Gyrinus (Oreogyrinus) iridinus, Gustafson & Short, 2017

Gustafson, Grey T. & Short, Andrew E. Z., 2017, Review of the whirligig beetle genus Gyrinus of Venezuela (Coleoptera: Gyrinidae), Acta Entomologica Musei Nationalis Pragae 57 (2), pp. 479-520 : 502-505

Gyrinus (Oreogyrinus) iridinus sp. nov.

( Figs 37–38 , 50 , 57 , 74 )

Type material. HOLOTYPE: J, ‘ VENEZUELA, Amazonas / stream nr. Summitof / Unturan Range, CL 8012 / II Feb. 1989 D. A. Polhemus’ ( USNM) . PARATYPES (20 spec.): same as holotype ( USNM, SEMC, MIZA).

Diagnosis. Body form ( Fig. 37 ) oval, in lateral view strongly convex; pronotal disc with transverse crease weakly impressed, without wrinkles laterally; dorsal surface strongly iridescent; elytral disc of female and male similar, all intervals non-reticulate, striae I–IV with small weakly impressed punctures, punctures of V–XI larger and more well impressed, striae VIII–X weakly sulcate; elytral lateral margin narrow, without riffles, not interrupted before apex; elytra apex truncate; metanepisternal ostiole present; aedeagus ( Fig. 50 ) with median lobe just broaderin width than single paramere, weaklyconstricted inapical 1/3, apex broadly rounded; parameres rounded apically; gonocoxae ( Fig. 57 ) curved, with rounded apices.

Description. Size. Female length = 4.0– 4.5 mm, width = 2.5–2.7 mm; male length = 3.5–4.0 mm, width = 2.5 mm. Habitus. Body form evenly oval, attenuated anteriorly and posteriorly, widest point justposteriad of humeral region; in lateral view dorsoventrally strongly convex, greatest convexity posterior to scutellar region, evenly depressed anteriorly and posteriorly.

Coloration ( Fig. 37 ). Dorsally, head, pronotum, elytra black, with strongly iridescent reflections. Venter overall darkly colored; mouthparts, ventral surface of antennal pedicel, prosternum laterally, propleuron, hypomeron, elytral epipleuron, mesocoxal apex, metacoxal apex, posterior half of abdominal sternite VII, and ultimate abdominal ventrite lighter in color – reddish brown to darker orange yellow; legs yellow in color; remainder of venter dark brown to black.

Sculpture and structure. Pronotum of both sexeswith broad nearly unriffled lateral margins, only very few weak riffles anteriorly; pronotal disc with weakly impressed transverse crease, without considerable wrinkles laterally, onlywrinkled medially near posterior margin. Female and male elytra similar ( Figs 37–38 ), striae I–IV with very small, weakly impressed punctures; striae V–XI with larger more well impressed punctures; striae VIII–X weakly sulcate in anterior half; stria XI mostly marginal, briefly raised after basal 1/4 of elytral length. Elytral intervals of both sexes completely without reticulation. Elytra lateral margins narrow, completely unwrinkled, slight sub-apical swelling noticeable, not distinctly interrupting margin; elytral apex truncate. Metanepisternal ostiole small.

Male genitalia ( Fig. 50 ). Aedeaguswith median lobe about as long as parameres, width just wider than widthof singleparamere, attenuated inbasal 2/3, weakly constricted before apical 1/3, apical 1/3 with lateral margins rounded, apex broadly rounded; in lateral view dorsally curved; parameres with rounded apex. Female genitalia ( Fig. 57 ). Gonocoxae curved, apices rounded, left gonocoxa somewhat less curved than right.

Variability. There was someminorvariation inhow sulcateelytralstriae VIII and IX appeared, less so in X, as this was the most shallow of the sulcate striae (bearing in mind striae VIII–X of G. iridinus sp. nov. are all weakly sulcate when compared to other Oreogyrinus species). Differential diagnosis. Gyrinus iridinus sp. nov. is most similar to G. (Oreogyrinus) opalinus Régimbart, 1883 ( Fig. 81 ), being strongly iridescent, small in size (less than 6.0 mm), and having truncate elytral apices, which distinguishes both species from G. (Oreogyrinus) fittkaui Ochs, 1963 . Gyrinus iridinus sp. nov. differs from G. opalinus by having a narrow lateral margin of the elytra, completely lacking any riffles, which is not interrupted by a subapical swelling ( Fig. 37 ); and by having elytral intervals VIII–X weakly sulcate. Gyrinus opalinus has a broad elytral lateral margin ( Fig. 81 ), possessing minute riffles ( OCHS 1954), that is distinctly interrupted by a subapical swelling ( Fig. 81 ), and more strongly sulcate lateral elytral intervals. Gyrinus iridinus sp. nov. also has the pronotal lateralmargins nearly unriffled, compared to that of G. opalinus which is considerably riffled ( Fig. 81 ). Based on the description provided by OCHS (1954) the aedeagus of G. opalinus differs from that of G. iridinus sp. nov. by being narrower, ca. the width of a paramere, and having the anterior half subparallel, compared to G. iridinus sp. nov. which has a broader median lobe, which is just wider than the width of a paramere, constricted before its apical 1/3, with the apical 1/3 possessing rounded lateral margins ( Fig. 50 ).

