Comprehensive DescriptionRead full entry
Atelopus arthuri is an ignescens frog with a snout vent length of approximately 46.9 mm. From above the fleshy snout appears pointed and from it appears to protrude beyond the upper lip and lower jaw, with the nostril directed laterally and slightly posteriorly. The muzzle also appears to be concave between the canthi. The canthus and upper eyelids are also fleshy and a fleshy fold extends from the corner of the posterior corner of the eye to the end of the head. The tympanic and temporal regions are granular. The dorsum of the body varies between noticeably smooth or finely wrinkled, and lacks pustules. Conversely the sides of the body, as well as most of the upper surfaces on the limbs are very pustulate. Females will have whitish spinules either individually or clustered together atop these pustules. Ventral surfaces tend to be smooth and without pustules but can also be wrinkled. The forelimbs are very short. The forearms are slightly larger in diameter than humeral regions. The forefeet are fleshy and webbed. The hind limb is short and fleshy with fleshy webbed feet extending up to the first phalange of each digit. Hind limbs are also short, fleshy, and webbed. Webbing extends to the tips of all but the fourth toe. The sole of the foot is smooth (Peters 1973).
In life, dorsally Atelopus arthuri is light to dark brown and dark brown pattern with heavy reticulations of orange-yellow on both body and limbs. The sides are reversed, with a dull reddish orange background and brown reticulations. The ventral surfaces of the thighs, chest, and belly have a tomato red spot surrounded by green. Some individuals have been found with a brown patch on the buttocks and a brownish spotting on the chin and throat. Soles and palms are dull orange. The pupil is black surrounded by a bright green ring and a black iris with minute green spots. In alcohol the dorsum, sides, and limbs are a light grayish brown color with some darker brown spotting or streaks. Sides also have white spots on the tips of the pustules. Some individuals have clear, colorless limbs with yellow on the first two digits and webbing. The chest, the belly, and the ventral surfaces of the thighs and humerus are light yellow color allowing transparency into the abdominal cavity. Ventral surfaces of limbs is dark brown with puncated yellow, while the hands and feet are completely yellow to brown. A large brown patch is present on the thighs below the vent extending on to the ventrum. The chin and throat are yellow with brown spotting or streaking (Peters 1973).
Individual Atelopus arthuri are noted to be very different from each other in how their colors are distributed on their body. In addition the actual patterns and colors themselves are more or less unique to each frog (Peters 1973).
The name of the species is derived from the first name of the person who collected the holotype (Peters 1973).