Squid

Squid are passive mobs. They were added in the Minecraft Beta 1.2 update. Squid are found in water, and drop ink sacks when killed. They spawn on any difficulty and do not attack, akin to the other passive mobs found on land.

Behavior
Squid swim around in water, sometimes in groups and stick to the seabed, swimming into sand/dirt on the seabed quite often. When they bump into a block, they make the same sound as land-walking mobs. They often swim fairly deep, and are difficult to see due to their dark complexion, and, unless seen from a distance, are almost impossible to locate from above. When they move about, their arms open and close. This is the easiest thing to watch for in the deeper areas when squid hunting. Squid will not attack you, even when you attack them.

Captured Squid : http://www.youtube.com/watch?v=mPAQYjGcFRU

Drops

 * 1-3 ink sacks

Trivia

 * It is impossible to pull a squid onto land with a fishing rod.
 * Can be found above ground in water of any depth.
 * Can be found in pools as shallow as 1 block, or 2 underground. The pool needs to be at least 2 wide, though.
 * Are immobile when on land, and eventually suffocate.
 * Have 8 arms. (Real squid have 8 arms and 2 tentacles. )
 * Can end up above water, and swim through the air, due to a bug.
 * Squid are affected by Flint and Steel (Only when above water, though).
 * Squid cannot swim upwards and sink in water, making them extremely easy to trap.
 * It seems that hitting a squid underwater causes them to rise approximately 1/3 to 1/2 a block.

Videos
A squid out of water: http://www.youtube.com/watch?v=vqgWWRpP2Hw