Platynectes malaita, Hájek & Šťastný & Hendrich & Balke, 2023

Hájek, Jiří, Šťastný, Jaroslav, Hendrich, Lars & Balke, Michael, 2023, A review of the genus Platynectes from the Solomon Islands (Coleoptera: Dytiscidae: Agabinae), Acta Entomologica Musei Nationalis Pragae 63 (1), pp. 57-74 : 65-66

Platynectes malaita sp. nov.

( Figs 4 , 11 )

Type locality. Solomon Islands, Malaita, Hahorarumu Uru tribal area, ca. 1.5 km NW of Waisisi village, ca. 09°18.1′S, 161°05.2′E, ca. 45 m a.s.l. Type material. HOLOTYPE: J ( NMPC), labelled: ‘South Pacific, Solomon Is. / MALAITA I., south coast / Hahorarumu Uru Tribal Area / (conservation area), 100-250m / 7.-13.XII.2017, St. Jákl leg. [p] // HOLOTYPE J / PLATYNECTES / malaita sp. nov. / J. Hájek et al. det. 2021 [p, red label]’. PARATYPES: 1J 4♀♀, same label data as holotype ( JSCL, NMPC, ZSMG). 3 ♀♀, ‘ SOLOMON ISLANDS / MALAITA Is., cca 6 km NW /

Waisisi vill. env., 340m / 09°29.8’S 159°59.5’E [sic!] / J.Horák leg., 5.-11. xii.2017 [p]’ ( NMPC).All paratypes with the respective red printed label.

Description. Male holotype. Habitus. Broadest before elytral midlength; body outline continuous.

Colouration ( Fig. 4 ). Head with orange-brown clypeus, round orange spot medially on frons and two spots on vertex; appendages orange-brown. Pronotum with narrowly orange-brown sides and orange anterior corners; basal margin somewhat reddish translucent. Elytron black with brownish lateral margin and epipleura, disc with distinct yellowish pattern consisting of lateral subbasal spot, lateral postmedial spot in two thirds of elytral length, subapical spot, and thin sublateral line in apical half; subbasal spot round, postmedial and subapical spots transverse, connected with sublateral line. Legs orange-brown. Ventral surface brown-blackish, prosternum, median part of metacoxae and metacoxal processes reddish-brown.

Head ca. 0.63× width of pronotum, transversely elliptical. Meshes of reticulation often incomplete (not closed).

Pronotum. Reticulation similar to that of head; meshes larger, often incomplete and less impressed on disc, becoming smaller, closed and deeply impressed near sides. Microreticulation absent. Centre of pronotal disc with small fossa.

Elytra. Punctation double; coarse punctures present in two discal and two lateral, badly perceptible longitudinal lines; fine punctures occurring mostly on lines of reticulation. Reticulation similar to that of head and pronotum but slightly less impressed, consisting of heterogeneous polygonal meshes; meshes mostly complete. Traces of microreticulation hardly perceptible in apical half of elytra.

Ventral surface. Medial part of metaventrite with sparse fine punctation. Ratio WC/WS = 4.2. Metacoxal lines incomplete anteriorly, slightly diverging anteriorly. Metacoxal plates reticulated with polygonal meshes, punctation consisting of sparse fine punctures. Abdominal ventrites with bunch of coarse setigerous punctures present in centre of ventrites III–V, additional setigerous punctures arranged sparsely in transverse line in medial part of ventrites; fine punctures distributed sparsely and irregularly on ventrite surface.

Male genitalia. Median lobe ( Fig. 11a ) in lateral aspect slender in median part, only slightly widened to apex; apex broadly rounded, distinctly setose on ventral side. Parameres ( Fig. 11b ) narrowly triangular, slender, incised basally; dorsal surface densely setated; apical lobe long.

Female. Identical to male in habitus.

Measurements. TL: 5.5–6.1 mm (mean value: 5.85 ± 0.15 mm); holotype: 5.9 mm. TL-h: 4.9–5.5 mm (mean value: 5.25 ± 0.15 mm); holotype: 5.3 mm. MW: 3.1–3.5 mm (mean value: 3.30 ± 0.10 mm); holotype: 3.25 mm.

Variability. The specimens of the type series vary only in shape and size of yellow elytral markings.

Differential diagnosis. So far the only Platynectes known from Malaita Island. From similar and presumably closely related species from Guadalcanal, P. malaita sp. nov. can be recognized by combination of small body size, distinctive dorsal surface pattern ( Fig. 4 ) and the shape of male genitalia ( Fig. 11 ). Actually, we cannot exclude the possibility that P. malaita sp. nov. represents only an isolated population of P. lunga sp. nov. with just slightly smaller body size and more extensive dorsal surface colouration. Indeed, the body size of both species overlaps, dorsal colouration of P. malaita sp. nov. can be interpreted as an extension of that of P. lunga sp. nov., and the shape of median lobe of aedeagus is almost identical in both species. However, the difference in mean value of body length is significant (6.25 ± 0.20 mm in P. lunga sp. nov., but only 5.85 ± 0.15 mm in P. malaita sp. nov.), and the colour pattern of both species is stable with only minor variability which do not overlap. In addition, based on our experience, lotic Platynectes species have only limited spreading abilities, and their distribution is usually limited to small area; therefore, we prefer to keep P. malaita sp. nov. as separate distinct species here.

Etymology. The new species is named after its area of occurrence – Malaita Island. The specific epithet is a noun in the nominative singular, standing in apposition.

Collecting circumstances. The specimens of the type series were collected in a small forest stream (S. Jákl, pers. comm.).

Distribution. The new species is so far known only from the small area around Waisisi bay in Malaita Island ( Fig. 25A ).

Figures

Figs 4–6. Habitus of Platynectes in dorsal (a) and frontolateral (b) view. 4 – P.malaita sp. nov.; 5 – P.mbaole sp. nov.; 6 – P.owaraha sp. nov. Not to scale.

Figs 8–11. Male genitalia of Platynectes. 8 – P. barana sp. nov.; 9 – P. lunga sp. nov.; 10 – P. makira sp. nov.; 11 – P. malaita sp. nov. a – median lobe in lateral view; b – parameres. Scale bar = 0.5 mm.

Fig. 25. Distribution of Platynectes species in the Solomon Islands (A) and Vanuatu (B).