Pristimantis imthurni, Kok, 2013

Kok, Philippe J. R., 2013, Two new charismatic Pristimantis species (Anura: Craugastoridae) from the tepuis of “ The Lost World ” (Pantepui region, South America), European Journal of Taxonomy 60, pp. 1-24 : 15-21

Pristimantis imthurni sp. nov.

Figs 8-10 , Table 1

urn:lsid:zoobank.org:act:9AFC18C4-23A0-4C20-96EB-480F0F512791

Eleutherodactylus sp. H – McDiarmid & Donnelly 2005: 514 [table 18A.1], 521.

Definition and diagnosis

A small species of the genus Pristimantis currently not assigned to any species group, but morphologically most similar to species of the polyphyletic unistrigatus species group (sensu Hedges et al. 2008, see also discussion in Kok et al. 2011) mainly characterized in having Finger I shorter than II, Toe V longer than III, extending to the distal edge of the distal subarticular tubercle of Toe IV when toes are adpressed, and by the absence of cranial crests and the presence of vomerine teeth. The new species is characterized by the following unique combination of characters: (1) body small, male 22.9 mm SVL; (2) dorsal skin smooth, belly skin coarsely areolate; (3) tympanum absent (tympanic membrane not differentiated and tympanic annulus not visible externally); (4) tiny pharyngeal ostia present; (5) snout broadly rounded in dorsal view and in profile, canthus rostralis nearly straight in dorsal view, rounded in cross section, loreal region concave, flaring slightly at upper lip; (6) upper eyelid smooth with one barely distinct enlarged tubercle; (7) choanae very small, round, dentigerous processes of vomers inconspicuous, ovoid, posterior and medial to choanae, each bearing 3-4 teeth; (8) absence of vocal slits in male; (9) tongue cordiform; (10) two large, broadly connected, mostly unpigmented nuptial pads on each thumb in male; (11) Finger I shorter than II; (12) fingers with lateral fringes, best developed preaxially on Fingers II-III; (13) ulnar tubercles absent; (14) tarsal tubercles absent, one inconspicuous calcar tubercle present; (15) inner metatarsal tubercle oval, about four times the size of the round, projecting outer metatarsal tubercle; (16) Toe V longer than III, extending to the distal edge of the distal tubercle on Toe IV when toes are adpressed; (17) toes with lateral fringes, best developed preaxially on Toes III-IV, webbing basal between Toes IV-V; (18) in life dorsal background colouration is vivid yellow with a chocolate brown middorsal stripe and chocolate brown flanks, ventral colouration is translucent brown with a few white spots and flecks; (19) in preservative dorsal background colouration is pale yellow with a light brown middorsal stripe and light brown flanks, ventral colouration is light grey with a few white spots and flecks.

Etymology

The specific epithet is a noun in the genitive case, honouring Sir Everard F. im Thurn (1852-1932), British colonial official, author, explorer, botanist, and photographer. Everard im Thurn was the first to climb a major tepui (Mount Roraima in December 1884), along with British surveyor Harry Perkins, a Pomeroon Amerindian named Gabriel, and five other unnamed Amerindians ( Dalziell 2007). Im Thurn’s expedition on Roraima and his numerous discoveries were partly eclipsed by the popular novel that they inspired: “The Lost World” by Sir Arthur Conan Doyle (see Introduction; Dalziell 2007).

Material examined

Holotype

VENEZUELA: an adult male collected by Philippe J. R. Kok, 20 Jun. 2012 at 20h37, summit of Ptaritepui , Bolívar state, 5°46’09” N, 61°49’02” W, 2471 m elevation, IRSNB 4165 (field number PK 3671).

Morphological comparisons with congeneric species

For the same reasons mentioned above, comparisons with congeners only focus on the 21 Pristimantis species known to occur in the Pantepui region.

Pristimantis imthurni sp. nov. is most easily distinguished from P. abakapa , P. aureoventris , P. avius , P. cantitans , P. dendrobatoides , P. guaiquinimensis , P. marmoratus , P. memorans , P. pruinatus , P. pulvinatus , P. saltissimus , P. sarisarinama , P. vilarsi , P. yuruaniensis , and P. zeuctotylus by lacking a differentiated tympanic membrane and an external tympanic annulus (at least one of these structures is detectable in the latter 15 species). It further differs from P. vilarsi and P. zeuctotylus in having Finger I <II (Finger I> II in P. vilarsi and P. zeuctotylus ).

Pristimantis imthurni sp. nov. is immediately distinguished from P. auricarens , P. jester , P. marahuaka , P. muchimuk , and P. yaviensis in having lateral fringes on most fingers and toes (absent or limited to a weak keel in the latter 5 species).

