Knudsen's Thin-toed Frog

Usual adult snout–vent lengths range between 94–170 mm (3.7–6.7 in) for males and 102.7–154 mm (4.04–6.06 in) for females. They have smooth bodies and wide heads, are orange-brown or greenish on top and have a white belly. They have triangular dark markings on their lips, light-colored lines above the lips, black lines from the nose going over each eye, markings between the eyes.The iris of the eye has a bronze coloration. Juveniles have yellow coloration on their heads. The frogs have only been observed to reproduce in primary forest, where eggs are placed in foam nests and hatched tadpoles swim in shallow pools of water. They are usually found calling next to ephemeral or semi-ephemeral bodies of water.

L. knudseni is native to the greater Amazon basin, being found in Brazil, Bolivia, Colombia, Ecuador, French Guiana, Guyana, Peru, Suriname and Venezuela. A specimen was collected on the island of Trinidad in 1915, but the species current status on the island is unknown.