Rhacophorus rhyssocephalus Wolf, 1936

Herlambang, Alamsyah Elang Nusa, Sabinhaliduna, Efendi, Trilaksono, Wahyu, Anita, Syahfitri, Riyanto, Awal, Hamidy, Amir, Krone, Isaac, Amini, Sina, Méndez, María José Navarrete, Herr, Mark & Mcguire, Jimmy A., 2025, Taxonomic Reassessment of an Enigmatic Flying Frog (Amphibia: Rhacophoridae) from Sangihe Island, Indonesia, Zootaxa 5636 (1), pp. 121-143 : 128-132

Rhacophorus rhyssocephalus Wolf, 1936

urn:lsid:zoobank.org:act:077AFB25-B249-4473-9C17-D3E76F557FC5

Neotype. MZB Amph 33593 ( Figure 4B, 4E , 5 ), an adult female collected on 5 August 2023, from Sahendaruman Mountain , Ulungpeliang , Kecamatan Tamako, Kabupaten Kepulauan Sangihe, North Sulawesi, Indonesia (03 o 30.887’N, 125 o 32.487E; 446 masl) by Efendi Sabinhaliduna, Wahyu Trilaksono, Syahfitri Anita, Isaac Krone, Sina Amini, María José Navarrete Méndez, Mark Herr, Jimmy McGuire.

Isoneotype. MZB Amph 33594 from the same locality as the neotype collected by Rio Jimmi Kapona and Muhammad Abdi. Locality and collection time are the same as for the neotype .

Diagnosis. We assign R. rhyssocephalus to the genus Rhacophorus and not Leptomantis based on the following characters: large body size; dermal folds along limbs present; supercloacal fold present ( Jiang et al. 2019). R. rhyssocephalus can be distinguished from its congeners by having several conspicuous bony ridges on the dorsal surface of its head; a ridge with a granular structure above each tympanum and a U-shaped bony ridge filled with coarse bony grains running along the medial orbital margins and joining posteriorly in the parietal region ( Figure 4E ).

Description of Neotype. An adult female ( Figure 4B ); SVL 86.7 mm; head depressed, and slightly longer (HL/SVL= 0.36) than wide (HW/SVL= 0.35); snout rounded in lateral view, projecting beyond mandible, longer (SL/SVL = 0.18) than eye diameter (ED/SVL = 0.11); canthus rostralis rounded and clearly curved; loreal region concave; nostril oval and slightly protuberant, without flap of skin, positioned vertically, closer to tip of snout than to eye (EN/SL = 0.59); internarial distance (IND/SVL =0.08) about slightly less than half of interorbital distance (IOD/SVL = 0.13); eyes relatively large (ED/SVL = 0.11), protuberant, pupil horizontally elliptical, twice as large as tympanum diameter (TD/SVL = 0.05); circular, distinct tympanum, three times the distance between the eye and the tympanum distance (ETD/SVL = 0.02); well-developed rows of vomerine teeth; choana oval shaped; tongue notched posteriorly; vocal sac and vocal slit absent.

Forelimbs slender, relatively robust, forearm length is shorter than hand length (FLL/HAL = 0.75), and about one-fifth the length of the SVL (FLL/SVL= 0.21); a small, rounded inner palmar tubercle (IPTL/SVL= 0.07), about a quarter of third finger length (Fin3L/SVL= 0.26), outer one absent; finger length formula I <II <IV <III; tips of all fingers expanded into large disks with circum-marginal grooves; disk of third finger (Fin3DW/SVL=0.08) wider than tympanum diameter (Fin3DW/TD= 1.43); fingers almost full webbed; webbing formula I 1½-1½ II 1-1 III 1-1 IV ( Figure 5D ); subarticular tubercles rounded, formula 1, 1, 2, 2.

