Extant and ancient cephalopods—including octopuses, squids, extinct ammonites, cuttlefish and nautiluses—have all had to solve the problem of buoyancy, whether they have hard external shells or not.

Source: Princeton University Press/ Used with permission. Octopuses and other cephalopods are amazing, strange, sentient beings. They have very active social lives and brains—some say octopuses have ...