Odontophrynus reigi, Rosset et al.

Mancino, Mercedes, Baldo, Diego, Alcalde, Leandro, Borteiro, Claudio, Kolenc, Francisco, Oliveira, Luciana G. & Rosset, Sergio D., 2025, Description of the external morphology and buccopharyngeal cavity of the tadpole of Odontophrynus reigi (Anura: Odontophrynidae), Zootaxa 5696 (1), pp. 142-150 : 142-150

Tadpoles of Odontophrynus reigi were collected in several temporary ponds in Misiones, Argentina.

Localities and acronym numbers of the studied specimens are detailed below (Appendix 1). They are housed at the Laboratorio de Genética Evolutiva (LGE) “Claudio Juan Bidau”of the Instituto de Biología Subtropical (CONICET-UNaM), Facultad de Ciencias Exactas Químicas y Naturales, Universidad Nacional de Misiones (UNaM). After capture, they were anesthetized with 2% lidocaine and fixed in 10% formalin, following recommendations by the Ethics and Integrity Committee of UNaM (16Q1314-PI). Species identity was based on specimens reared to metamorphosis and adults found in breeding activity in these localities. Larvae were staged according to Gosner (1960; GS hereinafter). The description of the external morphology and the measurements were based on 30 tadpoles from Posadas, Capital Department (LGE 22375). We took six measurements following McDiarmid & Altig (1999): total length (TL), body length (BL), tail length (TAL), maximum tail height (MTH), tail muscle height (TMH), and tail muscle width (TMW). Besides, we took 15 measurements following Lavilla & Scrocchi (1986): body maximum width (BMW), body width at nostrils (BWN), body width at eye level (BWE), body maximum height (BMH), rostrospiracular distance (RSD, measured with modifications, horizontally from the tip of the snout to the posterior edge of the spiracular tube), frontonasal distance (FN), eye-nostril distance (END, measured with modifications, from the posterior edge of nostrils to the anterior edge of eyes), nostril major axis (N), eye diameter (E), intranasal distance (IN), intraocular distance (IO), extranasal distance (EN), extraocular distance (EO), oral disc width (OD), and dorsal gap length (DG). These morphometric variables were measured to the nearest 0.1 millimeters using an ocular micrometer under a stereoscopic microscope, except for TL, BL, and TAL, which were measured with a digital caliper. Oral disc and labial tooth row formula (LTRF) were examined in the 30 tadpoles from Posadas and additionally, in eight tadpoles from Manantial, Capital Department (LGE 25565, 25567). Coloration in life was described based on one tadpole from Santa Cecilia, Candelaria Department (LGE 17056). Additionally, the oral disc and the buccopharyngeal cavity were examined in detail in one tadpole from Manantial (LGE 25567) that was prepared for Scanning Electron Microscopy (SEM) following the protocol of Alcalde & Blotto (2006). As complementary information, we studied the buccopharyngeal cavity of two other tadpoles from Manantial and three tadpoles from Posadas, dissecting them following Wassersug (1976) and using 1% methylene blue solution for contrast. Terminology and delimitation of character states (e.g., small, medium, large) follow McDiarmid & Altig (1999) and Pezzuti et al. (2021) for external morphology and Wassersug (1976) and McDiarmid & Altig (1999) for buccopharyngeal cavity. Morphological comparisons with the tadpoles of the other species of the O. asper group were made with the data available in the literature (for O. juquinha Rocha et al. and O. toledoi Moroti et al. ) and also with new samples (for O. asper , O. cordobae Martino & Sinsch , O. lavillai Cei , and O. maisuma Rosset ; Appendix 1).