Hindlimbs relatively long, slender, tibiotarsal articulation extends to the posterior of nostril when fully stretched leg adpressed to body; thigh (THL/SVL= 0.45) shorter than tibia (TL/SVL= 0.55), and almost the same as foot length(FL/SVL= 0.44); relative length of toes I<II<V<III<IV; tips of toes expanded into round disks with distinct circum-marginal grooves; disk of fourth toe is smaller than disk of third finger (Toe4DW/Fin3DW= 0.61); toes fully webbed, toe webbing formula I 0-0 II 0-0 III 0-0 IV 0-0 V ( Figure 5E ); subarticular tubercles distinct, rounded, formula 1, 1, 2, 3, 2; present of wrinkled skin fold on lateral side of outer fifth toe and tarsus.

Dorsum nearly smooth, scattered with non-spinose tubercles; flanks wrinkled; underside of chin and chest smooth, abdomen and thighs coarsely granular; the granulation much denser in the cloacal region; outer margin of hand, forearm, foot, and heel with low wrinkled skin folds; the dermal ridges reach the tibiotarsal articulation and form a pointed projection; very low supra-cloacal dermal ridges present; several conspicuous bony ridges with granular structure above the tympanum, and a U-shaped bony ridge filled with coarse bony grains on the interorbital area of the head.

Coloration. Coloration in life is medium brown on the dorsum with indistinct and irregular dark dots and spots; distinct yellow dots and black spots scattered on the back, head, and limbs, with yellow spots appearing green where they overlap the indistinct dark spots; yellow with dark spots on the dorsolateral background; dorsal part of the fingers and toes with dark dots and yellow spots; tips of the fingers and toes pale brown dorsally, and webbing dark brown; ventral part of the forearm, hand, foot, tarsus, and lower body whitish; anterior part of the ventral body and chin slightly yellow; pupil horizontal with the iris yellowish brown; sclera (orbital arc) dark in color. Lateral skin fold bright yellow; dermal ridge on the heels dark brown; supra-cloacal dermal ridges white. In alcohol, dorsal color fades to dark brown; some of the yellow dots and spots turn pale purple.

Variation. Individuals of the type series are morphologically similar, although the isoneotype has a smaller body size than the neotype ( Table 5 ). The coloration of the isoneotype is the same as for the neotype.

Etymology. We elevate Wolf’s (1936) proposed subspecies name to full species status. Rhyssocephalus is derived from Greek, with ‘ Rhysso ’ means ‘wrinkled’ and ‘ Cephalus ’ means ‘head’. We suggest the English common name “Sangir Flying-frog”. We suggest the Indonesian name “Katak-terbang Sangir.”

Comparisons. Rhacophorus rhyssocephalus is distinguished from R. pardalis ( Figure 4A, 4D ), R. georgii ( Figure 4C, 4F ), and other known flying frogs ( Rhacophorus spp. , Leptomantis spp. , and Zhangixalus spp. ) by the presence of distinct, low bony ridges filled with coarse bony grains on the dorsum of the head. There is one ridge above each tympanum and one U-shaped ridge that runs along the medial orbital margins to join medially in the parietal region. We used the data we have as a basis for creating an identification key for Rhacophorus endemic to Sulawesi and its surrounding small islands.

Figures

FIGURE 4. A. Live specimen of R. pardalis from eastern Borneo (MZB Amph 16355). B. Live specimen of R. rhyssocephalus from Sangihe (MZB Amph 33593). C. Live specimen of R. georgii from Central Sulawesi (Uncollected), photographed by Rocky RT Lembah. D. Dorsal view of the head of R. pardalis (MZB Amph 16355). E. R. rhyssocephalus (MZB Amph 33593). F. R. georgii (MZB Amph 23395). The yellow arrow represents key characteristics of R. rhyssocephalus and R. georgii.

FIGURE 5. A. Dorsal, B. Ventral, C. Lateral view of the head, D. Ventral view of right hand, and E. Ventral view of left foot of the neotype R. rhyssocephalus (MZB Amph 33593). Scale = 10 mm.