Riolama inopinata, Kok, 2015

Kok, Philippe J. R., 2015, A new species of the Pantepui endemic genus Riolama (Squamata: Gymnophthalmidae) from the summit of Murisipán-tepui, with the erection of a new gymnophthalmid subfamily, Zoological Journal of the Linnean Society 174 (3), pp. 500-518 : 506-513

RIOLAMA INOPINATA SP. NOV.

( FIGS 3–7 ; TABLE 3)

Holotype

IRSNB 2679 (field number PK 3660 , Fig. 3A, C ), a male collected by Philippe J. R. Kok, 19 June 2012 at 11:00 h, summit of Murisipán-tepui , Bolívar State, Venezuela (5°52′08″N, 62°04′28″W; 2400 m a.s.l.).

Paratype

One male ( IRSNB 2680 , field number PK 3558, Fig. 3B ) collected by Philippe J. R. Kok, 19 June 2012 at 08:45 h, summit of Murisipán-tepui , Bolívar State, Venezuela (5°52′10″N, 62°04′31″W; 2413 m a.s.l.) .

Etymology

The specific name, meaning ‘unexpected’ in Latin, is considered a noun in apposition and refers to the unforeseen discovery of a Riolama species on a tepui from the Los Testigos Massif.

Generic allocation

The new species clearly belongs to the genus Riolama , fitting the main diagnostic traits for the genus proposed by Uzzell (1973): (1) head scales without striations or rugosities; (2) single frontonasal and frontal; (3) dorsal scales hexagonal, uniformly keeled; (4) tympanum heavily pigmented and feebly recessed; (5) digits depressed with swollen tips; and (6) oblique plicae rather than papillae on the anterior and posterior surfaces of the tongue. The new species also lacks a claw on the first finger, a synapomorphy for the genus that was apparently missed by Boulenger (1900) and Uzzell (1973), but was highlighted by Myers & Donnelly (2001). Generic allocation was also confirmed by molecular phylogenetic analyses (see below).

Definition and diagnosis

In addition to the generic diagnostic features, the new species is characterized by the following unique combination of characters: (1) size small, body slender (maximum known SVL 42.8 mm), neck short (15.4– 15.5% of SVL); (2) tail slightly greater than twice as long as body; (3) mid-dorsal scales in 30 or 31 transverse rows; (4) ventral scales in 18 or 19 transverse rows; (5) scales around midbody, 28; (6) seven supralabials; (7) five or six infralabials; (8) subdigital lamellae divided in small granular scales; (9) anal plate with four or five scales; (10) femoral pores small, poorly swollen, ten or 11 in males; (11) oblique chevron- shaped plicae covering the dorsal surface of tongue interrupted by a small midsection of imbricate scalelike papillae; (12) hemipenis small, globose, weakly bilobed, sulcus spermaticus flanked by an extensive nude area on each side, apical structure nude, asulcate, and lateral faces of organ with short series of small roughly equidistant feebly developed flounces, each bearing a single medial hook-shaped spine.

Riolama inopinata sp. nov. is immediately distinguished from R. leucosticta , R. luridiventris , and R. uzzelli – the only described species in the genus – by its subdigital lamellae divided in small granular scales (undivided in the aforementioned species, only rarely basally divided in R. leucosticta ; for comparison, see Fig. 4 ). Riolama inopinata sp. nov. further differs from R. leucosticta in having: (1) more, smaller, and less swollen femoral pores in males (ten or 11 versus seven to nine in R. leucosticta , see Fig. 5A, B for comparison); (2) more infralabials (five or six versus three or four in R. leucosticta ); (3) the last supralabial more than twice as long as the one before it (subequal in R. leucosticta ); (4) a shorter neck (15.4–15.5% of SVL versus 15.8–19.3% of SVL in R. leucosticta ); (5) keels on dorsal scales distinctly less pronounced; (6) one row of lateral scales per dorsal scale till mid-flank (usually two rows of lateral scales per dorsal scale on flank in R. leucosticta , see Fig. 5C, D ); and (7) slightly deeper auditory meatus. Riolama inopinata sp. nov. further differs from R. luridiventris and R. uzzelli in having: (1) fewer femoral pores in males (ten or 11 versus 14– 17 in R. luridiventris and 13–15 in R. uzzelli ); (2) fewer scales around midbody (28 versus 36–39 in R. luridiventris and 34 in R. uzzelli ); (3) fewer anal scales (four or five versus ten or 11 in R. luridiventris and nine or ten in R. uzzelli ); (4) ventral surfaces of body and hindlimbs black with scattered pale spots in preservative (brown to dark brown without well-defined spots in R. luridiventris and R. uzzelli ); and (5) chevronshaped plicae interrupted by a midsection of imbricate scale-like papillae on the dorsal surface of the tongue (tongue reported as completely covered by chevron-shaped plicae in R. luridiventris and R. uzzelli ).

