacoxal lines (Fig. 29C); other surfaces covered with fine punctures. Legs with most surfaces covered with fine punctures; metatibia with distinctive brush of dense, elongate setae on postero-apical surface; pro- and mesotibiae broad, with broad subapical emargination on dorsal margin; metatrochanter apically rounded but with small, sharp point; metacoxa evenly covered with fine punctures; metacoxal lines well developed, anteriorly slightly divergent but nearly subparallel (Fig. 29C). Abdomen shiny, evenly covered with fine punctures; apex of VI rounded. Male genitalia. Median lobe bilaterally symmetrical, in lateral aspect abruptly and broadly curved, very broad basally, apical portion constricted, slightly expanded along ventral margin, and relatively straight to narrowly pointed apex (Fig. 29D); in ventral aspect moderately broad, lateral margins broadly curved, apex narrowly rounded (Fig. 29E). Lateral lobe broad basally, apical portion somewhat narrowed, evenly constricted to broadly rounded apex, with sparse setae apically (Fig. 29F). Female genitalia. Gonocoxosternite broadly curved, apex narrowly rounded, medially deeply convex, anterior portion large and broad, anteriorly rounded (Fig. 41). gonocoxae with apical portion broad and short, apodemes elongate, slender and apically slightly expanded (Fig. 41). Bursa elongate and broad, membranous; spermathecal duct slender, moderately elongate; receptacle semispherical; spermatheca elongate and curved, not strongly differentiated, without spermathecal spine; fertilization duct short, slender and curved (Fig. 41). Sexual dimorphism. Male pro- and mesotarsi I-III slightly more broadly expanded than female and ventrally with several large adhesive setae; female specimens examined are dorsally more alutaceous. Variation. Specimens vary somewhat in intensity of coloration. Distribution . Hydrodessus phyllisae is known only from the Takutu Mountains of Guyana and Cerro de la Neblina in southern Amazonas, Venezuela (Fig. 47). Habitat. Specimens have been collected from blacklights and several forest habitats including muddy oxbow lakes, pools and leafpacks in whitewater streams, and stream margins. Discussion. Two female specimens from Paraguari, Paraguay (FSCA) resemble Hydrodessus phyllisae in many ways, but not such that they can be convincingly assigned to this species, and they are not included here as part of the concept of the species. Specimens. The holotype male in USNM was examined, it is labeled, "GUYANA: Mazaruni- Potaro District Takutu Mountains 6°15'N , 59°5'W 16 December 1983/ EARTHWATCH Research Expedition: P. J. Spangler & W. E. Steiner Collectors/ At blacklight in forest clearing near streams / HOLOTYPE Hydrodessus phyllisae PJ Spangler [red label]/ BLNO 003805 [blue label with black line around margin]." Other non-type specimens examined, 48 total. Guyana, Mazaruni-Potaro District, Takutu Mountains, 6.25°N , 59.083°W , 12 Dec 1983, R.A. Faitoute (2, KUNHM); same but 18 Dec 1983, berlese of leaf packs from rocky shaded stream, P.J. Spangler, W.E. Steiner, M. Levine (1, KUNHM); same but 17 Dec 1983, at blacklight in forest clearing near stream, P.J. Spangler, W.E. Steiner (2, USNM, including 1 paratype of Hydrodessus phyllisae ). Venezuela, Amazonas, Cerro de la Neblina, 1km S basecamp, 0.833°N , 66.167°W , 19 Feb 1985, along small whitewater stream, pools of dead leaves and sticks, 140m, P.J. Spangler, P.M. Spangler, R. Faitoute, W. Steiner (24, USNM); same but Cerro de la Neblina, basecamp, 0.833°N , 66.167°W , 21 Feb 1985, rainforest clearing near Rio Baria, muddy oxbow pond, 140m, W.E. Steiner (13, USNM); same but Cerro de la Neblina, 1.5km S basecamp, 0.833°N , 66.167°W , 8 Feb 1985, small whitewater stream in rainforest, 250m, W.E. Steiner, R. Halling (1, USNM); same but Cerro de la Neblina, 1km S basecamp, 0.833°N , 66.167°W , 8 Feb 1985, netted along margins of Rio Baria, P.J. Spangler, P.M. Spangler, R. Faitoute, W. Steiner (1, USNM), same but Cerro de la Neblina, basecamp, 0.833°N , 66.167°W , 7 Feb 1985, at blacklight on bank of Rio Baria, 140m, W.E. Steiner (3, USNM).