Hylarana (Chalcorana) megalonesa was described by Inger et al. (2009) from the type locality at Bukit Sarang, Sarawak. The species is also known from Sabah and is very likely to be found in parts of Kalimantan.

H. megalonesa is very similar in coloration and overall body shape to the closely related Hylarana (Chalcorana) raniceps. However, H. megalonesa is significantly larger (*females* >50 mm, *males* >35 mm snout–vent length) and exhibits more dark spots on the dorsal surface (dorsum). Both species are clearly distinguishable by genetic analysis.

H. megalonesa is mostly green but often features a broad brown mid-dorsal band extending from the snout and head over the back to the vent. The snout is long and pointed, giving the head a triangular shape when viewed from above. The finger and toe tips bear well-developed adhesive disks.

Apart from H. raniceps, H. megalonesa could potentially be confused with Odorrana hosii. However, O. hosii differs from H. megalonesa, notably by the absence of an outer metatarsal tubercle.

H. megalonesa reproduces in ponds, intermittent streams, or quiet side pools of streams. Since this newly described species has only been distinguished from H. raniceps based on molecular data and adult morphology, its tadpoles’ distinguishing characteristics remain unknown—tadpoles of both species are very similar. More research is needed to clarify this.