Austruca perplexa was formerly in the genus Uca, but in 2016 it was placed in the genus Austruca, a former subgenus of Uca.[4][5][6]
As in other fiddler crabs, the male has a greatly enlarged claw, which is used for signalling. The higher the claw is waved by the male, the greater his chance of attracting a female; the size of the claw is therefore subject to sexual selection.[7] Furthermore, larger male fiddler crabs wave their claws at a faster rate than smaller fiddler crabs to attract larger females. Larger females are more desirable because they produce more eggs than smaller females.[8]
Austruca perplexa is usually found on sandy substrates near river mouths or on sheltered beaches in the mid-intertidal zone, usually near mangroves.[9]