Eleutherodactylus (Syrrhophus) coelum sp. nov.

(Fig. 4; Table 3)

El Cielo Chirping Frog / Rana Chirriadora de El Cielo:

Holotype. IBH 36351, an adult male from Gómez Farías (23.042308°N, - 99.154858°W, WGS84), 350 m elevation, in the El Cielo Biosphere Reserve, municipality of Gómez Farías, Tamaulipas, Mexico, collected by C. Omar Becerra Soria and M. Delia Basanta on 13 September 2018.

Paratypes. Five specimens. IBH 36349 and IBH 36352, both adult females, and IBH 36350 and IBH 36353 adult males from the same locality and recollection data as the holotype. IBH 36354 from Alta Cima (23.064144°N, - 99.202869°N), 950 m elevation, in the El Cielo Biosphere Reserve, Gómez Farías, Tamaulipas, Mexico, collected by the same individuals than the holotype .

Referred specimens. IBH 30477 from on road from Alta Cima to San José, at 1.7 km NE (by air) of San José (23.06062°N, - 99.22171°W, WGS84), 1382 m, in the El Cielo Biosphere Reserve, collected by Sean M. Rovito, Gabriela Parra-Olea, Thomas J. Devitt, Susan Cameron, Jorge Sánchez, and Elí Garcia-Padilla on 2 August 2010 . IBH 30480 from Centro Interpretativo Ecológico (23.06593°N, - 99.1687°W), 360 m, in the El Cielo Biosphere Reserve, with the same recollection data as the IBH 30477. IBH 32711, an adult male with the same data of the holotype. IBH 32712, an adult male from the same locality and recollection data as the paratype IBH 36354 .

Diagnosis. A member of the genus Eleutherodactylus, subgenus Syrrhophus, in the Eleutherodactylus (Syrrhophus) longipes clade as defined by Hernández-Austria et al. (2022), morphologically most like E. campi, E. cystignathoides, and E. potosiensis . Eleutherodactylus coelum sp. nov. differs from all other species of the subgenus by the following combination of characters: small-size frog with a mean SVL 17.27 mm ± 1.54 in eight adult males (range 13.51–19.88 mm) and mean SVL 16.64 mm ± 0.68 in two adult females (range 16.16–17.12 mm); interorbital bar present (Fig. 4A); snout truncate in lateral view, and rounded in dorsal view; tympanum membrane round and annulus distinct, interrupted above (Fig. 4B); Finger I shorter than Finger II; fingertips truncated with pads having a terminal groove; Finger III and IV having dilated pads 1.4–2.3 times width of the narrowest part of these fingers (Fig. 3C); palmar subarticular tubercles large and conical; outer metatarsal tubercle round, conical, 1.3–2.2 times larger than the ovoid inner metatarsal tubercle; skin of the dorsum granular; diffuse dark-colored transverse bands in legs.

Comparisons. We limited our comparison to members belonging to the E. longipes species clade. Eleutherodactylus coelum sp. nov. differs from other species of the E. longipes species clade in the following characters (condition of E. coelum sp. nov. in parenthesis).

Eleutherodactylus sp. Ahuacatlán differs from E. coelum sp. nov. by having a larger size, one female with SVL 23.07 mm (females SVL 16.16–17.12 mm), and a smaller tympanum, TD/EW=0.16 (TD/EW 0.91); E. dennisi has a larger size, one male with SVL 24.64 mm and males SVL 31.36–34.83 mm (males SVL 13.51–19.88 mm and females SVL 16.16–17.12 mm), digital tips of the Finger III and Finger IV expanded 3.1–3.7 times width of the narrowest part of these same fingers (digital tips of the Finger III and Finger IV expanded 1.4–2.3 times width of the narrowest part of these same fingers), and by having a dorsal coloration light brown to tan with brown vermiculations (dorsum with brown markings without forming vermiculations).

