Gyrinus (Neogyrinus) guianus Ochs, 1935

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 : 490-493

Gyrinus (Neogyrinus) guianus Ochs, 1935

( Figs 4 , 22–23 , 25–26 , 31 , 54 , 70 , 72 , 76–77 )

Gyrinus guianus Ochs, 1935b: 34 (original description). Gyrinus (Neogyrinus) guianus: OCHS (1935b) : 34 (new status). Gyrinus (Neogyrinus) amazonicus Ochs, 1958 (original description), syn. nov.

Type localities. Gyrinus guianus : ‘Britisch-Guiana, N.W. District’. Gyrinus amazonicus : ‘Lago Irucanga, Igarapé Sahida’ [Amazonas, Brazil].

Type material. Gyrinus guianus : HOLOTYPE: ♀, ( Fig. 77 ) ‘ Type [white disc, red outline, typed black ink]’ ‘BR. GUIANA / North West District / March 1934 / F. A. Squire [white label, partially typed, partially handwritten, all in black ink]’ ‘ Pres. by / Imp.Inst.Ent. / B.M. 1935-40. [white label, typed black ink]’ ‘ Gyrinus / guianus / Ochs / Type! 1934 [handwritten in black ink, handwriting G. Ochs’] ’. PARATYPE ♀ pinned same as holotype except: ‘Co-type [white disc, yellow border, typed black ink]’ and without Och’s handwritten type label ( BMNH).

Gyrinus amazonicus : PARATYPES (2 spec.): J ( Fig. 76 ), pointed with microvial ‘ BRAZIL: Amazonas / Igarapé Sahida / Lago Irucanga / 7.xi.1947. R.Braun. [white label, typed blacked ink]’ ‘Brit. Mus. / 1958-562 [white label, typed black ink, except 562 handwritten in black ink]’ ‘ Gyrinus / amazonicus / Para. Ochs / typen 1958 [white label, handwritten in blue ink, handwriting Ochs’]’ ( BMNH). J pointed, same as previous except ‘Igarapé Grande do Jurucui, 27.xi.1947 ’ ( BMNH).

Other material examined. VENEZUELA: AMAZONAS: ca. 7 km S. Samariapo , 5°10.900’N, 67°46.078’W, 95 m, 15.i.2009, leg. Short, Miller, García, Camacho, & Joly, roadside pond, VZ09-0115-02X, SM0846154 (1 spec. SEMC) ; Puerto Ayacucho (29 km S) Rio Paris Chico , seined, leg. J.T.Polhemus, CL2372 (1 spec. USNM) ; same as previous except: 66 km N Rio Herera , i.25.1989, CL2385 (1 spec. USNM) ; nr Iboruwa, ‘ Tobogancito’ , 5°48.414’N, 67°26.313’W, 13.i.2009, leg. Short / Miller, VZ 09011302 (9 spec. KBMC) ; Pond 7km S Samariapo, 5°10.900’N, 67°46.078’W, 15.i.2009, leg. Short / Miller,VZ09011502 (14 spec. KBMC) ; riv.nr Orinoco / Sipapo confl., 5°03.707›N, 67°46.768›W, 15.i.2009, leg. Miller / Short, VZ 09011501 (32 spec. KBMC) ; riv nr Orinoco / Sipapo confl., 5°03.707’N, 67°46.768’W, 15.i.2009, leg. Short / Miller, VZ 09011504 (1 spec. KBMC) ; Stream along Rio Sipapo , 4°55.849’N, 67°44.645’W, 16.i.2009, leg. Short / Miller, VZ09011602 (6 spec. KBMC) ; sameas previous except 87 m, 16.i.2009, leg. Short, García, Camacho, Miller, & Joly, VZ 09-0116-02X, SM0845691 (1 spec. SEMC) ; San Carlos de Rio Negro , 24.i.1985, leg. P. & P. Spangler, R. Faitoute, W. Steiner (1 spec. USNM) .

Diagnosis. Body form ( Fig. 4 ) narrowly oval, weakly convex in lateral view; pronotal lateral margins dark in color, elytral lateral margins often dark in color, other times red; elytral disc with mostly uniform reticulation, bronzy-metallic in appearance; striae VI–XI evident ( Fig. 22 ) with distinct linearpunctures ( Fig. 26 ), striae VI–X sulcate ( Fig. 22 ); elytral intervals all evenly convex; elytra medially with medial pre-apical plica ( Fig. 23 ); elytral apex rounded ( Fig. 23 ), without border, epipleural indistinct; metanepisternal ostiole absent; aedeagus ( Fig. 31 ) with median lobe shorter than parameres, narrow, apex strongly triangular; gonocoxae ( Fig. 54 ) elongate, with rounded apices.

Gyrinus guianus is most similar to G. rozei and can primarily be distinguished by the diagnosis given under G. rozei . However, an additional feature unique to G. guianus that will aid in identifying this species is the medial pre-apical plica of the elytra ( Fig. 23 ). Among the Venezuela Neogyrinus species of Venezuela, only G. guianus exhibits this distinguishing elytral feature. The female gonocoxae also easily separate these two species, as G. guianus has more elongate gonocoxae with rounded apices ( Fig. 54 ) compared to the shorter strongly emarginate gonocoxae of G. rozei ( Fig. 55 ).

Redescription. Size. Female length = 4.0– 4.5 mm, width = 2.0– 2.5 mm; male length = 3.5–4.0 mm, width = 2 mm. Habitus. Body form narrowly oval, strongly attenuated anteriorly and posteriorly, widest point at midlength; in lateral view weakly dorsoventrally convex, greatest convexity posterior to scutellar region, evenly depressed anteriorly and posteriorly.

