Arkshells are a group of bivalve molluscs in the family Arcidae, similar to cockles and recognised by thick, ribbed, boat- or ark-shaped shells. Europeans and Asians harvest several edible species — among them Scapharca subcrenata, Arca noae and Anadara broughtoni — prized for sweet, firm meat. Blood cockles of the genus Anadara are unusual among bivalves in containing haemoglobin, which gives their flesh a red colour. Like all filter-feeding shellfish, arkshells can accumulate marine biotoxins, pathogenic bacteria, and viruses from their growing waters, so they must be harvested from classified, monitored areas, depurated where required, and cooked thoroughly before eating.