Description

 Carapace broader than it is long (up to 3 cm across), with 5 sharp unequally sized antero-lateral teeth on each side. Frontal region very finely serrated between the eyes. Carapace and all walking legs densely covered with club-shaped setae. Chelipeds stout and robust, one (usually the right) much larger than other, and brownish or purple in colour with orange to cream inner surfaces. Carapace reddish-brown, sometimes purplish in colour. Walking legs with alternate bands of purple and white or grey.Dorsal surface of carapace bears short spines beneath the setae; clearly evident in young specimens but increasingly hidden by hairs in older crabs. Silt often accumulates among setae making Pilumnus hirtellus difficult to see on dark or silty surfaces.