Ranatra pangantihoni, 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 : 61-63

Ranatra pangantihoni , new species

( Figs. 1E , 7 , 8 )

Material examined. Holotype (male): “ Philippines: Nueva Viscaya \ Santa Fe , Imugan, stream \ at Imugan Falls, 1000m / leg. H. Zettel ” ( PNM).

Paratypes ( ADMU, NHMW, UPLB, VPGC, ZCW, ZRC): PHILIPPINES: Luzon : 4 males, 2 females, Nueva Viscaya Province, same locality data as holotype ; 4 males, 3 females, Ilocos Norte Province, Carasi, Cura River ; 1 male, 1 female, Ilocos Norte Province, Carasi, Nagoboban Creek , in forest ; 4 males, 1 female, Ilocos Norte Province, Solsona , stream below waterfall ; 1 male, Ilocos Norte Province, Solsona, Gasgas River ; 1 male, La Union Province, Bacnotan, Don Mariano Marcos Memorial State University, NARTDI Falls ; 1 male, 3 females, Nueva Viscaya Province, Santa Fe, Malico, Inacio, Inacio River , 1,200 m a.s.l. ; 3 males, 1 female, Nueva Viscaya Province, Santa Fe, Malico, Dulipay River ; 1 male, Nueva Viscaya Province, Santa Fe, Malico , small creek ; 1 male, Nueva Viscaya Province, Imugan, Maliko River ; 1 male, Kalinga Province, Balbala, 1 km northwest of Balbalasang, Ibong River , 950 m a.s.l. , 17°29′N, 121°02′E; 2 males, 2 females, Isabela Province, San Mariano, Catalangan, River , Digsinan ; 3 males, 1 female, Zambales Province, Subic Bay , “Aeta Village” ; 1 female, Zambales Province, Olongapo, Subic Base, near Riding Stable ; 1 male, Zambales Province, Olongapo, Subic Base, at JEST (“ Jungle Survival ”) ; 4 males, 4 females, Laguna Province, Los Baños, Rest Area, creek below Tampalit Falls ; 1 male, Laguna Province, Los Baños, Mount Makiling, Flat Stones ; 1 female, Languna Province, river at Cavinti, near Pagsanjan ; 2 males, 1 female, Laguna Province, Los Baños, Mount Makiling, Molawin Creek at College of Forestry ; 4 males, 4 females, Laguna, Mount Makiling at Central Forest Experimental Station, near Thermal Spring ; 1 female, Cavite Province, Alfonso, Pajo ; 1 male, Batangas Province, Bauan, Santa Maria ; 1 male, 1 female, Quezon Province, Pagbilao, Iringan ; 1 male, Quezon Province, Atimonan, Quezon NP, Old Zigzag Road. Marinduque : 3 females, Marinduque Province, northeast of Boac, 7 km southeast of Mogpog, Bocboc , Paadyan Falls. Mindoro: 1 male, 1 female, Oriental Mindoro, Roxas, San Vicente, Quirao, Hinundugan tributary, Quirao na Balete Creek , 12°35′36″N, 121°23′36″E, 230 m a.s.l. ; 2 males, Oriental Mindoro, Puerto Galera, Tagbinai Malaki River , small river in secondary vegetation; 13°28′57″N, 120°57′34″E, c. 10 m a.s.l. ; 1 female, Oriental Mindoro, Baco, rural road side, residual pools of small intermittent river in secondary vegetation; 13°21′49″N, 121°05′30″E, c. 26 m a.s.l. Sibuyan: 4 males, 1 female, Romblon Province, Sibuyan Island, San Fernando, España .

Description. General colouration: mostly light brown to brown; eyes dark brown; all coxae brown; all femora and tibiae usually annulated brown and yellow; fore tarsus yellowish brown, with brown apex; apices of middle and hind tibiae, middle and hind tarsi dark brown. Hemelytra uniformly textured, light coloured or brown.

Measurements: Males: body length 33–38 (holotype: 37); length of siphon 9.3–12.7 (holotype: 11.3); width of head 2.79–3.25 (holotype: 3.25); interocular width 1.02–1.25 (holotype: 1.20); width of eye 0.89–1.03 (holotype: 1.03); pronotal length 9.31, anterior pronotal length 7.10; posterior pronotal length 3.60; anterior width of pronotum 2.47; posterior width of pronotum 3.33; lengths of leg segments: fore leg: coxa 6.60, femur 10.5, tibia 5.33, tarsus 0.84; middle leg: femur 15.4, tibia 15.8, tarsus 2.07; hind leg: femur 15.3, tibia 19.2, tarsus 2.28.

