Osteocephalus castaneicola Moravec, Aparicio, Guerrero-Reinhard, Calderón, Jungfer & Gvozdík 2009

Diagnosis: Can be distinguished by the following combination of characters: (1) medium size (adults reaching 47.8-51.3 mm SVL in males, 47.7-63.3 mm SVL in females); (2) snout rounded in both dorsal and lateral view; (3) distinct, angular, medially curved canthus rostralis; concave loreal region; (4) low frontoparietal ridges; (5) large rounded (or oval) tympanum; distinct tympanic annulus; well-developed supratympanic fold; (6) in males, vocal sac indistinct, vocal slits lacking; (7) vomerine dentigerous processes are large, angular and located between obliquely oriented choanae; dentigerous processes have 6-14 vomerine teeth each and may be narrowly separated or contacting each other; (8) tuberculate dorsum; (9) small, low tarsal and ulnar tubercles are present; these are slightly larger than the minute dorsal tubercles; (10) no axillary membrane; (11) fingers basally webbed; toes 3/4 webbed; (12) Finger IV with single round distal subarticular tubercle; (13) nuptial excrescences are dark and keratinous and restricted to the prepollex; (14) adult coloration in life: dorsum brown (tan to purplish brown) with a few irregular darker brown markings; pale lip stripe expands to a subocular spot; flanks pale and unmarked; concealed thigh surfaces light brown; throat and belly white; narrow dark stripe along lower jaw; thighs fleshy pink ventrally; bicolored iris with golden upper half, dark dividing stripe, bronze lower half, all with fine dark reticulation; tibia green or white; (15) metamorph coloration in life: light brown dorsum; darker interorbital spot; white upper arms, knees and heels; iris bright orange (Moravec et al. 2009). Description: Adult males measure 47.8-51.3 mm SVL. Adult females measure 47.7-63.3 mm SVL. Head slightly longer than wide. Snout rounded with distinct medially curved canthus rostralis, concave loreal region and slightly depressed internarial region. Nostrils are slightly protuberant. Eyes are large and quite protuberant. Frontoparietal ridges are present. Large rounded tympanum with distinct annular ring and a well-developed supratympanic fold obscuring the dorsal edge of the tympanum. Vomerine ridges are angular, large and prominent with 6-14 teeth each. Tongue ovoid and widely attached to bottom of mouth. Arms are slender. No axillary membrane is present. Forearm has small low tubercles on the ventrolateral edge. Fingers are basally webbed and have expanded oval discs. Finger III disc width equals about half the diameter of the tympanum. Subarticular tubercles are single, and round. Supernumerary tubercles are present. Palmar tubercle is large and flat. Prepollical tubercle is elliptical and flattened. Legs are moderately long and slender. Heels overlap when limbs are adpressed. Toes are moderately long with oval discs, and are three-fourths webbed. Toe discs are slightly smaller than finger discs. Subarticular tubercles are single, protuberant, and rounded; supernumerary tubercles are also present. Tibiotarsal articulation has small raised tubercles on the outer edge. Posterior surface of proximal third of thigh has rounded tubercles. Ventrolateral edge of foot has small low tubercles. Outer metatarsal tubercle is distinct, round, and small; inner metatarsal tubercle is large and ovoid. Short cloacal sheath present. Vent surrounded by rounded tubercles. Skin on dorsum, head, and dorsal limbs with minute tubercles. Flanks are shagreened. Venter has coarse granulation. Males lack vocal slits and have an indistinct vocal sac. Nuptial pads are dark and keratinous and are confined to the enlarged prepollex (Moravec et al. 2009).Coloration is pale brown to purplish-brown with occasional irregular dark brown markings. A light narrow stripe runs on the upper lip, expanding into a spot underneath the eye. A dark narrow stripe runs along the lower jaw. Throat and belly are creamy white. Flanks are light colored. Hidden surfaces of thighs are light brown and the undersurfaces of the thighs are fleshy pink. Tibiae are green or white. Iris has fine dark reticulation over a golden upper half, a dark medial stripe, and a bronze lower half (Moravec et al. 2009).Newly metamorphosed juveniles are light brown with a dark interorbital spot. Bright orange iris. Upper arms, knees and heels are creamy white. (Moravec et al. 2009).The specific name castaneicola derives from the Spanish word castaña, for Brazil nut tree, and the Latin word colō, meaning "to inhabit" (Moravec et al. 2009).

Occurs in Bolivia and possibly adjacent southern Peru. Found in the southwestern Amazon basin, in the western and central part of Departamento Pando, northern Bolivia, from 200-270 m asl (Moravec et al. 2009). It apparently occurs in the Region Madre de Dios of adjacent southern Peru (listed as Osteocephalus sp. by von May et al. 2007, who did not provide specific localities), but this needs to be confirmed. The habitat is undisturbed tall evergreen lowland Amazonian rainforest, with a dense canopy that is 25-35 m above the ground, well-defined tree strata, frequent large trees of various species, and an extensive understory consisting of tree seedlings and young trees, herbaceous lianas, ferns, and palms (Moravec et al. 2009). The forest floor has leaf litter and large fruit capsules of Brazil nut trees (Bertholletia excelsa) as well as fruit capsules from other Lecythiadaceae (Moravec et al. 2009).

Individuals perch on vegetation 0.5-2 m above the ground. No calls were heard, but tadpoles were found in water-filled Brazil nut fruit capsules. Fruit capsules are opened by humans (indigenous Brazil nut collectors) or by agoutis (Dasyproctis sp.). Breeding in fruit capsules provides protection and stable water conditions for the tadpoles, as water remained in the capsules much longer than it did in temporary puddles on the forest floor. Some capsules were found to contain tadpole assemblages of tens of individuals. Very occasionally O. castaneicola tadpoles were also found in water-filled palm bracts on the ground (tadpoles were collected and raised to metamorphosis, then compared genetically with adult specimens). The larvae in assemblages are of various sizes and various stages of development. This species appears to have at least female parental care, as white ingested eggs were sometimes visible through the transparent venters of larger larvae (Moravec et al. 2009).This species represents the first hylid known to use Brazil nut fruit capsules for breeding. Other frog species using these capsules for breeding include Dendrobates castaneoticus (a dendrobatid), Dendrobates quinquevittatus (also a dendrobatid), and Bufo castaneotica (a bufonid) (Caldwell 1993; Lötters et al. 2007). Like O. castaneicola, B. castaneotica also occasionally makes use of alternative breeding sites, namely small water-filled holes in the soil (Köhler and Lötters 1999).

Osteocephalus castaneicola is a species of frog in the family Hylidae. It is found in lowland Amazonia of northern Bolivia, adjacent southeastern Peru, and western Brazil (Acre, south-central Amazonas, and Rondônia). It breeds in water-filled fruit capsules of the Brazil nut, a characteristic also alluded to in its specific name castaneicola derived from the Latin castanea (horse chestnut, Aesculus), the root of the vernacular name castaña for the Brazil nut, together with the Latin colō meaning "to inhabit".