Eleutherodactylus cystignathoides differs from E. coelum sp. nov. by having a smaller tympanum, TD/ EW= 1.03 in males and TD/EW= 0.74 in females (TD/EW= 1.14 in males and TD/EW= 0.91 in females), smaller tibia, TL/SVL= 0.46 in males and TL/SVL= 0.43 in females (TL/SVL= 0.50 in males and TL/SVL= 0.47 in females), and rounded subarticular tubercles (conical subarticular tubercles); E. campi has a coarsely granular dorsum (less granular dorsum), generally no interorbital bar (interorbital bar present), and rounded subarticular tubercles (conical subarticular tubercles); E. potosiensis has a larger size, with males SVL 21.23–23.16 mm and females SVL 22.82– 27.24 mm (males SVL 13.51–19.88 mm and females SVL 16.16–17.12 mm), digital tips of Finger III and Finger IV expanded 1.52–1.72 times width of the narrowest part of these same fingers (digital tips of Finger III and Finger IV expanded 1.4–2.3 times width of the narrowest part of these same fingers), and belly unpigmented, without markings (belly with a few brown markings).

Eleutherodactylus longipes differs from E. coelum sp. nov. by having a larger size, with males SVL 22.1–33.2 mm and females SVL 26.8–39. 6 mm (males SVL 13.51–19.88 mm and females SVL 16.16–17.12 mm), digital tips of Finger III and Finger IV greatly expanded, more than twice the width of the narrowest part of these same fingers (digital tips of Finger III and Finger IV expanded 1.4–2.3 times width of the narrowest part of these same fingers), and dorsum with irregular brown blotches, spots, or reticulations on a light background (dorsum with scattered olive-brown markings without forming vermiculations on light background); E. leprus has a larger size, with males SVL 20.5–26.5 mm and females SVL 22.0– 29.3 mm (males SVL 13.51–19.88 mm and females SVL 16.16–17.12 mm), dorsum with brown, yellow or green blotches or spots forming reticulations on a dark background (dorsum with scattered olive-brown markings without forming vermiculations on a light background); E. marnockii has a larger size, with males SVL 18.4–28.9 mm and females SVL 20.4–35.4 (males SVL 13.51–19.88 mm and females SVL 16.16–17.12 mm), and dorsum tan to light brown with rusty-brown marks (dorsum with scattered olive-brown markings on light background), and interorbital bar absent (interorbital bar present); E. guttilatus has a larger size, with males SVL 20.6–29.0 mm and females SVL 25.7–31.0 mm (males SVL 13.51–19.88 mm and females SVL 16.16–17.12 mm), lumbo-inguinal gland present (lumbo-inguinal gland absent), areolate ventral skin (smooth ventral skin); E. verrucipes has a larger size, with males SVL 17.5–26.1 mm and females SVL 28.0– 31.7 mm (males SVL 13.51–19.88 mm and females SVL 16.16–17.12 mm), and lumbo-inguinal gland present (lumbo-inguinal gland absent), areolate ventral skin (smooth ventral skin), and interorbital bar absent or present (interorbital bar present). General characteristics for the E. longipes species clade are given in Table 3.

Description of the holotype. Adult of small size (18.7 mm); head longer than wide (HL 7.62 mm vs. HW 7.16 mm); interorbital bar diffuse (Fig. 4A); snout truncate in lateral view (Fig. 4B), and rounded in dorsal view; nostrils small, directed laterally and much nearer the tip of snout than the eye; eyes large, with a length similar to the END (EL 2.3 mm vs END 2.43 mm), prominent, directed laterally; lower lip with a few pale spots; tympanum distinct, circular, its annulus not interrupted above and membrane visible; tympanum large, spans 80% of the eye; poorly developed supratympanic fold; a pair of low, and rounded postrictal tubercles; vocal slits present; subgular vocal sac not evident. Forelimbs relatively short and slim; fingers lack interdigital webbing; Finger I shorter than Finger II; fingertips truncated and expanded; digital pad on Finger III expanded 1.7 times the width of the narrowest part of that same finger; palmar subarticular tubercles large and conical (Fig. 4C); three palmar tubercles: inner palmar tubercle slightly projection in elevation, oval middle palmar tubercle, and outer palmar tubercle almost imperceptible; supernumerary tubercles are not numerous (Fig. 4C). Inguinal gland absent; skin on dorsum granular and venter smooth, and areolate in flanks. Hindlimbs are long; when the leg is extended forward along the body, the heels reach the anterior corner of the eye; the inner metatarsal tubercle is large and elongated; the outer metatarsal tubercle is small, 1.5 times the size of the inner, slightly prominent; tips of the toes truncated; toes lack interdigital webbing (Fig. 4D).

