Hyloxalus idiomelus (Rivero 1991)

In this moderate-sized species of Hyloxalus males attain a snout-vent length of 24.8 mm and females, 27.8 mm. The discs on the fingers are not expanded, and those on the toes are slightly expanded. Fingers I and II equal in length, and Finger III is not swollen in males. Narrow lateral fringes are present on the fingers and toes; a curved inner tarsal fold is present on the distal half of the tarsus. Webbing is absent between the toes. The dorsum is dull tan to rich orange-brown or grayish tan with a green tint and irregular olive brown to black dorsal markings. The dorsolateral stripes are pinkish tan, yellowish orange, or cream; they usually are bordered by dark brown. Oblique and ventrolateral stripes are absent. The flanks are tan to gray; the labial stripe is pinkish cream. The anterior and posterior surfaces of the thighs are yellow to dull orange; the digital scutes are gray, and the iris is dull bronze. The throat, chest, and anterior part of the abdomen are white with dark brown or gray mottling and a yellow suffusion on anterior part of throat; the posterior part of the belly and ventral surfaces of the limbs are yellow. A median lingual process is absent, and the testes are white (Rivero 1991). A tadpole in Stage 34 has a body length of 14.2 mm and a total length of 34.7 mm. Free-swimming tadpoles in Stage 25 may be as small as 8.4 mm in body length and 16.9 mm in total length, whereas tadpoles in Stage 43 may have a body length of 16.3 mm and a total length of 36.6 mm. The body is wider than high; the snout is bluntly rounded in dorsal view and slopes anteroventrally from the level of the orbits to a rounded tip in profile. The small eyes are situated dorsally, directed dorsolaterally, and not visible from below. The spiracle is sinistral with a short tube attached to the body for its entire length; the spiracular opening is directed posterodorsally just below the midline at about midlength of body. The cloacal tube is short, dextral, and attached to the ventral fin. The caudal musculature is moderately robust, approximately uniform in depth on the anterior one-third of the tail, and gradually diminishes distally to a pointed tip. The dorsal fin originates on the base of the caudal musculature, gradually increases in height on the proximal two-thirds of the tail, and then declines to an acutely rounded tip. The ventral fin originates on the body wall and is highest at midlength of the tail. The oral disc is directed anteroventrally. Deep lateral folds are present, and the median half of the anterior labium is bare; elsewhere the labia bear a single irregular row of small, subconical marginal papillae. The jaw sheaths are thin and finely serrate; the anterior sheath is in the form of a broad arch, and the posterior sheath is broadly V-shaped. The labial tooth row formula is 2/3; all rows of teeth are about equal in length, In life, the body is olive brown; the belly is creamy gray, and the tail is tan with olive flecks and brown spots or reticulations. Recently metamorphosed young with SVLs of 10.8–14.1 mm have the incipient color pattern of the adults.

Hyloxalus idiomelus is known from elevations of 1620–2840 m in humid montane forest in the northern part of the Cordillera Central in northern Peru. Individuals occur in spring seepages and along small streams. Free-swimming tadpoles inhabit slow-moving, even marshy, streams. On the eastern slopes of the Cordillera Central, H. idiomelus occurs sympatrically with H. aeruginosus at 2180 m, and with H. mittermeieri at 1620 m.

Males transport 7–12 tadpoles at a time.

Hyloxalus idiomelus (Rivero's rocket frog) is a species of frogs in the family Dendrobatidae. It is endemic to the northern part of the Cordillera Central of northern Peru.