Pseudis paradoxa

External morphology. Description based on one tadpole at Stage 39 (INPA-H 1650). Total length 204.1 mm. Body ovoid in dorsal view and triangular in lateral view (Fig. 37A, B). Snout truncate in dorsal view and sloped in lateral view. Eyes small, positioned and directed laterally. Nostrils small, oval, dorsally positioned near to snout, with opening anterolaterally directed, without a projection on the marginal rim. Oral disc (Fig. 37C) anteroventral, non-emarginate; marginal papillae triangular, biseriate, with a dorsal gap. Submarginal papillae present laterally. LTRF 2(2)/3(1); A1 and A2 of the same length; P1 and P2 of the same length; P3 shorter. Jaw sheaths moderately wide, finely serrated; anterior jaw sheath arch-shaped, posterior jaw sheath U-shaped. Spiracle single, sinistral, conical, very short, posterodorsally directed, opening in the medial third of the body, with the centripetal wall fused to the body wall and longer than the external wall. Vent tube medial, fused to the ventral fin. Caudal musculature heavy; in lateral view gradually tapering to a pointed tip. Dorsal fin of moderate height, convex, originating on the anterior third of the body, presenting a thick tissue from its beginning until after the eyes level; ventral fin shallow and convex. Tail tip pointed.

Colour. In preservative body gray with brownish-gray spots arranged in a marbled pattern, skin of venter translucent; caudal musculature with brownish-gray spots arranged in a marbled pattern, occasionally appearing the unpigmented, beige colour of musculature, especially on proximal part of tail; fins opaque brownish-gray.

Natural history. The species is found in várzea floodplains.

Comments. Tadpoles of P. paradoxa were described by Kenny (1969) from Trinidad, Duellman (2005) from Peru, Lynch (2006) and Lynch & Suárez-Mayorga (2011) from Colombia, and Schulze et al. (2015) from the lowlands of Bolivia. There are no morphological differences with the descriptions of Kenny (1969) and Lynch (2006). Tadpoles from Santa Cruz, Bolivia (Duellman 2005), differ from those herein characterized by presenting row of marginal uniseriate anterolaterally and biseriate laterally, along a truly short stretch (Fig. 13.13D; Duellman 2005), and a rounded snout in lateral view (Duellman 2005). Tadpoles from Bolivia (Schulze et al. 2015) and from Colombia illustrated by Lynch & Suárez-Mayorga (2011) differ from those herein characterized by, respectively, presenting marginal papilla row biseriate to irregularly aligned triseriate and posterior jaw sheath V-shaped, and a uniseriate row of marginal papillae.

Genus Scarthyla. Only one species of Scarthyla is found in the Central Amazonia.