By lacking a differentiated tympanic membrane and an external tympanic annulus, and in having lateral fringes on fingers and toes, Pristimantis imthurni sp. nov. is morphologically most similar to P. jamescameroni sp. nov., described earlier in this paper. These two species are mainly distinguished based on distinct dorsal and ventral colour patterns (compare Fig. 2 with Fig. 8 ), skin texture (smooth in P. imthurni sp. nov. vs. shagreen in P. jamescameroni sp. nov.), condition of the supratympanic fold (inconspicuous in P. imthurni sp. nov. vs. conspicuous in P. jamescameroni sp. nov.), and head proportion (shorter, with a more rounded snout in P. imthurni sp. nov.). Besides being morphologically reliably diagnosable, the two species are currently geographically isolated (isolated lineage segments).

Description of the holotype

An adult male 22.9 mm SVL ( Figs 8-10 , see Table 1 for measurements), in very good condition, except a large scar under the right thigh where a piece of muscle was removed prior to preservation. Head slightly longer than wide (HW 97.7% of HL), wider than body; HW 37.1% of SVL; HL 38.0% of SVL; cranial crests absent. Snout longer than eye length (SL 112.1% of EL), broadly rounded in dorsal view and in profile; canthus rostralis nearly straight in dorsal view, rounded in cross section, loreal region concave, flaring slightly at upper lip; eye-naris distance shorter than eye length (EN 72.7% of EL). Nares slightly protuberant, directed posterolaterally, visible in frontal and dorsal views. Widest upper eyelid width narrower than interorbital distance (upper eyelid width 81.5% of IO), upper eyelid smooth with one barely visible enlarged tubercle on each eyelid. Tympanum absent (tympanic membrane not differentiated and tympanic annulus not visible externally); tiny pharyngeal ostia present. Supratympanic fold inconspicuous in life, barely visible and fragmented in preservative, slightly arched, apparently originating at posterior corner of eye, failing to reach shoulder; a few low and small post-rictal tubercles. Choanae very small, round; dentigerous processes of vomers inconspicuous, ovoid, posterior and medial to choanae, each bearing 3-4 teeth. Tongue cordiform, slightly wider than long, rounded posteriorly, posterior one-third free. Vocal slits and vocal sac absent.

Dorsal skin smooth, including on head; middorsal raphe barely detectable in preservative, well visible in life; no dermal folds or ridges visible on dorsal surface; flanks slightly granular. Throat and upper chest surfaces smooth; no thoracic fold detectable; belly skin coarsely areolate; no discoidal fold detectable; posteroventral thigh and cloacal region coarsely areolate; cloacal sheath absent, two distinctly enlarged tubercles below cloaca.

Hand length 27.1% of SVL. Finger I 88.6% of II. Relative length of fingers III> IV> II> I; adpressed Finger I fails to reach proximal edge of digital pad of Finger II; adpressed Finger IV reaches proximal edge of digital pad of Finger III. Two large, broadly connected, non-spinous, mostly unpigmented (translucent when wet, white when dry) nuptial pads on each thumb, extending from the preaxial surface of the thenar tubercle and invading most of it, along the dorsal and the preaxial surface of the thumb. Lateral fringes on all fingers, best developed preaxially on Fingers II-III ( Fig. 9 ). Finger discs expanded, elliptical, broader than long, circumferential groove conspicuous, distal edge of disc rounded; disc of Finger III 1.8 times wider that the distal end of the adjacent phalanx. Palmar tubercle large, well defined, fully pigmented, deeply bifid; thenar tubercle large, protuberant, ovoid; supernumerary tubercles few, of variable sizes, slightly protuberant; subarticular tubercles large, round and protuberant, one each on FI and FII, two each on FIII and FIV. Ulnar tubercles absent; presence of a small antebrachial tubercle.

Hind limbs moderate in length, heels slightly overlap when held at right angles to sagittal plane; TIL 50.2% of SVL; FL 40.6% of SVL. Relative length of Toes IV> V> III> II> I; tip of Toe V extends to the distal edge of the distal subarticular tubercle on Toe IV; tip of Toe III extends to the distal edge of the penultimate subarticular tubercle on Toe IV. Lateral fringes on all toes, best developed preaxially on Toes III-IV ( Fig. 9 ); webbing basal between Toe IV-V. Toe discs slightly larger in size than finger discs, WTD/WFD = 1.08; toe discs expanded, elliptical, broader than long, circumferential groove conspicuous, distal edge of disc rounded. Inner metatarsal tubercle elongate, oval, about four times the size of the projecting, round outer metatarsal tubercle; subarticular tubercles round, large and protuberant; supernumerary plantar tubercles small, low and round, increasing in size distally. Single, inconspicuous, very small, round calcar tubercle; no outer tarsal tubercles detectable; inner tarsal fold not detectable.

