In a galaxy, far, far away, weird, alien life forms duke it out for intergalactic supremacy. Meanwhile, in another alien environ ment right here on Earth, the oceans provide the stage for an intense, real life and death struggle that eclipses any intergalactic confrontation on the silver screen.

The bizarre adaptations and behaviours of science fiction aliens are no match for the real life drama that can be found in a few meters of ocean bottom. You'll never see Jaba the Hutt protrude his stomach out through his mouth in order to enjoy a meal, or Darth Vader oozing toxic poisons or suffocating slime to rid himself of an opponent.

Some of the most common animals we encounter while diving are members of the phylum Echinodermata, a diverse and ancient group of animals that includes the sea stars, urchins and sea cucumbers. Found throughout the oceans of the world, these animals have survived for over 500 million years by relying on an impressive arsenal of offensive and defensive mechanisms that include thousands of suction-cupped tube feet, noxious slime, paralyzing chemical secretions, poisonous spines, erosive digestive juices and even an ability to regenerate lost body parts. With bodies composed of hard calcareous plates, some times covered in spines, or tough, slippery hide, most of the Echinoderms would seem to make unappetizing prey with little need for protection. But the struggle for survival in the oceans is great and some Echinoderms form a very important link in the food chain, being consumed by bottom fish, crabs, sea birds, marine mammals, members of their own family and man.

The most active and determined predators in this group are the sea stars who will just as quickly feed on members of their own family, and other Echinoderms, as anything else. Powered by a water vascular system, thousands of tube feet lining the undersides of their arms, allows most sea stars to move at surprising speeds, the giant Sunflower star has been clocked at over 100 centimeters a minute! But the tube feet are also employed in feeding, and once in the grip of a sea star, resistance is futile. Even buried prey poses little problem, as a sea star will dig down up to a foot to unearth it's meal. And if it can't bring the meal to it's stomach, it will simply take it's stomach to the meal. When dining on clams or mussels, a sea star slowly pulls the two halves of the shell apart using their powerful tube feet and, with a gap of a millimetre or less disgorges it's gelatinous stomach, inserts it between the shell and secretes digestive enzymes, reducing it's prey to a more absorbable form.

But the sea stars' prey are not without their defenses. The swimming anemone will quickly detach itself from the rock and swim away at the approach of the garlic-smelling leather star. Cockles use their large muscular foot to run or vault away and the swimming scallop will open and close its shell rapidly, looking like a set of jet propelled false teeth as it makes a retreat through the water. Abalone will writhe violently, making it as difficult as possible for the sea star's tube feet to get a good grip, and nudibranchs release poisonous spears or toxic chemicals and acids as a defense.

Defense mechanisms for the Echinoderms are as varied as the animals themselves. Most are capable of some form of locomo tion, and retreat is often the first defense. The aboral, or top surface, of most sea stars is covered with an array of spines and small, pincer-tipped appendages called pedicellaria which are mainly to keep the surface clean but also used to detract predators and even capture prey. The fish eating star Stylasterias forreri has such large pedicellaria that it is able to catch small fish. And a few sea stars, such as the Pacific species Pteraster tesselatus , secrete copious amounts of noxious and suffocating slime as a deterrent.

Sea urchins rely on their shell plating, along with a covering of spines and poisonous pedicellaria, a good combination against all but the most determined predator. They will usually run when confronted but when forced to defend itself the urchin will often flatten it's spines in order to expose the thousands of pedicellaria and allow them to go to work.

The softer bodied sea cucumbers would seem to be more vulnerable to predators but are also capable of defending themselves when the need arises. Some have very tough and slippery skins or armor plating and most are capable of surprisingly quick motion when threatened. Others adopt a more passive defense, hiding, burrowed among rocks, leaving only vital organs exposed for respiration and feeding. These can be retracted quickly when threatened. When attacked, some cucumbers, mainly those in tropical regions, resort to the unappetizing habit of regurgitating their sticky, foul tasting, and replaceable, intestines. A few tropical cucumbers are also capable of secreting neurotoxins from their skin in order to dissuade predators.

The oceans are an alien world to some but for the interested and patient observer it is home to a bizarre cast of characters waiting to delight and amaze us as they continue their unending struggle to survive.