Which of the following is a common characteristic of squids?

Squids belong to the class Cephalopoda, which makes "cephalopods" the correct choice. This classification includes not only squids but also octopuses and cuttlefish, and they are known for their advanced nervous systems, complex behaviors, and unique anatomy, which includes a head, a set of arms or tentacles, and a distinct body structure. Squids have a soft body that is characterized by a reduced internal shell called a pen, but they do not possess a rigid skeleton like vertebrates do.

In contrast to the other given options, squids are not chordates, which are animals that possess a notochord at some stage of development, such as fish and mammals. They do not have a rigid skeleton, as their bodies are flexible, allowing them to move swiftly in water. Additionally, squids are aquatic creatures, primarily inhabiting oceans and seas, rather than living exclusively on land. Hence, the defining characteristic of squids aligns with them being cephalopods, highlighting their unique evolutionary adaptations to marine life.