Crustaceans, including crabs, lobsters, shrimps, and barnacles, are for most part available all year, but are consumed rather occasionally by most coastal cultures.
Crustaceans include well-known decapods (crabs, lobsters, and shrimps), but also amphipods (skeleton shrimps) and sessile barnacles. All decapods have tough shield-like plates (exoskeleton) covering each of their body segments and those plates are fused and reinforced into a well-developed carapace enclosing the head and thorax (cephalothorax). Because of their tough exoskeleton and carapace, most decopds grow through out their lives via stepwise series of molts and secretion of a new exoskeleton. Decapods have stalked eyes and five pairs of well-developed and jointed walking legs, the first of which is modified into large pincers with one being much bigger than the other. Barnacles are permanently attached to the substrate and secrete a calcareous shell resembling that of bivalves.
Reference
Rainbow PS: "Crabs, Lobsters, Shrimps, and Allies". In: The Encyclopedia of Underwater Life. Edited by Dawes ACJ: Oxford University Press; 2007.