The Mighty Throng A tenacious starfish pulling open a scallop. When the hungry starfish comes upon its prey, it surrounds the creature with its five arms and pulls with its suction pads until the shell parts.
PHOTO: Leannart Nilsson, Marvels & Mysteries of Our Animal World. © The Reader's Digest Association, Inc. 1964.
genus: Asterias species: rubens
Asterias (any echinoderms belonging to the class, Asteroidea) typically have five arms radiating from a small central body with a toothless mouth on its underside. The number of arms may, however, be from four up to 50. Some Common Starfishes, which normally have five arms, may have from three to seven. Purple and orange-pink are the most common colours of Starfishes found around the Stanley Park waterfront. The North Pacific is home to more species of Starfishes than anywhere else.
The Starfish moves about by means of numerous tube-feet arranged in two or four rows along a groove on the underside of each arm. The tube-feet are hollow, muscular cylinders connecting at their bases with a system of tubes a vascular system filled with water. The feet are controlled and propelled hydraulically. At the tips of these feet there are usually suction discs which also have sticky secretions. Starfishes have the power of regeneration. A complete Starfish can grow out from a torn or damaged limb.
Starfish are generally carnivorous, feeding on molluscs, worms, crustacea, fish and other echinoderms. Asterias prey on bivalves such as oysters opening them by arching over them and pulling on the shell valves with their tube-feet, until the bivalve secumbs with fatigue. Starfishes raid oyster and mussel beds and feed on the shellfish. Once a shellfish is forced open, the Starfish exerts its stomach into the opened shellfish and excretes digestive juices. Feeding is very slow, almost as slow as the feeding of a pitcher plant upon a fly. Starfish have also been blamed for the dramatic largescale destruction of coral reefs.
Both male and female Starfish have two reproductive organs in each arm, each one opening by a pore at the base of the arm. There is usually one breeding season a year, where millions of eggs may be released into the sea. Asterias may release two to three million within a couple of hours.
Starfish, with their calcareous-plated bodies, look as inanimate as pebbly stones. Breathing, drinking and moving are a combined operation. Starfish can move in any direction. They creep along the sea floor by aternately fastening the tube feet then withdrawing them. Their feet have tiny suction tubes which the Starfish operates by rythmically filling with water then drawing the water back out.
Starfish don't see where they are going.They have a tiny crimson eyespot at the tip of each of its arms, but these inform them of no more than light and dark.
Funk & Wagnalls Wildlife Encyclopedia 18. Funk & Wagnalls, Inc. New York, NY, 1969/1970.
Marvels & Mysteries of Our Animal World: A Family Guide to the Fascinating Creatures of Earth, Sea and Sky. Coronet Books, The Reader's Digest Association, Pleasantville, New York. Copyright © The Reader's Digest Association, Inc. 1964.