Description of the holotype

A male ( Fig. 3A, C ) in good condition, except for a small longitudinal ventral incision, a piece of tissue liver excised, and the translucent epidermal layer that covers dorsal surface of scales lost on most dorsal scales. The holotype is 41.9 mm SVL and 86.8 mm TL (tip regenerated on ∼17.0 mm; see also Table 3). Limbs moderately long, digits overlapping when limbs are adpressed along body. Snout acuminate. HL 23% of SVL, 1.4 times longer than wide, 1.5 times wider than high; head slightly wider than neck. Neck long, 67% of HL, 32% of AXG. SAL 91% of AXG, 44% of SVL. Body wider than deep. Tail slightly laterally flattened, about 2.1 times longer than SVL. Limbs pentadactyl with all digits clawed, except on finger I. Forelimb ∼29% of SVL, 60% of AXG; hindlimb ∼41% of SVL, 84% of AXG.

Scutellation on the dorsal surface of head is typical for the genus ( Uzzell, 1973: fig. 24), lacking a triangular interprefrontal scale as reported in R. uzzelli ( Molina & Señaris, 2003) ; all head scales intact. Head scales smooth with a few minute scattered pits, with pits being mostly concentrated on the margins of scales, but covering the entire surface of the rostral and the frontonasal.

Rostral much wider than deep, laterally in contact with nasal and first supralabial, dorsally in contact with large frontonasal. Frontonasal with nearly straight anterior margin, posteriorly rounded. Paired prefrontals in contact, medial suture short. Frontal wider anteriorly, with an almost straight anterior margin. Paired frontoparietals with long medial suture, in contact with interparietal, parietals, and two posterior supraoculars, in point contact with third supraocular on the right side. Four supraoculars: three large and subequal in size; one smaller located anteriorly. Interparietal posteriorly rounded. Parietals slightly wider than interparietal, not extending as far as interparietal posteriorly. A series of seven small to large occipitals (postparietals) circling the common posterior margin of parietals and interparietal, the lateral ones being the largest ( Fig. 6 ).

Nasal scale entire, with a minute indentation situated posterodorsally to nostril on both sides. Nasal scale in contact with rostral, posteriorly in short contact with prefrontal, in contact with a small loreal on the left side, with a frenocular on the right side. Loreal fused with nasal on the right side, small loreal on the left side, rectangular, higher than wide, in broad contact with presuperciliary and frenocular. One very small preocular, two large postoculars. First superciliary large, preceded by a presuperciliary about two-thirds the size of first superciliary, followed by five superciliaries, the second and the sixth being higher than wide. No small azygous scale between superciliaries and supraoculars. Frenocular followed posteriorly by five suboculars. Third and fourth suboculars slightly extending to lip between supralabials 4 or 5 and 5 or 6, respectively. Suboculars separated from palpebrals by three or four poorly defined rows of mostly inconspicuous tiny scales, two of them distinctly enlarged with angular downward protrusion between suboculars. Seven supralabials, last one much larger, more than twice as long as the sixth supralabial ( Fig. 6 ).

Eight ciliaries along upper eyelid; two medial short rows of a few tiny scales between ciliaries and supraciliaries. Lower eyelid scales opaque, heavily pigmented, with four slightly higher than wide palpebrals ( Fig. 6 ).

Temporal scales subimbricate, smooth, with slightly domed surfaces, distinctly larger above and smaller below. Ear opening broad, ovoid, slightly inclined posterodorsally, edged with small, slightly pebblelike scales; tympanum recessed, pigmented, ‘scalelike’ ( Fig. 6 ).

Underside of head with five infralabials on each side. A large mental followed by a large postmental in contact with first two infralabials. Three pairs of large genials, first two pairs in broad contact medially, in lateral contact with infralabials 2–5, third pair medially separated by a small scale, in contact with infralabial 5 only; one pair of large postgenials, in short contact medially, each scale widely separated from infralabials by one scale. Gulars arranged in seven transverse rows (including collar), becoming progressively larger posteriad, and culminating in a well-defined collar row of eight scales, the three median scales being the largest; gulars not in distinct longitudinal rows. Side of neck between ear and collar with subequal, subimbricate, and irregularly shaped, slightly pebble-like scales ( Fig. 6 ).

