The following description is reproduced with some modifications from Miller et al. (2024).

Nilssondytes diversus sp. nov., by current designation.

From other Cybistrinae this genus differs in having: (1) the metatibial spurs apically simple, (2) metacoxal lines clearly present, (3) the pronotum and elytron with broad, distinct lateral yellow bands along margins (Fig. 1), (4) males and females each with two metatarsal claws, the posterior much reduced in both sexes (Figs 2, 3), (5) the prosternum and prosternal process relatively shallowly but distinctly sulcate (Fig. 4), (6) the medial margins of the male sternite IX straight, not emarginate (Fig. 10), (7) no cluster or line of setae at the apicodorsal angle of the posterior surface of the mesotarsomeres (Fig. 5), and (8) the ventral surface of the metatrochanter with an oblique, transverse groove. The single species in this genus (described below) is somewhat similar in size, shape, and coloration to Metaxydytes laevigatus (Olivier) and may be present among series of that species in collections. Nilssondytes differ from M. laevigatus in several features (see above) including the presence of yellow lateral elytral margins (Fig. 1) which are absent in M. laevigatus. Larvae are unknown.

This genus is named Nilssondytes from the Greek dytes meaning “diver,” and Nilsson, after the great diving-beetle worker and excellent friend, Anders N. Nilsson, in honor of his inestimable contribution to the science of diving-beetle biology.

The single species of Nilssondytes gen. nov. is part of the clade that includes species with an oblique metatrochanteric groove, but it has an unresolved position with respect to other genera (Miller et al. 2024). The presence of a reduced posterior metatarsal claw in both males and females (Figs 2, 3) with straight medial margins of the male abdominal sternite IX (Fig. 10) is a unique combination of features within Cybistrinae. Unique among this larger clade is also the sulcate prosternum and prosternal process (Fig. 4) which is somewhat similar to the Australian genera Spencerhydrus Sharp, 1882 and Sternhydrus Brinck, 1945.

The following description is reproduced with some modifications from Miller et al. (2024).

Venezuela, Amazonas State, roadside pond ca. 7 km S Samariapo 5°10.900'N, 67°46.078'W, 95 m elev.

This is the only species in the genus and is characterized by its diagnostic combination (see above). Typically, species-level features include the shape of the male median lobe which is unique. In ventral aspect the apex is abruptly constricted with the apex narrowly truncate with laterally pointed processes (Fig. 6). In lateral aspect, the median lobe is moderately evenly curved on the dorsal margin, apically abruptly narrowed with the apex elongate and slender, apex narrowly rounded (Fig. 7).

Measurements. TL = 16.7–19.4 mm, GW = 9.6–10.7 mm, PW = 7.0–8.1 mm, HW = 4.2–4.7 mm, EW = 2.7–2.9 mm, TL/GW = 1.7–1.8, HW/EW = 1.6–1.7, WC/WV = 3.1–3.2. Body shape suboval, slightly expanded posteriorly, widest at ~ 3/5 of length (Fig. 1); lateral margins evenly, continuously curved between pronotum and elytron. Depressed and somewhat flattened in lateral aspect.

Coloration (Fig. 1). Head dark green, anterior clypeal margin yellow, more so laterally, testaceous near eyes. Pronotum dark green with broad lateral yellow margin, posteriorly interrupted and green in three of the four examined specimens, in other specimen yellow extending to posterior angle. Elytron dark green with broad lateral yellow band, separated narrowly from lateral margin, slightly expanded near apex. Ventral surfaces largely black, testaceous on head, basal leg segments and elytral epipleuron.

Sculpture and structure. Head broad, frontoclypeal lines elongate, straight, strongly oblique; anterior clypeal margin broadly, shallowly and evenly concave; dorsal surface evenly covered with fine microsculpture and micropunctures. Pronotum with lateral margins evenly and broadly curved; surface similar to surface of head in microsculpture and micropunctation. Elytral lateral margin evenly and slightly curved for most of length, apically broadly curved; surface of elytron similar to surface of head in microsculpture and micropunctation. Prosternal process apically rounded, ventral surface distinctly sulcate (Fig. 4), apex robust, acutely pointed. Metaventral wing broad, slightly less than 1/3 width of lateral portion of metacoxa (WC/WV = 3.1–3.2); surface smooth, without sculpturing. Lateral portion of metacoxa large, broad, surface smooth, without sculpturing; metacoxal lines short, extending less than half distance across metacoxa. Abdominal ventrites smooth, unsculptured.

