Hydrodessus morsus, Miller, Kelly B., 2016

Miller, Kelly B., 2016, Revision of the Neotropical diving beetle genus Hydrodessus J. Balfour-Browne, 1953 (Coleoptera, Dytiscidae, Hydroporinae, Bidessini), ZooKeys 580, pp. 45-124 : 91-93

Taxon classification Animalia Coleoptera Dytiscidae

Hydrodessus morsus sp. n. Figs 25, 50

Type locality.

Venezuela, Amazonas, Cerro de la Neblina, basecamp, 0.833°N, 66.167°W.

Diagnosis.

This is the smallest Hydrodessus (TL <1.5 mm). In addition, this species differs in having a low and rounded lateral elytral carina (Fig. 25B), a relatively narrow and apically pointed prosternal process (Fig. 25C), and the metaventrite carinae poorly developed (Fig. 25C). Specimens are concolorous yellow and parallel-sided (Fig. 25A). The male median lobe in lateral aspect is moderately broad basally, weakly curved and apically pointed (Fig. 25D). In ventral aspect the median lobe is slightly constricted subapically and apically rounded (Fig. 25E). The lateral lobe is broad basally and with margins apically evenly convergent to rounded apex (Fig. 25F).

Description.

Measurements. TL = 1.4-1.6 mm, GW = 0.5-0.6 mm, PW = 0.5-0.6 mm, HW = 0.4-0.5 mm, EW = 0.3 mm, TL/GW = 2.4-2.6, HW/EW = 1.6-1.7. Body elongate, parallel–sided, lateral margin distinctly discontinuous between pronotum and elytron, dorsoventrally somewhat compressed (Fig. 25A).

Coloration (Fig. 25A). Body surfaces yellow throughout.

Sculpture and structure. Head elongate, anterior clypeal margin broadly rounded; surface finely punctate and shiny; eyes moderately large and large-faceted. Pronotum cordate, widest anterior to middle (Fig. 25A); lateral bead very fine; surface shiny with fine punctation. Elytra elongate, lateral margins subparallel (Fig. 25A); lateral carina indistinct, rounded, present only at humeral angle (Fig. 25B); surface covered with fine punctures. Prosternum relatively flat, not medially carinate; prosternal process elongate triangular, lateral carinae convergent to narrowly pointed apex, apically narrowly separated from Metaventrite (Fig. 25C). Metaventrite with anterior process narrowly triangular, metasternal carinae represented by low, rounded margin of medial flattened surface extending posteriorly to anterior ends of metacoxal lines (Fig. 25C); surface covered with fine punctation. Legs with surfaces largely shiny and impunctate; pro- and mesotibiae moderately broad; metatrochanter strongly offset and apically rounded; metatibia with posteroapical brush of setae; metacoxa covered with fine punctation; metacoxal lines indistinct, medially somewhat approximated, anteriorly divergent (Fig. 25C). Abdominal ventrites covered with fine punctation; VI apically broadly rounded.

Male genitalia. Median lobe bilaterally symmetrical, in lateral aspect broadly curved, with very broad basal portion, with medial expansion along ventral margin, apically with dorsal margin nearly stright, dorsal margin broadly curved to pointed apex (Fig. 25D); in ventral aspect broad, lateral margins slightly expanded medially, apically with margins slightly convergent to broadly rounded apex (Fig. 25E). Lateral lobe very broad basally, medially curved, apex broad with lateral margins straight and convergent to broadly rounded apex which has small cluster of marginal setae (Fig. 25F).

Female genitalia. Not examined.

Sexual dimorphism. Male pro- and mesotarsi I–III more broadly expanded than female and ventrally with several large adhesive setae.

Variation. Very little variation was observed among the few specimens examined.

Etymology.

This species is named morsus, Latin for "little bit," for the small size of specimens.

Distribution.

This species is found only in Amazonas, Venezuela (Fig. 50).

Habitat.

Nearly all the known specimens were collected at black light.

Discussion.

This extremely small Hydrodessus has only weakly developed lateral elytral carina and metaventrite carinae. The prosternal process is also relatively narrow. Together, these make this species only poorly placed in Hydrodessus , but the male lateral lobes have a single segment, and the overall body shape is consistent with the variation present in the genus. Even so, it is certainly possible this species does not belong in Hydrodessus .

Specimens.

The holotype male is in MIZA labeled, "VENEZUELA,T.F.Amaz. Cerro de la Neblina Basecamp. 140 m. 0°50'N, 66°10'W 7 February 1985/ At black light on bank of Rio Baria W. E. Steiner, collector/ HOLOTYPE Hydrodessus morsus Miller, 2016 [red line with black line border]."

Paratypes, 5 total. Venezuela, Amazonas, Cerro de la Neblina, basecamp, 0.833°N, 66.167°W, 7 Feb 1985, black light on bank of Rio Baria, 140m, W.E. Steiner (4, MIZA, USNM); Amazonas, San Fernando de Atabapo, El Pozo, 4.024°N, 67.684°W, 8 Apr 1988, M. Aleman (1, USNM).