Middorsal scales 30. Dorsal scales on neck imbricate, irregularly shaped, the mid-dorsal scales keeled, the lateral scales smooth. Dorsal body scales large, parallel-sided, hexagonal and longer than wide, keeled and mucronate, in transverse rows only. Lateral scales on upper flank keeled, similar to dorsals, becoming distinctly smaller and smooth on lower flank, progressively much smaller, juxtaposed and pebble-like towards axilla and groin ( Fig. 5C ).

Ventral scales distinctly wider than dorsals and laterals, smooth, juxtaposed, quadrangular, slightly longer than wide; in six longitudinal rows at midbody and 18 transverse rows between collar and anal plates ( Fig. 3C ).

Anal plate with five scales: two large marginal scales similar in shape and size, three preanal scales, with the middle scale much larger than the outer scales ( Fig. 5A ). Femoral pores small, poorly swollen, located either in a single scale or in the middle of three scales, mostly in linear contact; 11 pores on left thigh, ten on right. Pores do not extend onto anal scales strictly speaking, but one on each side is in the preanal position ( Fig. 5A ).

Caudal scales in transverse rows around tail, dorsally similar to dorsal body scales (but smaller in size), longer than wide, keeled, imbricate, mucronate; caudal scales smooth laterally and ventrally, two midventral longitudinal rows extend from vent to tip of tail.

Scales on dorsal surfaces of arm large, smooth, imbricate; ventral surfaces of arm with similar, but smaller scales, much smaller and less imbricate on ventral face of upper arm. Hindlimbs with large, smooth to feebly keeled subimbricate to imbricate scales on anterior face of thighs and on lower legs; scales similar, but never keeled, on ventral side of thigh. Dorsal and posterior sides of thigh with much smaller, irregularly shaped juxtaposed scales.

Large, smooth, imbricate scales atop hands and feet, some feebly keeled on the posterior side of feet. SAF, scales atop finger IV; other abbreviations are defined in the text.

*Tail regenerated.

†Data corresponding to right/left side.

Supradigital scales single; upper and lower ungualsheath scales covering base of claws, leaving tips well exposed; claw missing on first finger. Palms and soles covered with small slightly raised juxtaposed scales ( Fig. 4A, B ). Two enlarged smooth thenar scales at base of pollex, the proximal one with a slightly protruding keel on the inner edge; a similar but smaller pair of enlarged scales at base of first toe. Most subdigital lamellae divided in two, sometimes in three slightly raised juxtaposed scales ( Fig. 4A, B ). Lamellae under first (I) through fifth (V) finger (right/left side): I, 5/4; II, 8/9; III, 12/11; IV, 13/13; V, 8/7. Lamellae under first (I) through fifth (V) toe (right/left side): I, 7/6; II, 11/ 10; III, 15/13; IV, 20/19; V, 11/12. Note: because of the peculiar state of the subdigital lamellae, distinction between the proximal lamellae and the scales covering palms and soles is difficult and somewhat arbitrary.

Tongue lanceolate; proximal third unpigmented, distal two-thirds progressively more pigmented until fork, which is heavily pigmented. Entire upper surface behind fork covered with oblique chevron-shaped plicae, except medially immediately after a distal shallow mediodorsal groove, where a small area of imbricate scale-like pa- pillae is found. Raised medioventral side of tongue with numerous (about ten) minute, oblique, anteriorly converging infralingual plicae, with blunt free edges that alternate from side to side (appearance most similar to the condition illustrated for Prionodactylus by Harris, 1985: 562, fig. 2a); anterior pair of plicae feebly swollen, bluntly pointed and much larger than those following. Shallow medioventral groove.

Anterior maxillary and dentary teeth conical, unicuspid, with no or very feeble recurvature, becoming larger posteriorly.

Colour of holotype in life

Dorsum chestnut brown with two conspicuous orangebrown dorsolateral stripes – about one dorsal scale wide – extending from behind the temporal scales and gradually fading to the tip of the tail, where it is not visible anymore ( Fig. 3A ). Dorsolateral stripes bordered dorsally and ventrally by narrow bluish black lines on body and proximal part of the tail. Top of head chestnut brown with no particular marking. Sides of head, sides of tail, flanks, arms and legs, including digits, and ventral surfaces of forelimbs greyish brown speckled with dark brown. Rear of thighs dark brown. Underside of head and throat pale golden grey, with a few scattered irregular small black markings. Ventral surfaces of body and hindlimbs shiny black with scattered pale golden grey spots (usually one or two spots per ventral scale, Fig. 3C ). Dorsal surface of tail pale brown. Ventral surface of tail pale golden grey, with scattered small irregular black markings. Palms and soles dark brown. Tympanum dark brown. Iris orangebrown; as in other Riolama species , pupil is not circular, but slightly ‘sphincter-shaped’ (i.e. with radial rays coming out from the centre).