Colour of holotype in life (see Fig. 8 )

Dorsal background colouration vivid yellow, top of head greyish brown; chocolate brown middorsal stripe and chocolate brown band on flanks; ill-defined, irregular reddish orange dorsolateral line; a few reddish orange blotches on the posterior part of the dorsum; a few reddish orange minute speckles on flanks; brown facemask; enlarged tubercle on eyelid whitish. Lower flanks yellow; groins, anterior thighs, and armpits brown. Arms and legs greyish brown with a few ill-defined white and dark yellow blotches. Ventral surfaces translucent greyish brown with a few irregular white spots and flecks; posterior surface of thighs and cloacal area brown. Upper face of hands and feet greyish brown with a few white and yellow markings; upper face of tip of fingers white; upper face of tip of Toes I-III white, brown on Toes IV-V. Palms, soles, undersurface of fingers and toes brown; discs greyish brown. Iris silver with dark brown venation and an ill-defined broad horizontal brownish stripe.

Colour of Holotype in preservative (see Fig. 10 )

After 13 months in 70% ethanol (July 2013). Vivid yellow faded to pale yellow. Chocolate brown and brown faded to light brown; top of head is dark brown; ill-defined white and dark yellow blotches on arms and legs are slightly more conspicuous and form irregular, ill-defined transverse bands; dorsal pattern turned generally more conspicuous. Ventral colouration is light grey with a few white spots and flecks. Granules in the cloacal area, as well as subarticular and supernumerary tubercles became dark brown. Discs are grey.

Distribution and ecology

Pristimantis imthurni sp. nov. is only known from the summit of Ptari-tepui ( Figs 1B , 6B , 11 ), Bolívar state, Venezuela, where it occurs at 2471 m elevation. Ptari-tepui lies in the Ptari massif, in the Los Testigos subdistrict ( McDiarmid & Donnelly 2005). It is located ca. 47 km NE of the Chimantá massif, and ca. 22 km SE of Kamarkawarai-tepui (airline). According to the GPS, Ptari-tepui reaches a maximal elevation of about 2471 m above sea level. The summit area of Ptari-tepui is ca. 1 km 2 and is dominated by flat open rock surfaces and small islands of low meadow-like tepui vegetation ( Huber 1995; Fig. 11B ).

The male holotype – and single specimen collected – was found at night while calling partly concealed in the muddy soil in a small vegetation patch. A few other males were heard calling very sporadically from other small vegetation islands by day or night, but could not be located. Pristimantis imthurni sp. nov.

is not abundant. The only other anuran reported from the summit of Ptari-tepui is Tepuihyla rimarum Ayarzagüena, Señaris & Gorzula, 1993 , which apparently also occurs in low density (pers. obs.).

Figures

Fig. 8. Pristimantis imthurni sp. nov. in life. A. Dorsolateral view of the ♂ holotype (IRSNB 4165). B. Ventral view of the same specimen. Photographs by the author.

Fig. 9. Pristimantis imthurni sp. nov. Ventral view of left hand and left foot of the ♂ holotype (IRSNB 4165). Photographs by the author.

Fig. 10. Pristimantis imthurni sp. nov. in preservative. A. Dorsol view of the ♂ holotype (IRSNB 4165). B. Ventral view of the same specimen. Photographs by the author.

Fig. 2. Pristimantis jamescameroni sp. nov. Intraspecific variation in dorsal and ventral colour pattern in living specimens. A. Dorsolateral view of the ♂ holotype (IRSNB 4160). B. Ventral view of the same specimen. C. Dorsolateral view of a ♀ paratype (IRSNB 4163). D. Ventral view of the same specimen. E. Dorsolateral view of a ♀ paratype (IRSNB 4162). F. Ventral view of the same specimen. Photographs by the author.

Fig. 1. A. Map of the Pantepui region, located in the western part of the Guiana Shield. The white rectangle corresponds to the area enlarged in (B). B. Distribution of known tepui summit Pristimantis species occurring east of the Rio Caroní in Venezuela and in western Guyana: P. aureoventris (Wei- Assipu-tepui and upper slopes of Mount Roraima), P. yuruaniensis (Yuruaní-tepui), P. muchimuk (Churí-tepui), P. abakapa (Abakapá-tepui), P. auricarens and P. pulvinatus (Auyán-tepui); (1) Apradatepui, type locality of Pristimantis jamescameroni sp. nov. (area enlarged in Fig. 6A); (2) Ptari-tepui, type locality of Pristimantis imthurni sp. nov. (area enlarged in Fig. 6B).

Fig. 6. A. Satellite map of the Aprada massif, showing the location of Aprada-tepui and neighbouring smaller table mountains. Yellow star indicates the type locality of Pristimantis jamescameroni. B. Satellite map of the Ptari massif, showing the location of Ptari-tepui and neighbouring mountains. Yellow star indicates the type locality of Pristimantis imthurni. Satellite maps © Google Maps.

Fig. 11. A. Ptari-tepui, photographed from the surrounding savannah looking to the NE (21 Jun. 2012). B. Summit of Ptari-tepui (21 Jun. 2012). Photographs by the author.