Percnon planissimum  

Carapace nearly subcircular (slightly longer than broad) and flattened with smooth dorsal surface covered with small setae. Anterolateral with three teeth. Frontal margin characterized by a pair of distinctive clefts. Dorsal margin of pereiopod merus with spines.

Vernacular name: Reef surf crab.

These crabs reside in subtidal areas with very strong currents or places with strong surfs. To ensure they are not washed away, they have long powerful legs lined with spines to improve their grip and flat carapaces to reduce drag. They are mostly algivores.