Ranatra luzonensis, 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 : 513-514

Ranatra luzonensis , new species

( Fig. 2 )

Material examined. Holotype (male) “ Philippines: Luzon / Cagayan Province / Gonzaga, Pateng / leg. C. V. Pangantihon ” ( PNM).

Paratypes: 1 female, same locality data as holotype ( CZW) ; 1 female, Philippines, Cagayan, Peñablanca, Barangay Quibal, Pinacanauan River , 17°42.581′N, 121°48.644′E, 40 m a.s.l., coll. T. Naruse & J. C. E. Mendoza, 25 April 2007, JCEM 07-010 ( ZRC) ; 1 male, Philippines, Nueva Ecija, coll. R. Abalos, 13 October 1951 ( SEMC) .

Description. General colouration ( Fig. 2A ): mostly light brown to brown; eyes dark brown; all coxae yellowish, fore coxa darker; fore femur mostly yellowish; middle, hind femora and tibiae weakly annulated brown and yellow; fore tarsus yellowish brown, darker at apex; apices of middle and hind femora, middle and hind tarsi dark brown. Hemelytra uniformly textured, yellowish or brown.

Measurements: Male (holotype): body length 25.0; length of siphon 18.0; width of head 2.59; interocular width 0.75; width of eye 0.92; pronotal length 6.00, anterior pronotal length 4.58; posterior pronotal length 2.58; anterior pronotal width 1.66; posterior pronotal width 2.28; lengths of leg segments: fore leg: coxa 6.67, femur 9.67, tibia 3.33, tarsus 0.72; middle leg: femur 13.40, tibia 16.50, tarsus 2.20; hind leg: femur 13.30, tibia 16.00, tarsus 2.25.

Females: body length 28.0–29.0; length of siphon 21.0–22.0; width of head 2.80–2.90; interocular width 0.88; width of eye 0.96–1.01; pronotal length 6.75, anterior pronotal length 5.00; posterior pronotal length 3.17; anterior pronotal width 1.89; posterior pronotal width 2.75; lengths of leg segments: fore leg: coxa 7.50, femur 10.90, tibia 3.75, tarsus 0.72; middle leg: femur 15.40, tibia 17.10, tarsus 2.23; hind leg: femur 15.30, tibia 17.30, tarsus 2.23.

Head ( Fig. 2B, C ): Vertex raised above eyes but without tubercle; width of eye clearly greater than interocular width; clypeus smooth and flat, higher than lorum and clearly surpassing lorum anteriorly; lorum swollen, with slightly angular dorsal margin, bearing sparse, long, pale setae, similar setae also on vertex. Antenna ( Fig. 2D ) with fingerlike projection of second antennal segment about two-thirds the length of third segment.

Thorax: Pronotal length shorter than fore coxa (about 0.9× the length of fore coxa) and about 0.6× the length of fore femur; anterior lobe about 1.58–1.78× as long as posterior lobe; anterior collar of pronotum slightly raised in lateral view; ratio of posterior width / anterior width 1.37–1.46; posterior lobe with humerus broadly rounded, with a sublateral longitudinal groove bordered by a lateral swelling ( Fig. 2B, C ). Scutellum with length ca. 1.85–2.11× width, anterior two thirds slightly swollen, 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 U-shaped depression on posterior section. Mesosternum with concave anterior margin, flat anterior part, middle part grooved along midline, before narrow posterior projection between middle coxae. Metasternum with anterior part weakly grooved along midline, posterior part weakly raised along midline, posterior margin slightly emarginated ( Fig. 2E ). Space between middle coxae much narrower (less than 0.5×) than space between hind coxae. Hemelytra with membrane slightly surpassing posterior margin of abdominal tergum VI.

Legs: Fore femur ( Fig. 2B ): in both sexes slender, widest at basal part, ratio of maximum width at basal part / maximum width at distal part in male (holotype) 1.55, in females 1.66–1.77; 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 more anteriorly than larger tooth; ratio of width of femur across larger tooth (excluding tuft of setae) / width of femur at basal part 0.77–0.86 (holotype 0.81); ratio of width of femur across smaller tooth (excluding setae) / width of femur at basal part 0.65–0.75 (holotype 0.75). Middle femur about as long as hind femur; hind femur, when folded back parallel to body, reaching about anterior two-thirds operculum. Middle tibia slightly 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 ( Fig. 2F ) about as long as connexivum, medially keeled, apex narrowly rounded. Operculum of female also about as long as connexivum. Respiratory siphon about 0.7–0.8× body length, and about 2.0× length of sterna III–V combined.

Male genitalia: Paramere ( Fig. 2G ) dorso-ventrally thickened at middle part, constricted at distal third basad of apical hook; inner margin of hook with a triangular tooth-like elevation; tip of hook expanded; dorsal surface of paramere almost straight, slightly concave at basal two thirds. Phallotheca strongly sclerotised.

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

Remarks. In the R. biroi group, four species, namely R. biroi , R. natunaensis , R. rafflesi , and R. luzonensis , new species, are probably closely related based on the presence of a pointed, tooth-like elevation on the inner margin of the paramere apical hook. They are separable using characters in the key above.

The paramere of R. luzonensis , new species, appears most similar to that of R. biroi in the distinctly expanded tip of the apical hook and the more obtuse tooth-like elevation on its inner margin. However, other aspects of the paramere show distinct differences between two species: in R. luzonensis , the basal part is dorso-ventrally thicker (it is more slender in R. biroi ), the dorsal surface at the distal part has a sulcate area restricted to the area above the apical hook (the sulcate area is located on distal third in R. biroi ), and the ventral margin is more gradually tapering towards the sub-apical tooth (it is more abruptly constricted at distal third in R. biroi ). In addition, this new species has the following differences from R. biroi : the vertex is visible when viewed laterally, clearly higher than the eyes (in R. biroi , the vertex is lower than the eyes in lateral view), the posterior margin of the metasternum is narrower (more truncate in R. biroi ), the median carina of sternum VI of the female is not distinctly raised posteriorly (in R. biroi , it is distinctly raised towards the posterior margin), and the operculum in both sexes reaches the apex of the connexivum (in R. biroi , the operculum usually does not reach the apex of the connexivum).

Distribution. Philippines: northern Luzon (Cagayan and Nueva Ecija provinces).

Figures

Fig. 2. Ranatra luzonensis, new species, male holotype. A, habitus; B, head, prothorax, and fore legs, dorsal view; C, head and prothorax, lateral view; D, antenna; E, metasternum; F, operculum; G, left paramere, lateral view. B, C same scale; E, F same scale.