Appearance
Their rather flat and smooth carapace is usually wider than long and of hexagonal, subhexagonal, rectangular, or transversely ovate shape. It is usually widest between the hindmost spines of the forward rim; there may be up to 9 pairs of these spines, with a few smaller ones right above the head, but they are missing altogether in some species.
In some, the first maxilliped's endopod is lobed, forming the characteristic portunid lobe. The chelipeds are usually robust, and in some the last pereiopod pair has ovate dactyls. The sutures of the sternum between segments 4 to 8 are usually incomplete, and in the Portunidae, the eighth sternite is usually visible if seen from below and has a penial groove.