Key to species of the Macrobrachium placidulum species group

1. Rostrum with 3 or 4 postorbital teeth and epigastric length 0.23–0.27 of carapace length.............. M. ngankeeae n. sp.

– Rostrum with 4–7 postorbital teeth and epigastric length 0.24–0.55 of carapace length............................... 2

2. Rostral dorsal margin above eyes flat and straight................................................... M. feunteuni

– Rostral dorsal margin above eyes convex.................................................................. 3

3. Ocular beak absent or very poorly developed.................................................... M. placidulum

– Ocular beak well developed............................................................................. 4

4. T4 without median process..................................................................... M. placidum

– T4 with median process.................................................................. M. lepidactyloides