Exocelina nomax (J. Balfour-Browne, 1939)

Shaverdo, Helena, Surbakti, Suriani, Warikar, Evie L., Sagata, Katayo & Balke, Michael, 2019, Nine new species groups, 15 new species, and one new subspecies of New Guinea diving beetles of the genus Exocelina Broun, 1886 (Coleoptera, Dytiscidae, Copelatinae), ZooKeys 878, pp. 73-143 : 73

15. Exocelina nomax (J. Balfour-Browne, 1939) Figs 36 , 41

Copelatus nomax J. Balfour-Browne, 1939: 65-66; Guignot 1956: 55 (catalogue); Guéorguiev 1968: 34 (catalogue).

Copelatus nomax J. Balfour-Browne, 1939 sensu Guéorguiev 1978: 268-269 (key); Guéorguiev and Rocchi 1993: 148.

Copelatus (Papuadytes) nomax J. Balfour-Browne, 1939: Balke 1998: 334 (notes, diagnosis); Nilsson 2001: 77 (catalogue).

Papuadytes nomax (J. Balfour-Browne, 1939): Nilsson and Fery 2006: 56 (comb. nov.).

Exocelina nomax (J. Balfour-Browne, 1939): Nilsson 2007: 34 (comb. nov.).

Exocelina undescribed sp. MB3405: Toussaint et al. 2014: supplementary figs 1-4, tab. 2; Toussaint et al. 2015: supplementary figs S1, S2, tab. S3, and information S5, S6.

Type locality.

Papua New Guinea: Central Province, Mafulu, ca. 08°30'S, 147°00'E, ca. 1219 m a.s.l.

Type material.

Holotype: female “Type” [round, with red bead], "PAPUA: Mafulu. 4,000ft. i.1934. L.E.Cheesman. B.M.1934-321.", " Copelatus nomax , ♀ Type nov.sp." [hw, the word “type” with red ink], “Holotype” [red] (BMNH).

Additional material.

Central: 23 males, 32 females "Papua New Guinea: Central, Kokoda Trek, 320m, i.2008 [09°] 19.236S 147.31.791E, Posman (PNG 168)", one male with an additional green label "DNA M.Balke 3405" (NHMW, ZSM). 4 males "Papua New Guinea: Central, Kokoda Trek, 980m, i.2008, [09°] 15.933S 147.36.590E, Posman (PNG 169)", one of them with an additional green label "DNA M.Balke 3411" (ZSM). 1 female "Papua New Guinea: Central, Kokoda Trek, 980m, i.2008, [09°] 15.933S 147.36.590E, Posman (PNG 169)", "DNA M.Balke 4117" [green] (ZSM). 10 males, 2 females "Papua New Guinea: Central, Kokoda Trek, 590m, i.2008, [09°] 14.339S 147.36.920E, Posman (PNG 170)" (NHMW, ZSM). 19 males, 31 females "Papua New Guinea: Central, Tapini, 1200m, 31.x.2007, 08.21.557S 146.58.712E, Kinibel (PNG 162)", one of the males with an additional green label "DNA M.Balke 3306" (NHMW, ZSM). 2 males, 3 females "Papua New Guinea: Central, Moreguina [10°'57"S, 148°28'27"E], 16.viii.2008, Posman (PNG 183)", males and one female with additional green labels "DNA M.Balke 3745", "DNA M.Balke 3816", "DNA M.Balke 3746" respectively (ZSM). 5 males, 9 females "Papua New Guinea: Central, Moroka area, Kailaki, 827 m, 26.x.2009, 9.24.134S 147.33.521E, Sagata (PNG225)" (NHMW, ZSM). 14 males, 8 females "Papua New Guinea: Central, Moroka, Kailaki, 827 m, 26.x.2009, 9.24.113S 147.33.524E, Sagata (PNG226)" (NHMW, ZSM). 1 female "Papua New Guinea Central, Moroka, Kailaki Wareaga, 760m, 27x2009 9.25.424S 147.31.068E Sagata (PNG227)" (ZSM). 27 males, 39 females "Papua New Guinea: Central, 755m, 28.x.2009 S9 25 47 5 E147 32 59.1, Sagata (PNG229)" (NHMW, ZSM). National Capital District: 2 males, 3 females "Papua New Guinea: National Capital District, Varirata NP, 600m, 16.xii.2007, 09.26.13S 147.22.09E, Balke & Sagata (PNG 159)", males with additional green labels "DNA M.Balke 3304" and "DNA M.Balke 3305" (ZSM).

Redescription.

Body size and form: Beetle small: TL-H 3.0-3.8 mm, TL 3.45-4.2 mm, MW 1.7-2.15 mm (holotype: TL-H 3.5 mm, TL 3.95 mm, MW 1.95 mm), with oblong-oval habitus.

