Haikouichthys (SciiFii)

Haikouichthys modernus is a basal chordate that originally lived during the Cambrian as an extinct species of Haikouichthys and the genus itself was originally extinct, but has since been recreated by SciiFii and sold as aquarium pets. They are carnivores, and thrive in captivity. They live in groups of up to 30 in a sufficiently large aquarium, but when space is limited, they behave aggressively towards one another, often cannibalising one another.