Adelophryne gutturosa is a minute frog originally described from one male, one female, and one juvenile specimen, but supplemented with several more specimens over the next two decades. The snout-vent length of females ranges from 12.4 – 16 mm, while the males have snout-vent length between 12.6 – 15 mm (Hoogmoed and Lescure 1984, Hoogmoed et al. 1994, MacCulloch et al. 2008). The head is a bit longer than wide, and is somewhat wider than the body. From the lateral and dorsal profile, the snout is truncated with the tip of the snout having an obtuse median point. The lips are flat and do not flare. The indistinct canthus rostralis is straight and rounded. The laterally directed nostrils are vertically oval, do not project, and are surrounded by a translucent area. The loreal region slopes sharply to the upper lips. The internarial distance is somewhat smaller than the interorbital distance. The eye has a horizontally oval pupil. The slightly convex eyelid is a third the length of the interorbital distance. The eye diameter is the same length as the distance between the nostril and the eye, and that distance is approximately equal to or slightly greater than the distance from the nostril to the tip of the snout. The temporal region is vertical. The small but distinguishable, tympanum is round and about a third the diameter of the eye. It is encompassed by a well-defined, incomplete tympanic annulus that is covered at the top with skin. The tympanic diameter is equivalent to the distance between the tympanum and the eye. Females have a horizontal supratympanic fold that is absent in males. All individuals in this species have a skin fold connecting the corner of their mouth to bottom edge of the tympanum. They also have an indistinct granular ridge leading from the middle of the tympanum in a straight line to the insertion of the arm (Hoogmoed and Lescure 1984, Hoogmoed et al. 1994).
The male vocal sac is subgular and distinguished by two longitudinal folds on the sides of the throat and one curved fold at the anterior of the insertion of the forelimbs (Hoogmoed et al. 1994). The skin texture of the dorsum is smooth, or shagreened, while the skin on the temporal region, flanks, and posteroventral region of the thighs is granular (MacCulloch et al. 2008). The skin on the limbs and ventrum is smooth. The skin on the throat of males is wrinkled. Discoidal folds are not present in this species (Hoogmoed and Lescure 1984).
The outer metacarpal tubercle is large, undivided, irregularly shaped and flat. The inner metacarpal tubercle is smaller than the outer, oval, and flat. At the base of fingers II, III, and IV there are indistinct, flat, and oval supernumerary palmar tubercles. Under each phalange, there is a single large, oval, flat subdigital pad, except for the third, which has two. The fingers are depressed, unwebbed, and have narrow, transparent lateral fringes. The fingertips are asymmetrically pointed and do not have discs or circumferential grooves. The relative finger lengths in the original description are I < II < IV < III, however some specimens have longer or equal length finger IV compared to finger II (Hoogmoed and Lescure 1984, Hoogmoed et al. 1994).
The tibia is 45 – 53 % of the snout-vent length. When adpressed to the body, the heel reaches the nostril. When held at 90-degree angles to the sagittal plane, the heels of the hindlimbs moderately overlap (Hoogmoed and Lescure 1984). The shanks are 45 - 52% of the snout-vent length (MacCulloch et al. 2008). The tarsus does not have a ridge or tubercles. The inner metatarsal tubercle is large, oval, flat and distinct. The outer metatarsal tubercle is smaller than the inner (about half the size), round, and conical-shaped (Hoogmoed and Lescure 1984). Like the hands, the toes have indistinct subdigital pads at the base of the toes that are flat and oval, but more prominent than the pads on the hands. There is one pad on toes I and II, two on toes III and V, and three on toe IV (Hoogmoed et al. 1994). The feet do not have supernumerary tubercles. The depressed, unwebbed toes are have a relative toe length of I < II < V < III < IV. Like the fingers, the toes have narrow, transparent lateral fringes. The tips of toes I - IV expand into small, narrow discs that are only marginally wider than the toes and end with asymmetrical pointed tips. The discs have a circumferential groove that has a narrow interruption at the tip. Toetip V is more rounded and barely has a discs (Hoogmoed and Lescure 1984, Hoogmoed et al. 1994).
One juvenile had a snout-vent length of 13 mm (Hoogmoed et al. 1984, MacCulloch et al. 2008). The tibia is slightly longer in juveniles than in adults at 51—53% of the snout-vent length (Hoogmoed and Lescure 1984).