Coloration ( Fig. 4 ). Dorsally, head, pronotum, elytra bronzy-green, lateral margins of pronotum similarly colored as remainder of pronotum, elytral margin often similarly colored as remainder of elytra, other times red; ventrally lightly colored, mouthparts, ventral surface of pedicel, hypomeron, elytral epipleuron, and legs light yellow, remainder of venter slightly darker yellow to orangish-yellow in color.

Sculpture and structure. Pronotum with narrow lateral margins. Elytra ( Fig. 22 ) with stria I–V weakly present, evident only as reticulate stripes ( Fig. 25 ) with irregular, very weakly impressed punctures; striae VI–XI evident, striae VI anteriorly faintly evident anteriorly, posteriorly weakly sulcate with faint linear punctures; stria VII with linear punctures weakly impressed in humeral region, more well impressed and sulcate posteriorly; striae VIII–IX sulcate, linearpunctures ( Fig. 26 ) similarlywell impressed in humeral region and posteriorly; stria Xsulcate only posteriorly; stria XI raised above lateral margin for entirety, lineate in humeral region, punctures distinct in small medial raised region, lineate again posteriorly. Elytral disc with mostly uniform reticulation composed of strongly impressed meshes with round sculpticells ( Fig. 26 ), producing a bronzed appearance; all elytral intervals evenly convex. Elytra with distinct medial pre-apical plica ( Fig. 23 ); apices rounded ( Fig. 23 ); bor- der absent; epipleural angle indistinct, never with denticle. Metanepisternal ostiole absent. Ultimate abdominal tergite without strong acumination.

Male genitalia ( Fig. 32 ). Aedeagus withmedianlobe narrow, shorter than parameres, weakly attenuated apically, parallel sided in apical 1 /3, apex strongly triangular, with lateral margins of apical 1/5 straight, bent at ca. 60  angle; parameres with apex narrowly rounded. Female genitalia ( Fig. 54 ). Gonocoxae elongate, apices rounded, left gonocoxa less curved than right.

Variability. This species is variable in the development of the lateral margin of the elytra. Populations from Amazonas, Venezuela had the lateral margin of the elytra considerably narrower than those exhibited by more easterly populations such as the paratype specimens of G. amazonicus from Amazonas Brazil, or compared to that of the paratype of G. guianus , which have anoticeably broader elytrallateral margin. However, in general, the lateral margin of G. guianus is distinctly narrower than that of other species.

The degree of impression of the pre-apical medial plica of the elytra ( Fig. 23 ) was also noted to vary among specimens, even within a population, with it being quite distinct in most specimens, but less so in others. Despite this, the presence of the plica could still be made out even in specimens where the plica was very weakly impressed.

Habitat. In Venezuela, this species has been collected both in ponds and along rivers and streams ( Fig. 70 ).

Distribution. This species was previously known from western Guyana and northwestern Brazil ( OCHS 1967a), and is now recorded from Venezuela. Within Venezuela this species is found in the Guiana Shield region ( Fig. 72 ).

Discussion. Gyrinus guianus was originally described solely from female specimens from northwestern Guyana ( OCHS 1935b). In 1958 OCHS described G. amazonicus ( Fig. 68 ) from the Amazonian region of northern Brazil and stated it to be most similar to G. guianus . OCHS (1958) suggested his new species could be distinguished from G. guianus by having a different habitus, being wider and less parallel-sided in appearance. However, after examining the holotype of G. guianus ( Fig. 77 ), and comparing it to paratypes of G. amazonicus ( Fig. 76 ), as well as a series of male andfemale specimens from Venezuela ( Fig. 4 ), the two species are identical. Images of the male holotype in the SMF provided via C. Benetti to confirm this. Most tellingly, G. amazonicus ( Fig. 76 ) clearly exhibits the distinct medial pre-apical plica diagnostic of G. guianus ( Figs 23 and 77 ). The differences stated by OCHS (1958) to erect the G. amazonicus , represent very common variation between populations and even among the sexes as females tend to be more elongate than males.

Figures

Figs 1–6. Dorsal habitus of Neogyrinus species, scale bar = 1 mm. 1 – Gyrinus sabanensis sp. nov. 2 – G. gibbus Aubé, 1838 from Amazonian Venezuela. 3 – G. ovatus Aubé, 1838. 4 – G. guianus Ochs, 1935. 5 – G. gibbus ‘var. apicalis’ Sharp, 1877 from Caracas valley, Venezuela. 6 – G. rozei Ochs, 1953.

Figs 22–24. 22–23 – SEM images of G. guianus Ochs, 1935 elytral morphology. 22 – elytron, box indicates region shown in Fig. 23, scale bar = 1 mm. 23 – elytral apex, arrow indicates medial pre-apical plica. 24 – elytron of G. rozei Ochs, 1953, scale bar = 1 mm.

Figs 25–28. SEM images of elytral interval reticulation and strial punctures. 25–26 – G. guianus Ochs, 1935. 25 – intervals II and III, striae I–III. 26 – intervals IX and X, striae VIII–X. 27–28 – G. rozei Ochs, 1953. 27 – intervals II and III, striae I–III. 28 – intervals IX and X, striae VIII–X.

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.

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 68–71. Habitat of Gyrinus species in the Guiana Shield region of Venezuela. 68 – Bolívar State, Gran Sabana, collecting event AS-08-063, habitat of G. rozei Ochs, 1953. 69 – Bolívar State, Gran Sabana, collecting event AS- 08-066, habitat of G. sabanensis sp. nov. 70 – Amazonas, tributary of the Rio Sipapo, collecting event VZ09-0116- 02X, habitat of G. guianus Ochs, 1935 and G. gibbus Aubé, 1838. 71 – Bolívar State, 25 km E. El Burro, collecting event AS-08-077, habitat of G. gibbus.

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).