External morphology ( Fig. 1 ). Tadpoles of Odontophrynus reigi at GS 31–39 (LGE 22375) have 41.1 ± 6.41 mm of TL. Body depressed (BMH/BMW = 0.71–0.91), from elliptical to ovoid in dorsal view, globular depressed in lateral view, widest between the middle and the posterior third of the body, and shorter than half of the total length (BL/TL = 0.36–0.42). Snout oval in dorsal view (BWN/BWE = 0.67–0.77), rounded in lateral view. Small to medium-sized eyes (E/BWE = 0.12–0.23), located dorsally (EO/BWE = 0.54–0.73), and directed dorsolaterally or anterolaterally. Medium-sized nostrils (N/BL = 0.03–0.05; N/BWN = 0.07–0.12), from rounded to slightly elliptical, with a small fleshy projection on the medial margin. Nostrils located dorsally (EN/BWN = 0.28–0.46), directed anterodorsally or anterolaterally, scarcely visible laterally, and positioned at mid-distance between the eyes and the tip of the snout (FN/END = 0.67–1.6). Spiracle sinistral, short, located lateroventrally, with its inner wall being entirely fused to the body. Spiracle opening oval, posterodorsally directed, and placed in the middle third, slightly posterior to the half of the body (RSD/BL = 0.55–0.70). Intestinal tube circularly coiled, with a switchback point located at the center of the abdominal region. Vent tube subcylindrical originated medially, reaching the free margin of the lower fin and opening dextrally. Tail slightly longer than half of the total length (TAL/TL = 0.57–0.64), nearly as high as the body (MTH/BMH = 0.96–1.32). Dorsal fin originated at tail-body junction, with convex margin and maximum height at mid-length; ventral fin lower than dorsal, originated at the vent tube level, with gently convex margin; tail tip acute (n = 18), nearly rounded (n = 9), or rounded (n = 3). Tail musculature slender (TMH/BH = 0.27–0.49). Oral disc anteroventral, medium-sized (OD/BMW = 0.28–0.44), laterally and lateroventrally emarginate ( Fig. 1D , 3A ). Marginal papillae of similar size, nearly conical, with a pointed or blunt tip, arranged in a single row with a wide dorsal gap (DG/OD = 0.64–0.90). Submarginal papillae variable, on the supraangular region (in 3 specimens), infraangular region (1–3; n = 12), or both (4–7; n = 7). Most frequent LTRF 2(2)/3(1) (n = 27), but some specimens with 2/3(1,3) (n = 1, GS 37), 2(2)/3(1,2) (n = 1, GS 38), and 2(1,2)/3(1) (n = 1, GS 39). Jaw sheaths narrow, finely serrated on margins, upper jaw sheath arc-shaped, entirely colored; lower jaw sheath V-shaped, colored on its upper half. In most tadpoles, the anterior tooth rows, A-1 and A-2, were of the same length, and the posterior tooth rows, P-1 (not visible in SEM photograph) and P-2, were also of the same length, longer than P-3, which was 50–70% the length of the others. Tadpoles from Manantial were more variable in LTRF: 2(2)/3(1) (n = 2, GS 31 and 39), 2/3(1) (n = 3, GS 32), 2(2)/3(1,3) (n = 2, GS 32 and 36), and 2(2)/3(1,2,3) (n = 1, GS 35).

Measurements (in mm). Values for 30 tadpoles (GS 31–39; LGE 22375) are presented as mean ± SD, with range in parentheses: TL = 41.1 ± 6.41 (27–59); BL = 16.38 ± 2.7 (11–23.8); TAL = 24.92 ± 3.87 (16.4–34.7); MTH = 9.3 ± 1.83 (5.5–14.6); TMH = 3.98 ± 0.82 (2.4–5.9); TMW = 3.13 ± 0.54 (1.9–4.4); BMW = 9.97 ± 1.98 (6.9–16.5); BWN = 6.53 ± 1.14 (4.7–10.1); BWE = 9.11 ± 1.46 (6.7–13.4); BMH = 8.15 ± 2.01 (5.1–14.6); RSD = 10.08 ± 1.51 (7.1–13.9); FN = 1.77 ± 0.45 (0.93–2.73); END = 1.7 ± 0.31 (1–2.47); N = 0.62 ± 0.12 (0.4–1); E = 1.71 ± 0.27 (1.13–2.6); IN = 1.81 ± 0.3 (1.2–2.47); IO = 4.26 ± 0.8 (2.6–7); EN = 2.48 ± 0.27 (1.8–3); EO = 5.57 ± 0.88 (4–8.4); OD = 3.75 ± 0.45 (2.73–4.67); DG = 2.72 ± 0.27 (2.05–3.25).

Coloration. In life ( Fig. 2 ), body light brown, dorsally and laterally, densely pigmented with small, rounded, and dark brown and greenish blotches, and iridophores that give a copper orange brightness. Black iris scattered with small copper spots and two larger whitish blotches below the pupil; narrow and bronze pupil ring. Tail with scattered big, rounded, and dark brown blotches with a diffuse lighter brown all around. Tail muscle cream, lighter than the body, fins opalescent. Fins with a reticulation of small whitish marks. A big dark brown blotch at the center of the first four myomeres, and a series of equidistant dark brown blotches along the margins of musculature. Ventral fin with longitudinal unspotted opalescent stripe just below the musculature, reaching 1/2 of the tail length. In preservative ( Fig. 1 ), light brown dorsal body, lighter in the anterior region, with a dark brown perinarial region. Black iris with white pupils. Dark brown spots were evenly distributed on the tail muscle and fins. Caudal musculature light brown, fins translucent. Vena caudalis lateralis evident. Abdominal region transparent.