Adelophryne gutturosa can be distinguished from most eleutherodactylids by a combination of the number of phalanges it has, digital discs and pads, and skin texture and color. More specifically, the absence of a tarsal tubercle but presence of vomerine teeth distinguishes A. gutturosa from members of the genus Noblella. Having one subdigital pad on Finger IV and males having a distinct subgular vocal, but lacking a fleshy ridge on the snout distinguishes A. gutturosa from Hypodactylus nigrovittatus. Flattened digits with indistinct subdigital pads, a short second phalange of the fourth finger, and a large subgular vocal sac distinguishes A. gutturosa from Phyzelaphryne miriamae (Hoogmoed and Lescure 1984). Having a smooth dorsum, three phalanges instead of two on the fourth finger, a short second phalange of the fourth finger, and the unwebbed portion of the fourth finger being more than half the length of unwebbed portion of the third finger distinguishes A. gutturosa from A. adiastola (Hoogmoed and Lescure 1984, Hoogmoed et al. 1994). Having three phalanges on its fourth finger instead of two further distinguishes A. gutturosa from A. pachydactyla. Having subdigtial pads instead of subarticular tubercles and a tympanum that is approximately the distance of one eye diameter from the eye distinguishes A. gutturosa from A. baturitensis. Having a more truncated snout, narrow digital discs, and a posteriorly opening vent with no flap distinguishes A. gutturosa from A. maranguapensis (Hoogmoed et al. 1994). The lack of an anal flap, along with larger size, presence of digital discs and grooves, and subdigital pad formula, also distinguishes A. gutturosa from A. mucronatus (Lourenço-de-Moraes et al. 2012). Adelophryne gutturosa lives sympatrically with A. patamona but the following characters of A. gutturosa allow researchers to distinguish between the two species (A. patamona characters in parentheses): the second phalange of finger four is short with the length equal to or greater than the width (long, two times its width); the canthus rostralis is straight (concave); there are 2-8 vomerine teeth (15-16); snout vent length is around 16 mm or smaller (larger size around 23 mm). Lastly, the two species’ calls can also be used to distinguish them (MacCulloch et al. 2008).
The coloration of A. gutturosa in life is variable. However, in general, the dorsal and ventral ground color is grey or medium brown with many non-uniform sky blue and/or white dots on the dorsum, ventrum, flanks, and limbs. There may be a black “)(” shape on the dorsum. The canthus rostralis may also be black and there may be supratympanic bars or other scattered marks. The fore- and hindlimbs are medium brown or grey on the dorsal surfaces and may have black crossbands or marks. The upper arm is orange. The flanks and upper region of the thighs may be whiteish with numerous dark stippling but no crossbands. The iris is copper with a red ring surrounding the pupil. In preservative, the ground color remains the same but the orange and sky-blue colors become white (MacCulloch et al. 2008).
There is variation in coloration, patterning, and the length of Fingers II and IV. There are also several features that show sexual dimorphism. Ostologically, the second phalange in finger IV is cubic in males but longer, making a short rectangle in female. In males, the terminal phalanges of fingers I, II and IV are bluntly pointed to knobbed, and finger III is knobbed, where as in females they are T-shaped. This is mirrored in the toes, where the terminal phalanges of males are knobbed but T-shaped in females. Morphologically, females also have a horizontal supratympanic fold that is absent in males (Hoogmoed and Lescure 1984). In preservative, some individuals, potentially sexually dimorphic (in males), may have brown spots along the vertebrate or two incomplete dark brown transverse bands on the shanks (Hoogmoed et al. 1994). The throat of the male is dark brown with small white spots on the anterior, whereas the female’s throat is similar to the belly but only a little darker (Hoogmoed and Lescure 1984, Hoogmoed et al. 1994).
The species authority is: Hoogmoed, M. S., and J. Lescure. 1984. A new genus and two new species of minute leptodactylid frogs from northern South America, with comments upon Phyzelaphryne (Amphibia: Anura: Leptodactylidae). Zoologische Mededelingen 58: 85–115.
Based on Bayesian Inference and Maximum Parsimony analyses of both nuclear and mitochondrial DNA, A. gutturosa is sister to A. adiastola. The clade formed by these species is sister to A. patamona. These species, along with an unnamed species make up the North Amazonia Clade (Fouquet et al. 2012).
Adelophryne comes from the Greek words “adelos” meaning “unseen, unknown, obscure”, and “phryne” meaning “toad” (Hoogmoed and Lescure 1984). The species epithet, “gutturosa” comes from the Latin word “gutturosus”, meaning “with enlarged throat”. This refers the frog’s huge lower part of the throat in adult males’ vocal sacs (Hoogmoed and Lescure 1984).