DISTINGUISHING FEATURES AND BEHAVIORS

Of all the animals that inhabit the nektonic zone, only one invertebrate is a strong enough swimmer to be included in this group. Although squid are among the most advanced and complex mollusks, they lack an external hard shell common to this group of invertebrates.

The long, flattened fins and tube-shaped body of the long-finned squid help it to move gracefully and swiftly through the water. The squid has an aerodynamic body shape and is the fastest swimming of all the invertebrates. Squid move via a system of jet propulsion, filling their bodies with water, moving backwards with arms trailing behind. They can travel for long distances and are often found in schools.

Large, highly advanced eyes, similar in structure to the human eye, detect images and are used to locate prey. The squid has four pairs of arms and one pair of long tentacles with disk-shaped suckers used to grasp its prey. Rather than sticking like a suction cup, each "sucker" has a small barb that grasps onto the skin. When feeding, the squid uses its two longest tentacles to capture the prey, and the shorter arms help it to hold onto the catch. The mouth of the squid looks like a bird's beak. The arms hold the fish near its mouth while the squid uses the beak to eat. Squid feed on fish, shrimp, and other crustaceans.

Squid have speckles along the body that are special pigment cells known as chromatophores. When these cells enlarge, colored splotches are visible and can change according to the squid's behavior. This creature defends itself from predators in several ways. One method is to change into a warning coloration, pulsating purple. Another method is to squirt dark, purplish blank ink, which acts as a screen to blind predators, such as sea bass, bluefish and mackerel.

Female, long-finned squid lay gelantinous masses of eggs on the bottom; the eggs develop directly into embryos. Examining the egg masses under a microscope often reveals a developing and quite active embryo. The eggs aggregrate in the water and are often mistaken for jellyfish. After spawning, the adult squid die.

RELATIONSHIP TO PEOPLE

Long-finned squid are fished commercially and are used for bait as well as for food. The popular Italian dish calamari is made from the arms, tentacles, and body of the squid.