Ranatra bisaya, Tran & Zettel, 2021

Tran, A. D. & Zettel, H., 2021, Taxonomic review of the Ranatra gracilis group sensu Lansbury, 1972 (Nepomorpha: Nepidae), with descriptions of four new species, Raffles Bulletin of Zoology 69, pp. 45-70 : 52-55

Ranatra bisaya , new species

( Figs. 1B , 3 )

Material examined. Holotype (male): “ Philippines: Masbate Isl. \ 3.5 km SE Masbate, Tugbo \ Tugbo River , \ leg. H. Zettel ” ( PNM) . Paratypes ( NHMW, UPLB, ZCW, ZRC): PHILIPPINES: Masbate: 2 males, 1 female, same collection data as holotype ; 1 male, 5 females, 3.5 km SE Masbate, Tugbo, Tugbo River . Ticao : 2 males, 1 female, Monreal, Real, Matang, Tubig Spring; 1 female, W San Fernando, Mag-Kaipit Spring. Guimaras : 1 male, Jordan, San Miguel, Mococo Falls .

Description. General colouration: mostly light brown to brown; eyes dark brown; all coxae brown; fore femur light brown to brown; fore tibia and tarsus yellowish, tip of tarsus brown; middle and hind femora and tibiae weakly annulated brown and yellow; apices of middle and hind tibiae, middle and hind tarsi dark brown. Hemelytra brown, uniformly textured.

Measurements. Males: body length 33–35 (holotype: 34); length of siphon 10.9–12.6 (holotype: 12.3); width of head 2.84–2.97 (holotype: 2.91); interocular width 1.04–1.07 (holotype: 1.05); width of eye 0.89–0.96 (holotype: 0.93); pronotal length 9.35, anterior pronotal length 7.5; posterior pronotal length 3.2; anterior width of pronotum 2.31; posterior width of pronotum 2.91; lengths of leg segments: fore leg: coxa 6.00, femur 9.66, tibia 3.50, tarsus 0.75; middle leg: femur 14.2, tibia 14.5, tarsus 2.02; hind leg: femur 14.5, tibia 17.8, tarsus 2.12.

Females: body length 39.0; length of siphon 12.4–12.8; width of head 3.12–3.18; interocular width 1.10–1.13; width of eye 1.01–1.03; pronotal length 10.1, anterior pronotal length 8.0; posterior pronotal length 3.5; anterior width of pronotum 2.49; posterior width of pronotum 3.07; lengths of leg segments: fore leg: coxa 6.42, femur 10.09, tibia 3.67, tarsus 0.8; middle leg: femur 15.3, tibia 14.6, tarsus 2.18; hind leg: femur 15.2, tibia 17.7, tarsus 2.28.

Head ( Fig. 3B, C ): Vertex raised above eyes with an acute tubercle, narrow in dorsal view; width of eye clearly less than interocular width; clypeus smooth and convex, in lateral view about as high as lora and slightly surpassing lora anteriorly; lora swollen, with a small, but distinct dorsal nodule, bearing sparse, long, pale setae along dorsal side, similar setae also on vertex. Antenna ( Fig. 3A ): finger-like projection of second antennal segment about 0.4× the length of third segment.

Thorax (in both sexes): Prothorax distinctly longer than fore coxa (about 1.5× the length of fore coxa) and subequal to or slightly shorter than fore femur (0.96–1.01× the length of fore femur); anterior lobe about 2.1–2.4× as long as posterior lobe; anterior collar of pronotum distinctly raised and bituberculate; ratio of posterior width / anterior width 1.18–1.26; posterior lobe with humeri broadly rounded, on each sublateral side with two swellings separated by a longitudinal groove ( Fig. 3B, C ). Scutellum with length ca. 1.91–2.19× width, usually swollen at midpoint, then transversely depressed before posterior third, apex pointed. Prosternum with paired broad, shallow longitudinal depressions separated by low and blunt median carina; median carina rather indistinct on posterior half. Mesosternum with pair of low tubercles on anterior margin, posterior half with distinct longitudinal groove. Metasternum with anterior part grooved along midline, posterior part distinctly raised along midline and grooved sublaterally; posterior margin angularly emarginated ( Fig. 3F ). Space between middle coxae subequal to or slightly greater than that between hind coxae. Hemelytra: membrane reaching about mid-length of abdominal tergum VI.

