Larvae of Portunus acuminatus (Stimpson, 1871) from one female, collected by trawling at a depth of 12 m in the Gulf of Nicoya, Pacific Costa Rica, Central America (090°48.899’N, 084°40.498’W) were hatched in the laboratory. The morphology of zoea I is described and illustrated for the first time and compared with known zoeae of other portunid species belonging to the subfamily Portuninae. We present a combination of three features which allows zoea I larvae of P. acuminatus to be distinguished from other described larvae of the genus. Descriptions are based on dissected larvae analysed by SEM and light microscopy.