Live in the dark depths of the sea where the temperature of the water is always close to freezing, even at the equator, and the pressure may be as much as 15,000 pounds per square inch compared to 15 pounds per square inch at sea level. More than 80 per cent of the ocean floor is a mile or more below the surface, the depth at which the abyssal zone begins in most areas. In these deep waters sponges and sea lilies are common on the bottom. There are numerous single-celled animals (Protozoa) each with a little “Skeleton” of its own, and a variety of other inverte-brates, including sea anemones, corals, segmented worms, clams, snails, starfish, sea-cucumbers, sea urchins, horseshoe crabs, barnacles, and crustaceans. Although no group is especially abundant, animals of all major groups live in the deep sea. They apparently evolved from forms that at one time lived close to the surface. No plants can live in these sunless waters so abyssal animals feed on each other or on dead plants and animals that sift down steadily from the lighted area of the sea above. Many abyssal animals have special organs for producing red, violet, or green lights. Some have enormous eyes to see in the dimness; others have small but very sensitive eyes, while still others have no eyes at all. Those with weak or no eyes often have sensitive “feelers.” Some deep-sea fishes have tremendous mouths and numerous long, sharp teeth. Many can stretch their stomachs to hold animals larger than themselves. Sponges and sea lilies grow on long stalks. Sea urchins and sea cucumbers have greatly flattened bodies, while crawling types of crustaceans have extra long legs covered with bristles to keep them from sinking into the soft mud. Lime forms poorly in the depths so the shells of animals are weak or lacking. Due to the great pressure, the body cavities of abyssal animals are filled with oil or water rather than air. Most abyssal animals are a dull red, violet, brown, or black, and they are generally smaller than their surface relatives . Fishes that live in the abyssal zone are small, few attaining a length of three feet. The invertebrates of the deep are among the largest in their groups, however. Glass sponges are as much as four feet in diameter and three feet tall.