Cuttlefish are mollusks of the class Cephalopoda which also includes nautili, squids and octopods. The class as a whole is adapted for a swimming exstence and contains the most specialized and highly organized of all mollusks. Cuttlefish swim by rapidly expelling water from their mantle (body) cavity. Water is inhaled then forced to leave through a tubular funnel. The force of the water leaving the funnel propels the animal in the opposite direction. The funnel is highly mobile and can be directed anteriorly or posteriorly, resulting in either forward of backward movement. The rapidity of movement depends largely on the force with which water is expelled from the funnel, but movements are beautifully controlled. The fastest movement is achieved in backward escape swimming, when powerful contractions of the mantle eject water from the anteriorly directed funnel.
Squids and cuttlefish are the best adapted mollusks for swimming by water jet. Cuttlefish are slower swimmers than the more streamlined squids. As in squids, the fins in cuttlefish function as stabilizers, but they undulate and are also used for steering and propulsion.
The shell of cuttlefish, despite its evolutionary reduction, still functions in providing buoyancy for the animal. Spaces between the thin septa contain fluid and gas, mostly nitrogen. By regulating the relative amounts of fluid and gas, the degree of buoyancy can be varied. Light is an important factor controlling the regulating mechanism. During the day the cuttlefish lies buried in the bottom; at night the animal becomes active, swimming and hunting for food. Buoyancy decreases when the animal is exposed to light and increases in the dark.
Cuttlefish are highly adapted for raptorial feeding and a carnivorous diet. Prey is located with highly developed eyes, which are strikingly similar in structure to those of vertebrates, and capture is effected by the tentacles and arms.
Cuttlefish possess ten arms arranged in five pairs around the head. Eight are short and heavy and are called arms; two are twice the length of the arms and are called tenticles. The inner surface of each arm is flattened and covered with stalked, cup-shaped adhesive discs that function like suction cups. Suckers are present only on the flattened spatulate ends of the longer tenticles.The highly mobile tenticles are shot out rapidly to seize the prey, which is then drawn toward the mouth; the arms aid in holding the prey. Cuttlefish swim along the sea bottom and feed upon invertebrates, especially shrimp and crabs.
The principal enemies of cuttlefish are fish and whales. The same species (such as mackerel) that when young served as food for the cuttlefish, may in adult life prey on the cuttlefish.
Reference: Invertebrate Zoology by Robert D. Barnes, Ph.D.
