Elachistocleis araios, Sánchez-Nivicela & Peloso & Urgiles & Yánez-Muñoz & Sagredo & Páez & Ron, 2020

Sánchez-Nivicela, Juan C., Peloso, Pedro L. V., Urgiles, Verónica L., Yánez-Muñoz, Mario H., Sagredo, Yerka, Páez, Nadia & Ron, Santiago, 2020, Description and phylogenetic relationships of a new trans-Andean species of Elachistocleis Parker 1927 (Amphibia, Anura, Microhylidae), Zootaxa 4779 (3), pp. 323-340 : 329-333

Elachistocleis araios sp. n.

Holotype. ( Figs. 3–5 , 7 ) QCAZ 56485 , an adult female, from La Independencia, 3.0583° S, 79.7171° W ( WGS84 ), 308 m a.s.l., Ponce Enriquez canton, Azuay province, Ecuador ( Fig. 3 ). Collected by Juan C. Sánchez-Nivicela and Daniel Navas on December 14, 2009.

Paratype. ( Figs. 3 , 6–7 ) QCAZ 74764 , an adult female from Cooperativa 23 de Noviembre, Cerro de Hayas 2.7174° S, 79.6285 W ° ( WGS84 ), 57 m a.s.l., Naranjal canton, Guayas province, Ecuador ( Fig. 3 ). Collected by Yerka Sagredo on February 6, 2019 .

Diagnosis. A small species of Elachistocleis (SVL in females = 25.7–26.1 mm, n = 2; males unknown), characterized by an ovoid body form ( Fig. 4 , 6 ), triangular head, slightly wider than long, and a barely developed occipital fold ( Fig. 5 A–B). Snout rounded in dorsal and lateral views; canthus rostralis slightly concave and loreal region is convex; nostrils laterally oriented ( Fig. 5 A–B). Postcommissural glands inconspicuous. Tympanic annulus, tympanic membrane, and dentigerous process of vomer absent. Upper jaw more projected than the lower jaw, tongue is big, ovoid, and covers the entire buccal cavity. Choanae rounded and widely separated, oriented to the anterior region of buccal cavity. Arms slender without tubercles on forearm. Hands ( Fig. 5C ) lack interdigital membranes and supernumerary tubercles; first finger almost the same size as the second, both almost as long as finger IV, finger lengths are I<II<IV<III; subarticular tubercles, ovoid and as wide as fingers, prominent thenar tubercle, palmar tubercle longitudinally divided. Foot ( Fig. 5D ) lacks interdigital membranes and supernumerary tubercles, toes lack discs. Inner plantar tubercle same size as subarticular tubercles; relative toe lengths I<II<V<III<IV. TBL is slightly longer than THL. Dorsal surface of body and fingers lack dermal spines. Cloacal region lacks glands and tubercles.

Comparisons. The new species can be immediately distinguished from most Elachistocleis species in having an immaculate venter (variably pigmented or blotched in E. bumbameuboi , E. carvalhoi , E. corumbaensis , E. erythrogaster , E. magnus , E. ovalis , E. pearsei , E. piauiensis , E. skotogaster , E. surinamensis , and E. surumu ). Elachistocleis araios is, therefore, most similar to E. bicolor , E. cesarii , E. haroi , E. helianneae , E. matogrosso , E. muriaquitan , and E. panamensis in a having uniform, immaculate, ventral coloration. Elachistocleis araios is distinguished from Elachistocleis bicolor , E. cesarii , E. corumbaensis , E. helianneae , E. matogrosso , and E. muriaquitan by its dorsal color patters, E. araios mottled grey with a paravertebral symmetric pattern (dark dorsal coloration, which can vary from uniformly grayish to dark grey with scattered lighter spots).

The new species is further distinguished from E. bicolor , E. corumbaensis , E. matogrosso , and E. muriaquitan in not having any light spot in the axillae and groin (light spot present). It also differs from E. bicolor , E. corumbaensis , and E. haroi in having grayish cream venter and hidden surfaces of limbs (bright yellow coloration on venter and hidden surfaces of limbs on the other species). Moreover, E. bicolor also lacks a mid-dorsal stripe, which is notorious in the new species (but note that this character might be variable in several microhylid species, and that our sample size for E. araios is fairly small).

