It used to be that the least popular creature in the fishmonger's case was the squid. A recent surge of popularity has removed the stigma attached to the squid so that today the bottom rung is occupied by its close cousin, the octopus. Both are cephalopods, shellfish that through thousands of years of evolution have internalized their hard outer shells. In the case of the octopus, all that remains is its small beak or mouth.
The octopus is an extremely intelligent invertebrate. Jacques Cousteau has shown that it is capable of learning to distinguish colors. Its feeding habits show a sense of acuity as well. Octopuses are fond of crawling into lobster traps, where they eat the bait--shellfish and fish delicacies. This habit makes their meat delicious if people can just get beyond their appearance.
Small octopuses are sold whole. Larger ones are usually sold in pieces, often a leg. To clean a whole octopus, cut around the hard beak, severing the muscles that hold in the viscera. Turn the body cavity inside out and scrape away the viscera. Save the black ink sac, if you like. The ink is somewhat salty and enriches sauces deliciously.
The best way to tenderize an octopus, other than pounding it, which is a lot of work, is to blanch it twice, each time for five seconds with a three- to four-minute resting period in between. After precooking octopus, it can be eaten as is in sashimi or ceviche, grilled, stewed in a rich sauce with red wine and tomatoes, or sauteed with garlic and herbs and added to paella.