The New York Times, June 18, 2019


The cuttlefish and its relatives, squid and octopuses, often strike human observers as floating aliens wreathed in sucker-covered limbs — boneless, squirming appendages that would seem to have nothing in common with our own arms and legs.

But hidden under the superficial differences, a new study shows, are some profound similarities: Human and cuttlefish limbs develop under the direction of the same genes. The new study, published on Tuesday in the journal eLife, lends weight to the theory that many animal appendages, from insect wings to fish fins, share a long evolutionary history.

Cuttlefish, squid and octopuses are all cephalopods, a group that evolved over 400 million years ago from a mollusk ancestor. Later, cephalopods evolved appendages in two forms.

An octopus has eight appendages, each of which has rows of suckers running its length. But these are not tentacles — in strict anatomical terms, they are arms. A tentacle has suckers only on its pad-shaped ending. Squid and cuttlefish have arms, but also tentacles.