Male genitalia. Male median lobe in ventral aspect broad throughout most of length, apically abruptly narrowed, apex laterally produced, submedially with broad, elongate lobes on each side, ventral sclerite short, apically sharp, acuminate, extending to 3/5 length of median lobe, apex sharply pointed (Fig. 6). In lateral aspect shallowly curved, apically abruptly narrowed, apex narrowed, slightly curved, apically narrowly rounded, broad medially (Fig. 7). Lateral lobe broad in basal half, apically distinctly narrowed, apex narrowly rounded, with series of elongate setae along more than apical half of dorsal margin of lateral lobe (Fig. 8).

Figures 1–10. 

Nilssondytes diversus sp. nov. 1 dorsal habitus 2, 3 metatarsal claws, posterior aspect: 2 male 3 female 4 prosternal process, ventral aspect 5 right mesothoracic leg, posterior aspect 6–8 male genitalia: 6 median lobe, ventral aspect 7 median lobe, right lateral aspect 8 right lateral lobe, right lateral aspect 9 female genitalia (gonocoxae, laterotergites, right gonocoxosternite and internal genitalia), ventral aspect 10 male sternite IX, ventral aspect. Scale bars: 5.0 mm (1); 1.0 mm (2–5, 9, 10)

Figure 11. 

Distribution of Nilssondytes diversus sp. nov. in northern South America.

Female genitalia. With a single genital opening, vagina elongate, slender, with enlarged, bulbous region at base of common oviduct; spermatheca short, curved, at apex of enlarged region, with soft tissue region on each side of enlarged region (Fig. 9); gonocoxae together broad, apically broadly pointed (Fig. 9); gonocoxosternite broad, with elongate anterolateral lobe, with medial margin sublinear, without conspicuous setae (Fig. 9).

Sexual dimorphism. Males have a characteristic broad protarsal palette with ventral adhesive setae. Males also have mesotarsomeres with clumps of posteroventral setae. Females lack pro- and mesotarsal expansions or adhesive setae. Both males and females have two metatarsal claws with the posterior shorter than the anterior (Figs 2, 3), but females have the posterior somewhat more curved than in males (Fig. 3). Females have distinctive microsculpture on the surface of the elytron anteriorly in the form of a field of short striae which is absent in males.

Variation. Five specimens were examined. One specimen has the lateral pronotal yellow band extending to the posterior margin of the pronotum, the others have a narrow dark green separation from the posterior margin.

This species is known from few localities in Venezuela along the northwestern margins of the Guiana Shield craton (Fig. 11).

The only natural history information available from labels is “roadside pond,” “river margin,” and “rock outcropping.”

The species is named from the Latin diversus, meaning “different,” in recognition of the different lengths of the metatarsal claws in both males and females (Figs 3, 4).

Holotype , male deposited in MIZA (see above) labeled, “Venezuela: Amazonas State 5°10.900'N, 67°46.078'W, 95 m ca. 7 km S. Samariapo 15.i.2009; leg. Short, Miller, García, Camacho, Joly VZ09-0115-02X: roadside pond/ SM0846115 KUNHM-ENT [barcode label]/ Holotype: Nilssondytes diversus Miller, Michat & Ferreira-Jr., 2024 [red label with double black line border].” Paratypes, 1 male (SEMC) labeled, “Suapure Venez. Caura River 4.20.1900 [handwritten] E.A. Klages.”, 1 female (MIZA) labeled “Venezuela: Bolivar State 7°41'23.6"N, 64°1'56.0"W, 134 m ca. 14 km E Rio Aro; 5.viii.2008 leg. A. Short $ M. García AS-08-073; rock outcropping/ SM0829328 KUNMH-ENT [barcode label],” 1 female (SEMC) labeled “Venezuela: Guárico State 8°6.226'N, 66°26.228'W, 52m UCV San Nicolasito Field Station: Rio Aguaro; 10.i.2009 leg. Short, Miller, Joly, García, Camacho; VZ09-0110-01A/ SEMC0852602 KUNHM-ENT,” 1 male (MSBA) labeled “Venezuela: Bolivar State 6.58694°N, 67.02912°W Rio Caripito 12.i.2009; leg. Short Miller VZ09-0112-02A: river margin/ SM0844405 KUNHM-ENT [barcode label].” All paratypes with, “…Paratype Nilssondytes diversus Miller, Michat and Ferreira-Jr., 2024 [blue label with black line border].