Females: body length 38–43; length of siphon 10.1–13.0; width of head 2.96–3.49; interocular width 1.08–1.29; width of eye 0.94–1.11; pronotal length 9.82, anterior pronotal length 7.50; posterior pronotal length 3.70; anterior width of pronotum 2.69; posterior width of pronotum 3.47; lengths of leg segments: fore leg: coxa 6.70, femur 10.6, tibia 4.17, tarsus 0.91; middle leg: femur 16.6, tibia 16.4, tarsus 2.15; hind leg: femur 16.2, tibia 18.8, tarsus 2.20.

Head ( Fig. 7B, C ): Vertex above eyes with an obtuse tubercle, narrow in dorsal view; width of eye clearly less than interocular width; clypeus smooth and convex, in lateral view about as high as or slightly higher than lora and slightly surpassing lora anteriorly; lora swollen, with a small, but distinct dorsal nodule, bearing very few sparse, long, pale setae along dorsal side (nodule less distinct in some samples). Antenna ( Fig. 7A ): finger-like projection of second antennal segment about 0.4× the length of third segment.

Thorax: Prothorax in lateral view distinctly longer than fore coxa (about 1.3–1.5× the length of fore coxa) and about 0.85–1.08× the length of fore femur; anterior lobe about 1.82–2.18× as long as posterior lobe; anterior collar of pronotum distinctly raised and bituberculate; ratio of posterior width / anterior width 1.18–1.42; posterior lobe with humeri broadly rounded, on each sublateral side with two swellings separated by a longitudinal groove ( Fig. 7B, C ). Scutellum with length ca. 1.81–2.04× width, usually swollen at midpoint followed by a transverse depression before posterior third, apex pointed. Prosternum with paired broad, shallow longitudinal depressions separated by a low and blunt median carina; median carina rather indistinct in posterior half. Mesosternum with slightly raised anterolateral margin, posterior projection between middle coxae truncate, weakly grooved along midline. Metasternum with anterior part grooved along midline, posterior part distinctly raised along midline and grooved sublaterally, posterior margin angularly emarginated ( Fig. 7F ). Space between middle coxae subequal to or slightly greater than that between hind coxae. Hemelytra: membrane only reaching anterior third of abdominal tergum VI.

Legs: Fore femur ( Fig. 7D, E ): in both sexes relatively slender (ratio of length / maximum width of femur: 12.0–13.8, holotype 13.6), widest at basal part, ratio of maximum width at basal part / maximum width at distal part in males: 1.09–1.23 (holotype 1.15), in females: 1.13–1.20; 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 to median carina; distal part with a pair of small teeth on lateral surface of margin, proximal to sinuous pre-apical margin; distal teeth slightly longer than surrounding setae on ventral 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: 1.00–1.15 (holotype: 1.12); ratio of width of femur across median carina (excluding setae) / width of femur at basal part: 0.86–0.92 (holotype: 0.90). Middle femur slightly longer than hind femur; hind femur, when folded back parallel to body reaching to about anterior half of abdominal sternum VI (in males) and reaching about anterior third 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 ( Fig. 7G ) about equal to 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 one third the length of operculum. Respiratory siphon clearly shorter than or subequal to (0.71–0.98×) the length of sterna III–V combined, with few sparse long, thin hairs along its length.

Male genitalia: Paramere ( Fig. 8 ): dorso-ventrally thickened at basal third, constricted at distal quarter; distal quarter directed downwards; ventral margin gradually tapering from near middle part towards the constricted part, then followed by an acute trapezoidal process bearing tuft of setae; on inner face, pre-apical process bearing a rounded projection slightly shorter than tuft of setae (except in some specimens from Laguna, projection more prominent, see Fig. 8H, I, K, L ); apical hook slender with narrow, rounded tip; dorsal margin of paramere nearly straight at basal two-thirds, convex at distal third and slightly concave at same section with preapical process (samples from Laguna, Quezon, and Romblon with slight variations in the thicker basal half of paramere, while the curvature of the apical hook and the gap between pre-apical process and apical hook are consistent among populations). Phallotheca strongly sclerotised.

