Squid (Illex coindeti) swimming forward—Douglas P. Wilson
Any of nearly 400 species of 10-armed cephalopods, found in both coastal and oceanic waters, that prey on fishes and crustaceans. They range from less than 0.75 in. (1.5 cm) to more than 65 ft (20 m) long (in the case of the giant squid). Two of the 10 arms are long, slender tentacles; each has an expanded end and four rows of suckers with toothed, hard-edged rings. An internal shell supports the slender tubular body of most species. Squid eyes, almost as complex as human eyes, are usually set into the sides of the head. Squids may be swift swimmers (propelling themselves by contracting and relaxing their mantle or by undulating their two fins) or mere drifters; water expelled from a funnel below the head can propel the squid backward. Like the octopus, the squid may emit an inky cloud from its ink sac when in danger from sperm whales, fishes, or humans, among other predators.