Snout long and wide. In dorsal view, broadly rounded with an anterior embayment accommodating the mouthparts. In lateral view, snout tip truncated. Jaws slightly recessed.

Tail comprising approximately 60–65% of total length. Tail moderately developed, narrow in dorsal view relative to body size and much narrower than the trunk. Muscular portion markedly lower than body height in lateral view. Upper fin originating at the trunk-tail junction, rising steeply to form a convex arch in the middle section of the tail, where tail height is greatest. Posteriorly, the contour of the upper fin runs straight or slightly concave toward a narrowly rounded tail tip. Lower fin similar in shape but slightly higher, reaching maximum height slightly anterior to that of the upper fin. In the anterior 25% of the tail, an opaque, heavily pigmented patch is present, covering the muscular portion of the tail and parts of the tail fins; this patch is longer than high and smoothly rounded posteriorly and becomes even more conspicuous in preserved specimens. Skin glands absent. Lateral tail vein not visible. Muscle myosepta discernible only under magnification.

In dorsal view, the combination of a very large, wide head and a weakly developed tail clearly identifies tadpoles of Kaloula as microhylids and distinguishes them from pond-type tadpoles of other frog families in Borneo. Larvae of K. baleata and Kaloula pulchra are similar, and diagnostic features have not been established with certainty. We observed an opaque patch in the anterior third of the tail in K. baleata—a feature otherwise known from Polypedates—that was absent in K. pulchra, representing a potential distinguishing character. In addition, the sharp-edged orange-yellow flecks characteristic of K. baleata appear to be absent in K. pulchra tadpoles.

Adults congregate after heavy rainfalls at forest ponds but also at ponds at forest edges or clearings. Males usually call from hidden spots such as in vegetation or in hollow logs. The deep, forceful voice of the males gave them the name bullfrog. An amplecting pair can lay large numbers of eggs and, thus, a pond can be populated by large numbers of these tadpoles.

Iskandar, D.T. (1998). The Amphibians of Java and Bali. Research and Development Centre for BiologyLIPI and GEFBiodiversity Collections Project, Bogor. 117 pp + 26 pl.