[4] The specific name segnis means “slow”, “torpid”, “lazy”, “unenergetic”, “tardy” or “inactive”,[5] and Forskål described it as proceeding slowly in water ("tarde procedit in aqua").

[3] Portunus segnis males have a dark olive green blue carapace marked with numerous pale white spots on especially towards the rear and along the sides.

[4] Portunus segnis is found in the western Indian Ocean from the eastern African coast and the Red Sea east to Pakistan and south to Madagascar and Mauritius.

[6] The diet of Portunus segnis is seasonally dependent, with them eating crustaceans such as other crabs and shrimps more prominently in the summer, and fishes and molluscs more common in the autumn and winter.

[7] Although the aforementioned animals form the major part of this species’s diet, studies have identified annelids, cnidarians, plants, and even debris in the stomach of Portunus segnis subjects.

[8] This species is mainly nocturnal[4] and hunts across the surface using a zigzag pattern to find its prey,[6] spending the day buried in the sediment with only its eyes, antennae and gills clear of the substrate.

[4] The epizoic acorn barnacle Chelonibia patula has been collected from the exoskeleton of this species in the eastern Mediterranean Sea.