Elachistocleis araios differs from most species of the genus in having slender fingers and toes with slightly expanded, rounded tips (robust fingers and toes, with tips more narrow than the width of the fingers in E. corum- baensis, E. surinamensis , E. ovalis , E. skotogaster , E. piauiensis , E. panamensis , E. muriaquitan , E. magnus , E. erythrogaster ). In the new species, FI almost the same size as FII, both almost as long as finger IV (FI much smaller than the second, both shorter than FIV in E. haroi ). E. araios differ from several species in having the postcommissural gland poorly developed (massive or large postcommissural glands in E piauiensis , E. magnus , E. erythrogaster , helianneae , E. surumu , E. carvalhoi , E. bumbameuboi , E. cesarii / absent in E. skotogaster ). The new species lack a dorso-lateral fold (present in E. cesarii , E. helianneae , E. surumu , E. carvalhoi , E. bumbameuboi , E. matogrosso , E. bicolor , E. skotogaster , E. magnus , E. muriaquitan , E. corumbaensis , E. pearsei ). Interdigital web absent in E. araios (present, rudiment in E. pearsei ).

Elachistocleis araios ( Figs. 7 A-B) is most similar externally to E. panamensis ( Fig. 7C ), from which is differs by the following combination of characters: a short and rounded snout in E. araios (long and truncate snout in E. panamensis ); present, although weak, lateral fringes in TIV (absent); thenar tubercle small and rounded (large and oval); inner metatarsal tubercles small and rounded (big and oval); dorsal color patterns with dark spots without defined patterns (generally a repetitive triangular design or a large irregular spot in the middle of the back); venter immaculate (cream with clear spots poor visible); grayish-brown, ash-looking, throat and chin—differs from ventral pattern (brown-cream with white spots—same as venter).

Description of the holotype. Adult female ( Fig. 4–5 , 7A ). Body ovoid, skin smooth. Head small, HL 20.2% of SVL, 85.2% of HW. Snout prominent, projected beyond the mouth, protruding in lateral view. Tiny eyes, slightly prominent. Nostrils small, laterally oriented. Canthus rostralis slightly concave and convex in loreal. Complete occipital fold. Postcomissural glands poorly developed. Upper jaw projected beyond lower jaw.

Arms robust, short, without tubercles, a thick ulnar fold present. Fingers slender, short. Relative lengths of fingers: I<II<IV<III. Subarticular tubercles round. Palmar tubercle longitudinally divided, internal section rounded and external ovoid, four times larger than thenar tubercle. Supernumerary tubercles absent. Lateral fringe on fingers weak. Finger tips rounded, weakly expanded. Posterior extremities without tubercles, tarsal fold present. Legs short, robust. Thigh larger than shank, but shorter than foot length. Toes slender. Relative toes lengths: I<II<V<III<IV. Subarticular tubercles round. Supernumerary plantar tubercles absent. Lateral fringe on toes weak. Inner metatarsal tubercle oval. Outer metatarsal tubercle absent. Toes tips rounded, weakly expanded. Tips of fingers and toes with terminal rounded discs. Interdigital web of hands and foots absent. ( Fig. 5 C–D).

Measurements of the holotype in mm: SVL 25.7; HL 5.0; HW 6.1; ED 1.8; IOD 2.7; IND 1.4; END 2.1; THL 9.9; TBL 11.0; FL 12.4; HDL3 5.2; HDL4 3.6; FAL 4.3; FD3 0.5; FT4 0.7.

Variation. Measurement from the paratype in mm: SVL 26.1 ; HL 7.1; HW 6.6; ED 2.8; IOD 2.6; IND 1.6; END 2.3; THL 9.7; TBL 10.7; FL 11.2; HDL3 7.1; HDL4 3.4; FAL 4.4; FD3 0.4; FT4 0.6. The patterns of coloration and design do not represent major differences except that, in the paratype the dorsal line is thinner and less visible in the anterior direction and absent in the head ( Fig. 6 , 7A, 7B ) .

