[Octopus; Pulpo (Spanish); Tako (Japan); Order Octopoda]
Octopi are an order of large mollusks that have evolved entirely out
of their shell. They are related to squid, cuttlefish, the nautilus (which
still has it's shell) and the extinct ammonites only at the Class level
- each of these is in it's own Order. These mollusks are no snails. They
are very intelligent, strong and can move quickly as a recent video of an
octopus capturing a shark for lunch shows.
Octopus has always been a favorite seafood in Italy, Greece and Japan but is known most to Americans as slices of tentacle on top of sushi rice.
Octopi like to hide which makes them fairly easy to catch. Clay jars are dropped on the sea floor to become octopus hiding "caves", then are pulled up with their occupant inside.
Octopus is not marketed by variety, at least not around here, only by size. The sizes most common in Southern California markets are "large", about 2 to 4 pounds and "baby" which may range from 0.1 ounce to 3 ounces.
Octopi around 4 pounds are also sold pre-cooked, generally cut to the weight you order. Uncooked, all sizes are usually sold with the head on but with innards, eyes and beak removed. The "baby" are sold by bulk weight, usually out of a pan where they are mixed with ice to keep them chilled. The larger are tightly bagged in transparent plastic, displayed head side down, and may be still frozen.
It is better to buy octopus that has been frozen because the freezing tenderizes them some and they will cook faster.
While every bit of the octopus you buy is edible, it looses a lot of water when it cooks and will shrink very significantly. While "baby" octopi may yield over 40% of their original weight, large octopi will yield about 30%, or if you cook long enough and rub off the skin and sucker disks it'll be more like 20%.
Since Octopus is generally sold "cleaned" (beak, eyes and innards removed) there's no cleaning required and yield is just about 100% - of the solids. You're going to take a huge hit on weight because so much of an octopus is water and that gets squeezed out in the first few minutes of cooking. See the separate sub-articles for details on cooking octopi of different sizes.
Octopus gets an "A" grade for nutrition: very low fat, high in niacin, phosphorus, potassium, vitamin B6 and zinc; very high in iron, selenium and vitamin B12. The only negatives are sodium and cholesterol. Since it's been found very few people absorb significant cholesterol from food (it's manufactured within the body) this last is not a particularly serious point.