Why squid, though not fish, may be better understood by pretending they are

Size is the single most important biological attribute of organisms, and it is the interplay of body mass and some limiting surface which determines the maximum size organisms can reach. In animals, the limiting surface depends, among other things, on whether they are terrestrial or aquatic, so breathing in air or water. In squid, fish and other water breathers, the limiting surface is that controlling respiration, i.e. gill surface area. A theory constructed from this is then presented along with six of its major corollaries, which are shown to be corroborated by available evidence. The key implication of the theory so articulated is that comparative approaches, such as used to infer or check the values of vital statistics in fish, should also work in squid. Also, current, very low estimates of longevity in large squid should be revised upwards.