Etymology. This species is dedicated to the entomologist Clister V. Pangantihon from the Ateneo de Manila University who found this species on the island of Mindoro.

Distribution. Philippines: Greater Luzon region: Northern and Central Luzon (Ilocos, Nueva Viscaya, Zambales / Bataan, Laguna, Cavite, Batangas, Quezon), Marinduque; Greater Mindoro region: Mindoro; Sibuyan (region).

Remarks. In the R. gracilis group, five species from the Philippines, R. stali and the four new species, may form a monophyletic clade as they share nearly identical characteristics in regard to the structure of their thoracic sterna (especially the posterior margin of metasternum), the presence of nodules on the lora, the laterally narrow tubercle on the vertex, the distinctly raised posterior half of sternum VI in the female (in lateral view), and the relatively short siphon (not longer than 0.4× the body length). The comparative character states separating these species are summarised in Table 1.

Ranatra stali can be easily separated from the remaining species of the R. gracilis group in the Philippines by having the siphon about equal to or longer than the combined length of sterna III–V, the distal part of paramere clearly curved ventrad, and a narrower space between apical hook and pre-apical process of the paramere.

Among species of the R. gracilis group, R. pangantihoni , new species, is most similar to R. bisaya , new species. Both species have a relatively wide head (ratio of head width to anterior width of pronotum about 1.2–1.3), a more robust fore femur (fore femur length is about equal to or greater than 12.0× width in males, equal to or greater than 11.3× width in females), and an acute trapezoidal pre-apical process ventrally on the paramere. However, the shape of the paramere and its apical hook easily serve to separate these two species.

Ranatra bendanilloi , new species, is most similar to R. brevicauda , new species, in having a more slender fore femur (fore femur length is about equal to or less than 11.5× width in males, equal to or less than 11.1× width in females), relatively narrower head (ratio of head width to anterior width of pronotum about 1.1–1.2), and a long, slender apical hook on the paramere. The dorsal margin of the paramere (nearly straight in R. bendanilloi , sinuate in R. brevicauda ), the shape of pre-apical process of the paramere (broader and sub-triangular in R. bendanilloi , narrower and acute trapezoidal in R. brevicauda ) also serve to separate these two species.

The general form of paramere of R. bendanilloi , new species, and R. brevicauda , new species, somewhat resembles that of R. spinifrons from Borneo. However, in both R. bendanilloi and R. brevicauda , the paramere is strongly constricted at the distal third (while in R. spinifrons , it is constricted at distal half) and the apical hook of the paramere is evenly thick throughout its length (in R. spinifrons , it is tapering towards its narrowly rounded tip).

There are also substantial differences between R. spinifrons and all five Philippine species of the R. gracilis group ( R. stali , R. bisaya , R. bendanilloi , R. brevicauda , and R. pangantihoni ). Ranatra spinifrons has a longer siphon (about two-thirds of body length and clearly longer than the abdomen), a more prominent tubercle on its vertex (its height greater than eye width in lateral view), a simple lorum without a tubercle, and a longer finger-like projection on the second antennal segment (about two-thirds to three quarters of the length of the third antennal segment). In addition, the female of R. spinifrons has the midline of sternum VI almost straight in lateral view, and a shorter operculum (surpassing the apex of connexivum of about one fifth the length of operculum). In contrast, Ranatra stali and its related species from the Philippines have a much shorter respiratory siphon (clearly shorter than the abdomen, only slightly longer than sterna IV–V combined), a lower tubercle on the vertex (with height about half eye width in lateral view), a more swollen lorum with a small, but distinct dorsal tubercle, and a shorter finger-like projection on the second antennal segment (about 0.2–0.4× the length of the third segment). Female specimens of these five species have the posterior half of sternum VI distinctly raised in lateral view, and a longer operculum (surpassing the apex of connexivum of about one third the length of operculum).

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. 7. Ranatra pangantihoni, 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, operculum. (B, C same scale; D, E same scale; F, G same scale).

Fig. 8. Parameres of Ranatra pangantihoni, new species, of specimens from various localities. A–C, from Nueva Viscaya; D–F, from Ilocos; G–I, from Laguna (Mount Makiling); J–L, from Laguna (Tampalit Falls); M–O, from Romblon. A, D, G, J, M, lateral view; B, E, H, K, N, apical part, sub-caudal view; C, F, I, L, O, apical part, inner view (all of same scale).