Colouration: Dark brown, with paler sides of pronotum and head. Head reddish to reddish brown, darker posterior to eyes. Pronotum brown to dark brown on disc and reddish to reddish brown on sides. Elytra uniformly dark brown. Head appendages and legs proximally yellowish, legs distally darker, reddish brown ( Fig. 36 ). Teneral specimen paler.

Surface sculpture: Shiny dorsally, with inconspicuous punctation and weakly impressed microreticulation. Head with fine and sparse punctation (spaces between punctures 1-3 times size of punctures); diameter of punctures smaller than or equal to diameter of cells of microreticulation. Pronotum with finer and sparser punctation than on head. Punctation on elytra finer and sparser than on pronotum, inconspicuous, in some specimens invisible. Disc of pronotum and elytra with weakly impressed microreticulation; head and lateral sides of pronotum with microreticulation stronger. Metaventrite, metacoxae, and abdominal ventrites distinctly microreticulate. Metacoxal plates with longitudinal strioles and weak transverse wrinkles; abdominal ventrites with strioles. Punctation on venter inconspicuous, slightly stronger on two last abdominal ventrites.

Structures: Pronotum with narrow lateral bead. Base of prosternum and neck of prosternal process with distinct ridge, rounded anteriorly. Blade of prosternal process lanceolate, narrow, slightly convex, with distinct bead and few setae laterally. Abdominal ventrite 6 truncate.

Male: Protarsomere 4 with large, thick, strongly curved anterolateral hook-like seta. Protarsomere 5 ventrally with anterior band of ca. 30 and posterior row of nine relatively long setae ( Fig. 41D ). Abdominal ventrite 6 with 7-11 lateral striae on each side. Median lobe slender, without lateral setae apically; in lateral view, evenly curved to broadly pointed, elongate apex; in ventral view, apex slightly truncate, asymmetrical ( Fig. 41A, B ). Paramere very slightly concave on dorsal side, with long and dense subdistal and inconspicuous proximal setae ( Fig. 41C ).

Female: Without evident differences in external morphology from males, except for not modified protarsi and abdominal ventrite 6 without striae.

Notes on identity of the additional material with the holotype, affinities.

Balke (1998: 334) indicates Exocelina nomax as species minus cognitus. However, our study of the material collected from Tapini, village ca. 20 km north to Mafulu, allows us to consider with certain confidence that it belongs to E. nomax . It is the only Exocelina species collected from this area, and it was collected in abundant number (50 specimens) in Tapini. We assume this locality as the most northern distribution border of the species, which is very numerous in Kokoda and Kailaki areas. Morphologically, the specimens from Tapini, Kokoda, Kailaki and Varirata are identical to the holotype ( Fig. 36A, B ). Only three species occur close to Tapini-Mafulu area: E. garaina , E. posmani Shaverdo & Balke, 2016, and E. woitapensis Shaverdo & Balke, 2016 (the E. danae group). But they are larger (TL-H 3.6-4.5 mm), and the smallest of them, E. woitapensis , is matt dorsally. Moreover, E. nomax can be differentiated from them by its narrow pronotal bead, a very characteristic feature. Smaller size and narrow bead of the pronotum can be used to distinguish it from E. jaseminae , a species very similar to it in colour and surface structures. From the other species co-occurring in the Central and National Capital District Provinces ( E. bacchusi , E. pulchella sp. nov., and species of the E. danae and E. jaseminae groups), E. nomax can be distinguished by its body size and colouration, dorsal punctation and microreticulation, narrow pronotal bead, and shape and setation of its median lobe and paramere. See also under E. warahulenensis sp. nov. and “Key”.

The specimen from Telefomin (Sandaun Province), 1 male "PAPUA, Selminumtem [Selminum Tem, 45 km SWS Telefomin, ca. 5°S; 141°15'E], W.Sepik d. P.Beron leg.", " Copelatus nomax J.B.Br. det.V. Guéorguiev 1917" [partly hw] (NHMW), which was identified by Guéorguiev & Rocchi (1993: 148) as E. nomax and indicated by Balke (1998: 334, 338) as "sp. 4" has been recently described under the name E. okbapensis Shaverdo & Balke, 2017 ( Shaverdo et al. 2017).

Distribution.

Papua New Guinea: Central and National Capital District Provinces ( Fig. 45 ). The species is known from numerous specimens in the Central Province and a small population in the National Capital District.

Figures

Figure 45. Map of the eastern part of New Guinea showing distribution of the species of the E. larsoni and takime groups.

Figures 35 - 39. Habitus and colouration 35 Exocelina larsoni (Balke, 1998) 36 E. nomax (J. Balfour-Browne, 1939) A holotype B specimen from Tapini 37 E. warahulenensis sp. nov. 38 E. mianminensis sp. nov. 39 E. takime (Balke, 1998).

Figures 41, 42. 41 Exocelina nomax (J. Balfour-Browne, 1939) 42 E. warahulenensis sp. nov. A median lobe in ventral view B median lobe in lateral view C paramere in external view D male protarsomeres 4 - 5 in ventral view.