Etymology. The specific epithet iridinus refers to the new species’ rainbow iridescence, and is selected for its similarity to the name G. opalinus , the species G. iridinus appears most similar to. It is treated as a noun in apposition.

Habitat. The label data indicates the specimens came from a stream near the summit of the Unturán mountain range.

Distribution. Known only from the type locality in the Unturán Mountains of far southern Amazonian Venezuela ( Fig. 74 ).

Discussion. This species lacks nearly all the morphological characters of an Oreogyrinus . The pronotum isvery weaklysculptured ( Figs 37–38 ), withthe transverse creasefaintly impressed, and lacking the strong wrinkles present inother Oreogyrinus species ( Figs 39–40 ). The lateral margins of the elytraare narrow, unriffled ( Figs 37–38 ), andare not terminated in a plica. The pronotal lateral margin, while broad, is also almost completely without riffles, save for a few faintly evident anteriorly. The lateral striae are not well impressed and sulcate in appearance. Elytral stria XI is not strictly marginal, instead it is briefly elevated in the basal half of the elytra, similar to members of the nominotypical subgenus. The male and female are also not strongly sexually dimorphic ( Figs 37–38 ), unlike the majority of other Oreogyrinus species ( Figs 33–36 ). The ventral coloration is similar to an Oreogyrinus , however, this coloration is not unique to Oreogyrinus species, being present in other Nearctic nominotypical species like G. affinis Aubé, 1838 . The only morphological charactertosuggest this species isa memberof Oreogyrinus is the faintly evident riffles inthe anteriorportion of the pronotal lateral margins. The primary reason this species is being classified here as an Oreogyrinus , is because it is a South American species lacking the features uniting members of Neogyrinus (see discussion above on the Gyrinus subgenera), and as currently defined the nominotypical subgenus is absent from South America ( OCHS 1954). Interestingly, the species most similar to G. iridinus sp. nov. is G. opalinus ( Fig. 81 ), a rarely collected species, known from the Atlantic forest of Brazil, with the only specific localities available being, Nova Friburgo, Rio de Janerio, and Lago de Jequiá, Jequiá da Praia, Alagoas, Brazil ( OCHS 1954: 132).

Figures

Figs 33–38.Dorsal habitus of Oreogyrinus species, scale bar = 1 mm. 33 – Gyrinus venezolensis Ochs, 1953, female. 34 – G. venezolensis, male. 35 – G. vinolentus sp. nov. female. 36 – G. vinolentus, male. 37 – G. iridinus sp. nov., female paratype. 38 – G. iridinus, male holotype.

Figs 47–50. Dorsal and lateral view of the aedeagus of Oreogyrinus species, not to scale. 47 – Gyrinus colombicus Régimbart, 1883, syntype (MNHN). 48 – G. venezolensis Ochs, 1953. 49 – G. vinolentus sp. nov. 50 – G. iridinus sp. nov.

Figs 51–59. Ventral view of gonocoxae of Venezuelan Gyrinus species, not to scale. 51–56 – Neogyrinus species. 51 – G. gibbus Aubé, 1838 from Caracas valley, Venezuela (FMNH). 52 – G. gibbus from Amazonian Venezuela: Amazonas stream along Rio Sipapo (KBMC). 53 – G. ovatus Aubé, 1838 from Venezuela: Falcón: W. Curimagua, Blackwater Lagoon.54 – G. guianus Ochs, 1935 from Amazonian Venezuela:Amazonas:river near Orinoco /Sipapo confluence (KBMC). 55 – G. rozei Ochs, 1953. 56 – G. sabanensis sp. nov. 57–59 – Oreogyrinus species: 57 – G. iridinus sp. nov. 58 – G. venezolensis Ochs, 1953. 59 – G. vinolentus sp. nov.

Figs 72–75. Distribution maps of Gyrinus species within Venezuela.

Figs 76–81. Type specimens and associated labels. 76 – Gyrinus amazonicus Ochs, 1958, paratype male (BMNH). 77 – G. guianus Ochs, 1935, holotype female (BMNH). 78 – G. racenisi Ochs, 1953, paratype female (SMF). 79 – G. rozei Ochs, 1953, paratype male (SMF). 80 – G. venezolensis Ochs, 1953, paratypes, male and female (SMF). 81 – G. opalinus Régimbart, 1883, syntype male and labels (MNHN).

Figs 39–40. SEM images of the pronotum showing sculpturing of wrinkles and riffles of the lateral margins, arrows indicate pronotal transverse crease. 39 – Gyrinus venezolensis Ochs, 1953. 40 – G. vinolentus sp. nov.

Figs 29–33. Dorsal and lateral view of the aedeagus of Neogyrinus species, not to scale. 29 – G. ovatus Aubé, 1838. 30 – G. sabanensis sp. nov. 31 – G. guianus Ochs, 1935. 32 – G. rozei Ochs, 1953.