Cephalopods refer to a large and diverse group of marine animals characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles. This category includes species such as squids and octopuses, and falls under the larger category of mollusks, which also includes animals like bivalves. Despite living in the same aquatic environment as amphibians, cephalopods are not related to them and represent a separate category within the animal kingdom.