(pronounced ark-ee-TOO-this) Architeuthis is the giant squid. It is the largest squid and the largest invertebrate (animal without a backbone), but it has never been seen since it lives very deep in the oceans. The largest-known Architeuthis was 57 feet (17.5 m) long. It has eight arms, two longer feeding tentacles, a beak, a large head, and two eyes larger than basketballs! These soft-bodied cephalopods are fast-moving carnivores that catch prey with their tentacles, then poison it with a bite from beak-like jaws. They move by squirting water through a siphon, a type of jet propulsion. Only dead examples of Architeuthis have been found. Its only enemy is the sperm whale who hunts it deep in the ocean.

Giant squid, once believed to be mythical creatures, are squid of the Architeuthidae family, represented by as many as eight species of the genus Architeuthis. They are deep-ocean dwelling animals that can grow to a tremendous size: recent estimates put the maximum size at 10 m (33 ft) for males and 13 m (43 ft) for females from caudal fin to the tip of the two long tentacles (second only to the colossal squid at an estimated 14 m (46 ft), one of the largest living organisms). The mantle length is only about 2 m (7 ft) in length (more for females, less for males), and the length of the squid excluding its tentacles is about 5 m (16 ft).