Buccopharyngeal cavity. Buccal floor nearly triangular, as wide as long ( Fig. 3B ). Two pairs of infralabial papillae of similar size, relatively high, transversely aligned except in one specimen (GS 39; LGE 22375) where the medial pair was positioned more anteriorly. The medial pair slightly conical, simple, and with serrated edges (not visible in the SEM specimen). The lateral pair, thicker, bifurcated with serrated edges ( Fig. 3C ) or multiple branching with two major central projections and serrated edges in one specimen (GS 36; LGE 25567). Tongue anlage oval with four lingual papillae in a transverse row, usually the medial ones larger than the lateral, and with serrated edges. One specimen (GS 34; LGE 22375) with papillae aligned to form a semicircle; another specimen (GS 39; LGE 22375) with five papillae, one smaller than the other four. Buccal floor arena delimited by papillae arranged in a semicircular shape, with approximately 60 pointed, medial or anteriorly oriented papillae, 10 large, 20 medium-sized, and nearly 30 small, and more than 100 pustulations scattered among them. Buccal pockets elongate, obliquely oriented, with nearly five pre-pocket papillae and 10 pustulations. Ventral velum well developed, with distinct, relatively large, digitiform marginal projections. Six of these projections were closer to each other in the middle. Medial notch not evident.

Buccal roof nearly diamond-shaped, longer than wide ( Fig. 3C ). Prenarial arena with two inconspicuous semicircularshaped transversal ridges. Choanae transversely oriented, with small prenarial papillae and posterior wall with a smoothedged narial valve. Postnarial arena smaller than prenarial arena, with 3–4 pairs of relatively large papillae and 3–5 small papillae among them. Median ridge as a wide semicircular flap with a smooth or serrated edge usually concealing 1–3 small postnarial papillae. Large lateral ridge papillae bi- or trifurcate, with 1–3 small secondary projections on the anterior margin. Buccal roof arena nearly circular, with papillae arranged in a U-shaped pattern and oriented toward the center, including nearly 10 large and 10 small papillae, and more than 100 pustulations uniformly distributed across the central area and among the papillae. Groups of 5–6 lateral roof papillae posterolateral to the arena. Dorsal velum divided by a deep medial notch, bearing five medium-sized projections on its terminal portion.

Odontophrynus reigi :

ARGENTINA: MISIONES PROVINCE: CANDELARIA DEPARTMENT: Santa Cecilia ( 27°29'35.41"S, 55°40'43.48"W, 125 m a.s.l): LGE 17056. CAPITAL DEPARTMENT: Manantial , Ruta Provincial 105 , Km 28 ( 27°41'21"S, 55°48'12"W, 146 m a.s.l.): LGE 25565, 25567. Posadas , Avenida 213 and Calle 242 ( 27°26'46.82"S, 55°57'31.47"W, 159 m a.s.l.): LGE 22375 .

Figures

FIGURE 1. (A) Lateral, (B) dorsal, and (C) ventral views of a tadpole of Odontophrynus reigi in preservative (GS 38, LGE 22375). (D) Oral disc of a tadpole at GS 35 from the same locality.

FIGURE 2. Lateral view of a tadpole of Odontophrynus reigi in life (GS 38, LGE 17056).

FIGURE 3. Scanning Electron Microscopy photographs of (A) oral disc, (B) buccal floor, and (C) buccal roof of the tadpole of Odontophrynus reigi (GS 32, LGE 25567). Abbreviations:A-1, A-2 = first and second anterior (upper) tooth rows, bfa = buccal floor arena, bfp = buccal floor arena papillae, bp = buccal pocket, bra = buccal roof arena, brp = buccal roof arena papillae, c = choana, dv = dorsal velum, ip = infralabial papillae, le = lateral emargination, lj = lower jaw sheath, lp = lingual papillae, lrip = lateral ridge papillae, lrop = lateral roof papillae, lve = lateroventral emargination, mp = marginal papillae, mr = median ridge, P-2, P-3 = second and third posterior (lower) tooth rows, p = pustulation, poa = postnarial arena, pop = postnarial arena papillae, pp = prepocket papillae, pra = prenarial arena, prp = prenarial arena papillae, uj = upper jaw sheath, vv = ventral velum, vvp = ventral velum papillae.