Squid belong to a class of mollusks known as cephalopods, which comprises around 304 species. All squid have eight arms arranged in pairs and two, usually longer, tentacles. They are strong swimmers and certain species can actually "fly" for short distances out of the water. Squid species range in size from a few inches to over 40 feet (12 meters) in length. Some species have the ability to change colors using special pigment-containing cells known as chromatophores. They use this ability for camouflage and ti attract mates.