Legs: Fore femur ( Fig. 3D, E ): in both sexes relatively slender (ratio of length / maximum width of femur: 11.3–12.8, holotype 12.4), widest at basal part, ratio of maximum width at basal part / maximum width at distal part in males: 1.22–1.31 (holotype 1.25), in females: 1.31–1.41; flexor side with a carina at ca. 0.4 distal part of femur, bearing dense short setae and a tooth on mesal (= anterior) surface situated distally of carina; distal part with a pair of small teeth on either side of flexor side, proximal to sinuous pre-apical ventral margin, distal teeth clearly longer than surrounding setae on flexor side of femur (more prominent in females); ratio of width of femur across median tooth (excluding tuft of setae) / width of femur at basal part: 1.00–1.08 (holotype 1.05); ratio of width of femur across median carina (excluding setae) / width of femur at basal part: 0.72–0.86 (holotype: 0.83). Middle femur slightly shorter than hind femur. Hind femur, when folded back parallel to body at most reaching posterior third of abdominal sternum VI (in males) or about middle of sternum VI (in females). Middle tibia in males, slightly longer than middle femur, in females slightly shorter than middle femur; hind tibia in both sexes longer than hind femur; middle and hind tibiae both bearing dense fringes of long hairs on posterior margins along their distal two-thirds.

Abdomen: Operculum of male slightly shorter than connexivum, medially keeled, apex pointed. Sternum VI of female with median keel distinctly raised at posterior half. Operculum of female clearly longer than connexivum, surpassing the apex of connexivum of about a quarter to a third the length of operculum. Respiratory siphon about equal to or slightly shorter (0.91–1.03×) than the length of sterna III–V combined, with sparse long, thin hairs along its length, denser towards apical end of siphon.

Male genitalia: Paramere ( Fig. 3G, H ): thickest at basal half, constricted at ca. distal third; ventral margin gradually tapering from middle part towards the constricted part, then followed by a small, sub-triangular process bearing tuft of setae; from inner view, pre-apical process appearing subrectangular due to a small round projection shorter than the tuft of setae; apical hook short and stout, nearly straight with rounded tip; dorsal surface of paramere slightly convex at distal third. Phallotheca strongly sclerotised.

Etymology. The epithet “bisaya” means “inhabitant of the Visayas” in the Visayan language; it is a noun in apposition.

Remarks. The general shape and structures of this new species are relatively similar to those of R. stali , particularly the apex of the paramere, including its pre-apical tooth and apical hook. However, detailed studies on the structures of the paramere show distinct differences. In R. stali , the paramere is dorso-ventrally thicker, with the dorsal margin straight basally, the distal part curved more downwards, and with a narrower gap between the apical hook and pre-apical process. In R. bisaya , new species, the paramere is more slender, with the dorsal margin slightly more sinuate on the basal two-thirds, and with the distal part nearly straight. Other structural differences between R. bisaya , new species, and R. stali are as follows. The respiratory siphon of R. bisaya is slightly shorter, at most 1.0× combined length of sterna III–V (1.0–1.2× in R. stali ). Ranatra bisaya has greater relative lengths of the pronotal length vs. fore coxa length (1.56–1.57 in R. bisaya , new species; 1.34–1.52 in R. stali ). In R. bisaya , the hind femur of the male is at most reaching two-thirds of the distance along sternum VI (in R. stali , the hind femur of the male reaches to the posterior margin of sternum VI). Ranatra bisaya has longer hemelytra, reaching to about middle of abdominal tergum VI, while those of R. stali only reach to the anterior third of tergum VI. In addition, the fore femur of R. bisaya is slightly more robust than that of R. stali , with the ratio of fore femur length to width being about 12.1–12.8 (in males), 11.3–11.6 (in females) in R. bisaya (in R. stali : 12.7–13.3 in males, 11.4–12.2 in females).

For further comparative notes, see Remarks under R. pangantihoni , new species.

Distribution. Philippines: Greater Visayas region: Masbate, Ticao, Guimaras.

Figures

Fig. 1. Habitus of Ranatra spp., all males. A, R. stali Montandon, 1905; B, R. bisaya, new species; C, R. bendanilloi, new species; D, R. brevicauda, new species; E, R. pangantihoni, new species (all of same scale).

Fig. 3. Ranatra bisaya, new species, male. A, antenna. B, C; head and prothorax, lateral and dorsal views; D, E, fore femur, lateral and mesal views; F, metasternum; G, paramere, lateral view; H, apical part of paramere, inner view. (B, C same scale; D, E same scale; G, H same scale).