Squid

The Squid is a fish that can be found in the ocean between December and mid-August, at any time of the day. Despite it being called a fish in, it is infact a type of mollusc (Europe) / mollusk (US) , like (but not directly related to) the Octopus.

Encyclopedia Information
Once the player has caught a particular fish or bug, they can find information about it in the bug or fish menus. Once the squid has been caught, the following information can be found in the fish menu:

Wild World

 * Size: 13.7 inches
 * Habitat: Ocean
 * Season: Winter to summer
 * Eight of its ten appendages are arms, and the other two are tentacles.

City Folk

 * Size: 14 inches
 * Habitat: Ocean
 * Season: Winter to Summer
 * Eight of the tentacles are legs--the two longer ones are actually arms.

Further Information
The type of squid in Animal Crossing isn't mentioned, but judging by the in-built City Folk description, it maybe a European Squid which is white with two long arms. The family name,  'Loliginidae'  is commonly refered to as the inshore, calamari, and grass squid. Squid eat small plants, insects and small animals that float on the surface of the ocean.