Coloration of the holotype in life. The coloration of dorsum, thighs, shanks, and arms is light brown with small black patches and tiny yellowish-cream dots. A narrow light cream dorsal line extends from the tip of snout to the vent. A thin dorsolateral line resulting from the combination of brown spots extends from the nostrils to the inguinal region and, creates a clearly marked edge between dorsum and flank colorations. Two inguinal spots are present visible from the dorsum. The posterior surface of thighs has a light cream line extending to the inguinal region. Irregular dark brown lines are distributed in thighs, tibia, and feet and, a slightly cream line running along the back of the thighs and across the urostyle bump. Flanks and ventral surfaces of head are light brown with small yellowish-cream spots. Venter is uniform light yellow anteriorly and grayish-yellow posteriorly. Ventral surface of thighs and arms is yellowish cream with light brown ( Fig. 4 ).

Coloration of the holotype in preservative. The coloration of dorsum and forelimbs is uniformly dark brown with few cream spots. The dorsolateral line is not distinguishable; flanks and ventral surface of the head are grayish-cream. The middorsal line is cream, the two black patches on the posterior surfaces of dorsum, the cream line on the thighs, and the irregular dark brown lines in the forelimbs are distinct. The venter is yellowish-cream anteriorly and grayish-cream posteriorly ( Fig. 7 ).

Etymology. The name of the new species is a noun in apposition from the Greek araiós (αραιός) which means scarce, alluding to the fact that it is a difficult species to find in field.

Distribution, natural history and conservation status. Elachistocleis araios is only known from two localities in the lowlands of Azuay and Guayas provinces of Ecuador. The holotype was found in a western foothill forest fragment. The habitat is characterized by the presence of dense vegetation cover with a thick layer of leaf litter and several small streams ( Fig. 8 ). The holotype was collected at night while walking through the leaf litter in a trail of cacao crops near the forest. Sympatric amphibian species included: Epipedobates anthonyi, Lithobates bwana, Leptodactylus labrosus, and Pristimantis achatinus . The paratype and holotype were adult gravid females.

At the type locality, land has been concessioned for mining. Traditional mining is the most common type of mineral extraction in the region. In this process, toxic compounds (e.g., cyanide) and heavy metals (e.g., mercury) are used for extraction and refinement of minerals. Consequently, water bodies, and soils are directly and irreversibly affected. The second locality is a Provincial Natural Recreation Area of 631 ha, but it is an area with strong deforestation pressures.Activities such as cattle ranching and agriculture are widespread in the area as well. Therefore, important extensions of natural vegetation have been replaced with crops and grass. Despite this, we do not have enough evidence to define the degree of threat of this species and we highlight the need for population-level studies to know its status, which is why we recommend that E. araios be listed as Deficient Data on the IUCN Red List.

Figures

FIGURE 3. Map showing records of Elachistocleis araios sp. n. Red square = holotype, Azuay province; red circle = paratype, Guayas province. Ecuador is shown on green on the small map. Black lines represent province boundaries.

FIGURE 4. Holotype of Elachistocleis araios sp. n., female, in life. Above left, Lateral view; below left, dorsal view; right, frontal view.

FIGURE 5. Holotype of Elachistocleis araios sp. n., female, in preservative. (A) Lateral view of head, (B) dorsal view of head, (C) ventral view of right hand, (D) ventral view of right foot.

FIGURE 6. Paratype of Elachistocleis araios sp. n. in life. (A) Profile view, (B) ventral view, (C) dorsal view.

FIGURE 7. Comparison of dorsal (above) and ventral (below) views of Elachistocleis araios sp. n. in preservative. (A) holotype (SLV 25.7 mm); (B) paratype (SVL 26.1 mm); and, E. panamensis, (C) (ICN-48708) female (SVL 23.6 mm).

FIGURE 8. Habitat of the holotype of Elachistocleis araios sp. n.