Colour of holotype in preservative

After 24 months in 70% ethanol the colours are generally faded. Dorsolateral stripes are pale brown, lines bordering dorsolateral stripes are black, lateral side of body is dark brown, ventral surface of body is black with white spots, underside of head, throat, and ventral surface of tail are white with scattered irregular small dark-brown markings. When the translucent epidermal layer is lost scales appear pale grey ( Fig. 7 ).

Variation in paratype

Very little variation is found between the holotype and the paratype ( Table 3). Like the holotype, the paratype has subdigital lamellae divided in small granular scales, and seven supralabials, the last one being more than twice as long as the sixth supralabial. Colour in life and preservative is also very similar ( Figs 3 , 7A, B ). Unlike the holotype, the paratype has posterior margin of interparietal in contact with median occipital slightly concave (convex in the holotype, posterior margin of interparietal rounded), one small azygous scale between superciliaries and third supraocular on both sides (absent in the holotype), pair of large postgenials separated by a small scale (in short contact medially in the holotype), and five slightly higher than wide palpebrals (four in the holotype).

Hemipenial morphology

Hemipenial body very small ( Figs 5A , 7C, D ; see Discussion), extending less than three subcaudal rows when adpressed to the tail in both holotype and paratype. Right hemipenis of holotype about 2.5 mm in length and 1.8 mm across its widest point (fully everted but not maximally expanded), right hemipenis of paratype about 2.5 mm in length and 2.0 mm across its widest point (fully everted and maximally expanded, but slightly damaged during preparation). Hemipenial body globose, tapered near the base, weakly and symmetrically bilobed. Sulcus spermaticus simple and straight, very shallow, running medially towards the lobes, slightly broader near crotch. Sulcus flanked by an extensive nude area on each side. Apical structure nude, absence of complex folding on apices of lobes. Base of hemipenis nude, absence of any medioproximal asulcate flounces (sensu Myers et al., 2009). Asulcate and lateral faces of organ with short series of small roughly equidistant feebly developed flounces (best detectable at high magnification) on each side, each flounce bearing a single medial hook-shaped spine. About 16–21 of these small flounces bearing hook-shaped spines, most projecting towards the base of organ, arranged in a semicircular shape on each side of organ ( Fig. 7D ).

Distribution and ecology

Riolama inopinata sp. nov. is currently only known from around 2400 m a.s.l. on the summit of Murisipántepui, a small tepui located in the Los Testigos Massif, Bolívar State, Venezuela ( Figs 1 , 2 ). The Los Testigos Massif lies north to the Chimantá Massif, between Auyán-tepui to the west and Ptari-tepui to the east ( Fig. 1B ). Most of the very summit of Murisipántepui is heavily fractured, the northernmost part of the tepui summit being inaccessible by foot from the southernmost part. The total summit area is less than 0.5 km 2. The new species is expected to occur on Tereke-Yurén-tepui and Kamarkawaraitepui (see Fig. 2A ), which have common slopes with Murisipán-tepui.

Riolama inopinata sp. nov. is diurnal and inhabits patches of dense vegetation on the tepui summit. The holotype was collected during a foggy morning while active in a patch of dense vegetation surrounded by bare sandstone rock. The paratype was collected earlier on the same morning while crawling among pitcher plants ( Heliamphora folliculata ) at the edge of the lake present in the middle of Murisipán-tepui ( Fig. 3D ). Prior to the discovery of R. inopinata sp. nov. the only reptile reported from Murisipán-tepui was Arthrosaura testigensis Gorzula & Señaris, 1999 , a species also reported from Tereke-Yurén-tepui.