Coloration of the holotype in preservative. Lateral aspect of the canthus rostralis with a stripe Sepia (279) that fades inferiorly to Olive-Brown (278); the stripe extends posterior to the eye across the tympanum; interorbital bar Olive-Brown (278); dorsal background of head, body and limbs Light Buff (2); many Olive-Brown (278) markings on the back with two ill-defined longitudinal bands Light Buff; legs with irregular transverse dark bands Olive-Brown (278); venter surface Pale Buff (1); chin, ventral surface of thighs and legs sprinkled with Vandyke Brown pigment (281).

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Coloration in life (from photos, but not of the holotype). Dorsal surface of the head Drab (19) which fades from interorbital bar to Glaucus (272); a Vandyke Brown (282) irregular interorbital bar; dorsal surfaces of head and body with Vandyke Brown (282) markings; back Smoke Gray (267) with two ill-defined longitudinal bands Salmon Color (58); dorsal surface of arms with Salmon Color (58) spots; legs with transverse bands of Vandyke Brown (282) on a Salmon Color (58) to Smoke Gray (267) background; iris Light Yellow Ocher (13).

Measurements of the holotype (measurements in mm). SVL 18.7, HL 7.62, HW 7.16, EW 1.38, END 2.43, IOD 2.59, TD 1.86, EL 2.3, IND 2.02, FoL 5.23, HaL 4.21, IPTL 0.72, MPTL 0.8, OPTL 0.18, F3L 3.85, F3PW 0.64, F4PW 0.67, FeL 8.51, TL 9.29, IMTL 0.84, OMTL 0.56, FL 8.61, T4L 7.62, T4PW 0.76.

Variation. Variations in the morphometric data of the type series and species compared are summarized in Table 4. We observed little variation in coloration and no evident morphological differences among the nine paratypes. The dorsal background of IBH 32711–32712 and IBH 36349–36350 is paler than the holotype. The interorbital bar in IBH 30477 and IBH 36352–36353 is fainter than the holotype; in the IBH 32711–32712 is narrow and well-defined. The two dorsal longitudinal bands in IBH 36353–36354, IBH 30477, and IBH 30480 are not visible. There are no transverse dark bands on the legs of IBH 36533 and IBH 32711 .

Distribution and natural history. Eleutherodactylus coelum sp. nov. is known for the locality Alta Cima and from Gómez Farías, in the El Cielo Biosphere Reserve, in southwestern of the state of Tamaulipas, Mexico (Fig. 1), in the foothills of the Sierra Madre Oriental known as Sierra de Cucharas and Sierra Chiquita. The species occurs from low to moderate elevations (approximately 350–1382 m elevation) in the subtropical evergreen and mountain cloud forests. Specimens have been found on top of bush leaves (Fig. 5), under rocks along a dry river, and on top of water containers that local people name canoas. It must be a nocturnal species like its congeners. The individuals collected in September 2018 were seen during the day under rocks and were not emitting any advertisement calls; however, this species is likely to be acoustically active like other species in the E. longipes species clade and other congeners. In two specimens (IBH36349–36350), we found remnants of insects (coleopterans and formicids), malacostracan (isopods), and arachnids (spiders and pseudoscorpions). It occurs in sympatry with Chiropterotriton cieloensis, C. cracens, Aquiloeurycea scandens, and Isthmura bellii (Rovito & Parra-Olea 2015) .

Conservation status. We recommend that E. coelum sp. nov. it be designated as Critically Endangered (CR) based on criterion B1ab(iv) (extent of occurrence <100 km 2, and number of localities) of the International Union for the Conservation of Nature Red List (IUCN, 2022).

Etymology. The specific epithet coelum (in Latin) means heaven in allusion to the Reserva de la Biosfera El Cielo, where the species occurs (El Cielo means heaven in Spanish).