Ranatra palawanensis, Tran & Zettel, 2021

Tran, A. D. & Zettel, H., 2021, Taxonomy of the Ranatra biroi group sensu Lansbury, 1972 (Nepomorpha: Nepidae), with descriptions of two new species, Raffles Bulletin of Zoology 69, pp. 507-521 : 514-516

Ranatra palawanensis , new species

( Fig. 3 )

Material examined. Holotype (male): “ Philippines: Palawan Prov. / Busuanga Island / 13 road-km WNW Coron / Balulu Falls , leg. H. Zettel ” ( PNM).

Paratypes: 7 males, 5 females, same locality data as holotype ( CZW, NHMW, UPLB, ZRC) .

Description. General colouration ( Fig. 3A ): mostly yellowish brown to brown; eyes dark brown; all coxae yellowish, fore coxa darker; other leg segments mostly yellowish brown, darker at apex. Hemelytra uniformly textured, yellowish or brown.

Measurements: Male: body length 22.0–23.5 (holotype 23.0); length of siphon 17.0–22.0 (holotype 17.0); width of head 2.33–2.43 (holotype 2.36); interocular width 0.70–0.78 (holotype 0.75); width of eye 0.81–0.86 (holotype 0.81); pronotal length 5.79, anterior pronotal length 4.17; posterior pronotal length 2.58; anterior pronotal width 1.55; posterior pronotal width 2.19; lengths of leg segments: fore leg: coxa 5.75, femur 8.50, tibia 3.04, tarsus 0.65; middle leg: femur 13.20, tibia 13.50, tarsus 1.89; hind leg: femur 12.02, tibia 14.30, tarsus 1.94.

Females: body length 23.5–24.5; length of siphon 15.0–21.0; width of head 2.49–2.59; interocular width 0.78–0.83; width of eye 0.84–0.88; pronotal length 5.92, anterior pronotal length 4.25; posterior pronotal length 2.67; anterior pronotal width 1.58; posterior pronotal width 2.25; lengths of leg segments: fore leg: coxa 6.00, femur 8.83, tibia 3.38, tarsus 0.60; middle leg: femur 12.40, tibia 14.25, tarsus 1.99; hind leg: femur 12.25, tibia 14.50, tarsus 1.92.

Head ( Fig. 3B, C ): Vertex raised above eyes into low, conical tumescence; width of eye slightly greater than interocular width; clypeus smooth and flat, higher than lorum and clearly surpassing lorum anteriorly; lorum with rounded dorsal margin, bearing sparse, long, pale setae, similar setae also on vertex. Antenna ( Fig. 3D ) with finger-like projection of second segment about three-quarters the length of third segment.

Thorax: Pronotal length slightly shorter than or subequal to fore coxa (0.92–1.01× the length of fore coxa) and about 0.64–0.69× the length of fore femur; anterior lobe about 1.41–1.82× as long as posterior lobe; anterior collar of pronotum slightly raised; ratio of posterior width / anterior width 1.35–1.46; posterior lobe with humerus broadly rounded, with a sublateral longitudinal groove bordered by a lateral swelling ( Fig. 3B, C ). Scutellum with length ca. 1.5–1.9× width, slightly swollen in anterior two thirds, followed by two sublateral depressions before posterior third, apex pointed. Prosternum anteriorly with paired broad, shallow longitudinal depressions separated by a median carina; median carina extending to base of a broad U-shaped depression on posterior section. Mesosternum with concave anterior margin, flat anterior part, middle part grooved along midline, before a narrow posterior projection between middle coxae. Metasternum with anterior part weakly grooved along midline, posterior part weakly raised along midline, posterior margin straight or slightly emarginated ( Fig. 3E ). Space between middle coxae about same as space between hind coxae. Hemelytra with membrane slightly surpassing posterior margin of abdominal tergum VI.

Legs: Fore femur ( Fig. 3B ) in both sexes slender, widest at basal part, ratio of maximum width at basal part / maximum width at distal part in male 1.45–1.61 (holotype 1.45), in females 1.55–1.73; ventral margin with two subtriangular teeth at distal 0.4 of femoral length, larger tooth on outer surface, smaller tooth on mesial surface situated slightly nearer to apex of femur than larger tooth; ratio of width of femur across larger tooth (excluding tuft of setae) / width of femur at basal part 0.88–0.96 (holotype 0.95); ratio of width of femur across smaller tooth (excluding setae) / width of femur at basal part 0.62–0.73 (holotype 0.71). Middle femur slightly longer than hind femur; hind femur, when folded back parallel to body, slightly surpassing apex of operculum. Middle tibia longer than middle femur; hind tibia longer than hind femur; middle and hind tibiae both bearing dense fringes of long setae on posterior margins along nearly their entire lengths.

Abdomen: Operculum of male about as long as connexivum, medially keeled, apex narrowly rounded. Operculum of female also about as long as connexivum. Respiratory siphon about 0.6–0.9× body length, and about 1.86–2.69× length of sterna III–V combined, with dense, long, thin setae along ventral margin at ca. basal third.

Male genitalia: Paramere ( Fig. 3F ) dorso-ventrally constricted at distal quarter, ventral margin with a low, broad elevation before finger-like apical hook, tip of hook evenly rounded. Phallotheca strongly sclerotised.

Etymology. This species is named after its type locality, Palawan Island.

Remarks. In the R. biroi group, this new species is most similar to R. nieseri in the general appearance of the parameres and most other morphological features, but it differs from the latter in having the space between the middle coxae about as wide as the space between the hind coxae (in R. nieseri , the space between the middle coxae is distinctly narrower), and the apical hook of the paramere has an evenly rounded tip (truncate in R. nieseri ).

Ranatra palawanensis , new species, can be separated from a similar subspecies, R. longipes longipes , by the following characteristics: the paramere is dorso-ventrally constricted before the apical hook (whereas in R. longipes longipes , the dorsal margin is mostly straight and the ventral margin before the apical hook is gradually constricted), and the posterior margin of the metasternum is straight or slightly emarginated (it is convex or rounded in R. longipes longipes ) ( Figs. 3F , 4A ). Ranatra longipes longipes is widespread in Southeast Asia and reaches northwards of Borneo (see below). Specimens from Luzon reported as “ Ranatra diminuta ” by Polhemus & Reisen (1976) might belong either to R. longipes longipes or to one of the new species; however, the material was not available to us.

Distribution. Philippines: Palawan.

Figures

Fig. 3. Ranatra palawanensis, new species, male paratype. A, habitus; B, head, prothorax, and fore legs, dorsal view; C, head and prothorax, lateral view; D, antenna; E, metasternum; F, left paramere, lateral view. B, C same scale.

Fig. 4. Parameres of Ranatra species. A, R. longipes longipes, from Brunei; B, R. cardamomensis, from Natuna Island (ZRC_ ENT00013061); C, R. cardamomensis, from southern Thailand (ZRC_ENT00013063). B, C same scale. Note that the paramere hook of the Thai specimen (Fig. 4C) recurved further after being dry-mounted from an alcohol-preserved specimen; while still in alcohol, the apex was same as that in the type specimens.