Among pipids, P. parva is moderately small, with female snout-vent length (SVL) ranging from 27 to 44 mm and male SVL ranging from 28 to 37 mm. The head is narrow, with large eyes, and the snout is pointed. As is the case for all other pipids, the tongue is lacking, and the upper lip has a labial pocket at the angle of the jaw. Teeth are absent on both the pre-maxilla and maxilla (Trueb and Cannatella 1986). The body is slender and less depressed relative to other Pipa (Trueb and Cannatella 1986). The skin is covered with small protuberances, or tubercles, of varying size, density, and definition. On the head, tubercles tend to be smaller but uniform in size and distribution, while on the back they are dense and large. Upper surfaces of the limbs also have large tubercles, though not as numerous. Ventral tubercles are generally less prominent and less dense (MCZ specimens; Trueb and Cannatella 1986). On the feet, recurved spinose tubercles are present on the inner first toe and outer fifth toe, as well as on the tarsus, and smaller recurved spinose tubercles are present on the plantar surface (Trueb and Cannatella 1986).
The fingertips of Pipa generally and P. parva specifically are quite distinctive. Pipids have evolved uniquely modified lobes on the end of each fingertip, with the exact form and location of these lobes varying by species. Pipa parva displays four distinct lobes asymmetrically distributed on the fingertip. One pair of lobes is terminally located while the other is slightly proximal and on the palmar surface (MCZ specimens), distinguishing this species from all other pipids (Trueb and Cannatella 1986). In addition to unique fingertips, P. parva (and all other pipids except P. pipa and P. snethlageae) have keratinous tips on toes I-III, a relatively rare feature among amphibians (Duellman and Trueb 1994). On the feet of five of the seven species of Pipa, there is an inner metatarsal tubercle, which ranges from well developed (as in P. pipa) to less developed (as in P. aspera). However, the inner metatarsal tubercles are absent altogether in P. parva and P. myersi (Trueb and Cannatella 1986).
Pipa parva has several series of lateral line organs. One series extends from the snout to the anterior margin of each eye, with an additional organ or two associated with the dorsal or ventral margins of the eye. Another series, with vertically oriented organs, commences at each side of the head at the angle of the jaw, and runs posteriorly from the jaw over the forearm and along the ventral side of the flank. A paired, longitudinal series runs from the temporal region of the head down the dorsum. Yet another longitudinal series extends from each forearm along the dorsal side of the flank (Trueb and Cannatella 1986).
The skull is longer than it is wide, and relatively elongate compared to other pipid species, though still possessing the characteristic wedge shape. Unlike most species of Pipa, P. parva does not possess a palatine process of the maxilla or pre-maxilla. In addition, the pre-articular mandibular bones are relatively straight (compared to those of P. snethlageae and P. pipa, which have a medial curve), giving P. parva its ventrally narrow snout. The presacral vertebral column of Pipa parva also shows some differences from other pipids. In all Pipa, vertebrae are imbricate and opisthocoelous. The sacrum and urostyle are fused, and the sacral diapophyses are hugely elongated in the anterior-posterior direction. However, the ventral anterior margin of the presacral I (Atlas) has convex articulation in P. parva (as in P. myersi, and P. snethlageae), while other pipids have straight or somewhat concave articulation (Trueb and Cannatella 1986). The pelvic girdle of Pipa is distinctive as a genus, with only slight modification among species: P. parva has dorsolaterally oriented ilial crests (as is the case for P. pipa and P. snethlageae), rather than the completely depressed or lateral iliac crests found in other species of Pipa. As in all Pipa, Pipa parva has a modified arciferal pectoral girdle (Trueb and Cannatella 1986).
In preserved specimens, these frogs have a dorsally uniform dark brown coloration on the head, back, limbs and associated tubercles. Ventrally, the dark brown fades into a light gray/tan, and may be unspotted or have sparse indistinct spots on the pectoral region (MCZ specimens, Trueb and Cannatella 1986). Some specimens have been reported as brown with tan tubercles and scattered dark brown spots (Trueb and Cannatella 1986), or blackish gray dorsally with obscure darker spots, and grayish white ventrally, with some spotting on the flanks and throat (Ruthven and Gaige 1923). While the feet have the same coloration, the webbing between the fingers and toes is completely transparent (MCZ specimens; Trueb and Cannatella 1986).
Tadpoles of P. parva reach about 40 mm in length. The mouth structure is about half the head width and is terminal, slightly toward the ventral side of the head. Notably, P. parva lacks the opercular flap extending across branchial slit II. Thus, internal gills are absent and forelimb development is external and visible. The skull and jaws are largely composed of embryonic cartilage and are long, broad and flat. Tadpoles are dark gray-brown dorsally, with transparent ventral surfaces (Sokol 1977).
Karyotype, 2n=30 (Cannatella and de SÃ¡ 1993).
The species Pipa parva was originally described by Ruthven and Gaige (1923).
The specimens used for observation are located at the Harvard Museum of Comparative Zoology. The catalog numbers and locality are as follows: Venezuela A-9012, A-44812, A-44813, A-44814, A-136509.