PHYLOGENETIC POSITION OF THE GENUS RIOLAMA

Maximum-parsimony, maximum-likelihood, and Bayesian analyses of the concatenated and single-gene data sets resulted in similar tree topologies, and are mostly congruent with existing phylogenetic studies of Gymnophthalmidae (e.g. Pellegrino et al., 2001; Castoe et al., 2004; Rodrigues et al., 2005), except for a few poorly supported nodes (see below). None of the molecular analyses performed in this study support Riolama as a member of the subfamily Cercosaurinae as postulated by Pellegrino et al. (2001) and Castoe et al. (2004) based on overall morphological similarities ( Riolama was not included in these molecular phylogenetic analyses). Instead, Riolama is always recovered as ‘basal’ to the clade ( Cercosaurinae (Gymnophthalminae + Rachisaurinae)) ( Fig. 8 ), although that node is poorly supported in MP, BA, and ML. Incongruence in tree topologies with previous molecular phylogenetic studies mostly concern the phylogenetic position of: (1) Bachia , which was either found sister to Ecpleopodini + Cercosaurini in BA and ML (low support) or sister to Cercosaurini in MP (low support), with the latter being congruent with Pellegrino et al. (2001) and Castoe et al. (2004); (2) the clade Gymnophthalminae + Rhachisaurinae was found sister to Cercosaurini in the MP topology (with low support).

As the molecular results do not support Riolama as a member of any described Gymnophthalmidae subfamily, I here propose the erection of a new subfamily to accommodate it, the Riolaminae, as morphologically diagnosed below (see also Fig. 8 ).

Figures

Figure 1. A, map of the Pantepui region, showing the distribution of Riolama species. The white rectangle corresponds to the area enlarged in (B). B, distribution of known Riolama species occurring east to the Rio Caroní (blue lines) in Venezuela and western Guyana. The white rectangle corresponds to the area enlarged in Figure 2A.

Figure 2. A, detailed satellite map of the Los Testigos Massif showing the type locality of Riolama inopinata sp. nov. (blue star) and neighbouring mountains. B, aerial photograph of Murisipán-tepui and neighbouring mountains, taken from the north. Photograph courtesy of C. Brewer-Carías. Satellite maps, ©Google Maps.

Figure 3. Riolama inopinata sp. nov. A, IRSNB 2679, male holotype in life. B, IRSNB 2680, male paratype in life. C, ventral view of the anaesthetized holotype (grid squares = 5 mm). D, lake on the summit of Murisipán-tepui, showing the macrohabitat of the new species (18 June 2012). Photographs by the author.

Figure 4. Hand and foot of Riolama inopinata sp. nov. compared with Riolama leucosticta: (A) left hand and (B) left foot of R. inopinata sp. nov. (holotype, IRSNB 2679) in preservative; (C) left hand and (D) left foot of R. leucosticta (IRSNB 18322) in preservative. Note the different shape of subdigital lamellae. Scale line: 5 mm. Photographs by the author.

Figure 5. Subpelvic region and lateral body of Riolama inopinata sp. nov. compared with Riolama leucosticta. A, subpelvic region of R. inopinata sp. nov. (holotype, IRSNB 2679) in preservative, showing preanal scales and femoral pores (white arrows). B, subpelvic region of R. leucosticta (IRSNB 18322) in preservative, showing preanal scales and femoral pores (white arrows). C, lateral body (trunk) of R. inopinata sp. nov. (holotype, IRSNB 2679) in preservative (head to left). D, lateral body (trunk) of R. leucosticta (IRSNB 18322) in preservative (head to left). Scale lines: 5 mm. Photographs by the author.

Figure 6. Riolama inopinata sp. nov. Drawing of lateral, dorsal, and ventral views of the head of the holotype (IRSNB 2679). Scale line: 5 mm.

Figure 7. Riolama inopinata sp. nov. A, dorsal face of paratype (IRSNB 2680, left) and holotype (IRSNB 2679, right) in preservative. B, ventral face of paratype (IRSNB 2680, left) and holotype (IRSNB 2679, right) in preservative. Scale line: 1 cm. C, comparison between right hemipenes (sulcate faces) of males of Riolama leucosticta (IRSNB 18319, 48.6 mm SVL, left) and R. inopinata sp. nov. (paratype, IRSNB 2680, 42.8 mm SVL right). Scale line: 3 mm. (D) Schematic drawings of asulcate, sulcate, and lateral faces of the right hemipenis of R. inopinata sp. nov. (paratype, IRSNB 2680). HSS, hook-shaped spines; SF, spinulate flounces; SS, sulcus spermaticus. Scale line: 2 mm. Photographs by the author.

Figure 8. Bayesian phylogenetic tree based on the concatenated data set (16S + ND4 + C-mos, totalling 1626 bp). Numbers at the nodes represent statistical support for Bayesian (BA), maximum-likelihood (ML), and maximum-parsimony (MP), respectively. Bootstrap supports below 50% and Bayesian posterior probabilities below 75% are not shown, or are represented by a dash.