Octopus

I

Introduction

Octopus, carnivorous marine mollusk, found worldwide in tropical and warm temperate waters. The octopus is characterized by eight limbs of equal length, a soft body, and a well-developed head. The word octopus is from the Greek meaning “eight-footed.”

II

Physical Characteristics of the Octopus

Each limb of the octopus bears one or two rows of suction cups, depending on the species. The limbs are joined at their bases and along part of their length by a web of tissue called the skirt. At the center of the skirt are a horny parrotlike beak and a “tongue” known as the radula. The main body is composed of tissue layers called the mantle.

Octopuses often use their rearmost limbs as legs for pushing off from the sea bed. The remaining six limbs, or arms, are used for feeding and swimming. Octopuses also crawl using all eight limbs. If a limb is lost, it may regenerate (grow back). Larger species of octopuses can measure up to 10 m (33 ft) from arm tip to arm tip while smaller species may measure only 5 cm (2 in) from arm tip to arm tip.

Octopuses have three hearts, one that pumps blood throughout the body and two that pump blood to the gills. Octopus blood is blue in color because the oxygen-binding protein hemocyanin contains copper. (Human blood is red because the oxygen-binding protein hemoglobin contains iron.) Only about one-third of the neurons in the octopus’s nervous system are located in the brain; the remaining two-thirds are located in the limbs. Although the octopus cannot hear, its vision is acute; the two large, complex eyes are cameralike in structure. The senses of smell, taste, and touch are also excellent. Receptors on each suction cup allow the octopus to taste whatever it touches.

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III

Habitat and Behavior of the Octopus

Octopuses live in temperate and tropical seas throughout the world. Most are bottom dwellers in relatively shallow water, but some live at the surface of the open sea and others to depths of 4,500 m (15,000 ft). The octopus spends much of its life in hiding. Many species—such as the common octopus, which measures about 1 m (about 3 ft) from arm tip to arm tip—choose to inhabit a natural lair formed by rocks. A small species—such as the Atlantic pygmy octopus, which measures 10 cm (about 4 in)—may inhabit an empty clamshell. Settling into one half of the shell, the octopus closes it with its suction cups.

Octopuses feed on crabs, snails, fishes, bivalve mollusks, and other marine animals. An octopus will lure a fish by wiggling the tip of an arm like a worm; or it will glide near and pounce on a crab, sinking its beak into the shell and injecting a poison that kills. (The poison of a very few species is dangerous to humans.) Octopuses are preyed upon in turn by a number of fishes, including the moray eel. When threatened, an octopus will typically flee. When attacked, it draws water into its mantle cavity and expels it with great force through a funnel. The result is a jet-propelled exit, usually behind a cloud of “ink,” a dark substance the octopus ejects for defense. The ink cloud paralyzes the attacker’s sense of smell. An octopus can also camouflage itself by rapidly changing the color and texture of its skin.

The octopus is an intelligent animal. Experiments have shown that it has the ability to learn and both a short- and long-term memory. When presented with two different shapes, for example, the octopus will choose the one leading to a food reward after 20 to 30 trials. Some marine experts reportedly design puzzles and mazes to stimulate captive octopuses.

IV

Reproduction and Life Span of the Octopus

A male interested in mating approaches a female just close enough to stretch out a modified arm, the hectocotylus, and caress the female. This arm has a deep groove between the two rows of suction cups and ends in a spoonlike tip. After a period of love play the male inserts its arm under the mantle of the female, and the spermatophores travel down the groove on the hectocotylus to the female’s oviduct. Soon after mating, the female begins to lay eggs, each enclosed in a transparent capsule, in its lair. The common octopus can produce up to 500,000 eggs in one batch.

The time it takes for the eggs to hatch varies according to water temperature and other environmental conditions, but may last as long as four to five months. During this time the female guards the eggs, jetting water to aerate and clean them. Female octopuses do not eat while protecting their eggs, and often die soon after they hatch. The larvae (developing young) of some species, such as the white-spotted octopus, float to the surface and become part of the plankton for about a month, then sink and begin their normal life on the sea bottom. These species are found throughout the world because the larvae move with the currents and tides. Many of the smaller octopus species die after reproducing, which occurs at an estimated five months to three years of age. Larger species may live longer.

Scientific classification: Octopuses belong to the order Octopoda. The common octopus is classified as Octopus vulgaris, the Atlantic pygmy octopus as Octopus joubini, and the white-spotted octopus as Octopus macropus, all of the family Octopodidae.

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