New species of Microhyla from Sarawak: Old World’s smallest frogs crawl out of miniature pitcher plants on Borneo (Amphibia: Anura: Microhylidae)

Abstract

A new diminutive species of microhylid frog (genus Microhyla) is described from the Matang Range, Sarawak, Malaysian Borneo. The new species is an obligate of the pitcher plant, Nepenthes ampullaria, breeding in senescent or mature pitchers, and is Old World’s smallest frog and one of the world's tiniest: adult males range between SVL 10.6– 12.8 mm (n = 8). The new species is diagnosable from congeners in showing dorsum with low tubercles that are relatively more distinct on flanks; a weak, broken, mid-vertebral ridge, starting from forehead and continuing along body; no dermal fold across forehead; tympanic membrane and tympanic annulus absent; Finger I reduced to a nub proximal to Finger II in males; toe tips weakly dilated; phalanges with longitudinal grooves, forming two scale-like structures; webbing on toe IV basal; toes with narrow dermal fringes; inner and outer metatarsal tubercles present; and dorsum brown with an hour-glass shaped mark on scapular region. Miniaturization and reduced webbing may be the result of navigation on the slippery zone of pitchers, situated below the peristome.