The earth's axis of rotation wobbles like a spinning top. There are two periods (a wobble within a wobble): 19,000 AND 23,000 years. Precession has a profound effect on the earth's climate.
The family Asterinidae and Ophidiasteridae also contain several species that are common to the Bahamas and the Keys. Asterina folium is a tiny species which rarely exceeds one inch in overall diameter. Ranging in color from white and yellow to blue, Asterina folium is found most frequently in coral reefs, hidden beneath the corals. Another species that shares Asternia folium’s preference for a coral reef habitat is Copidaster lymani, of the Ophidiasteridae family. This species may grow as large as 12 inches in diameter, but the average size is around 9 inches. The arms of this starfish are often not the same length, and the color of the animal is dark red. Linckia guildingii and Ophidiaster guildingii, also of the family Ophidiasteridae, are two other species found in coral habitats. The former might be seen in the Keys and the Bahamas, while the later is common only in the Florida Keys. (Hendler, Kier, Miller, and Pawson, 74-78)
From the family Asteropseidae, Poraniella echinulata holds the title of one of the smallest sea stars in the tropical western Atlantic. Species are rarely bigger than 1 inch in diameter, but may stand out due to their bright red-orange color. Poraniella echinulata are never found in large numbers, possibly due to the fact that these starfish prefer deep reefs beyond scuba depths. In the Bahamas, species have been collected from vertical rock walls in waters as deep as 492 feet by using research submersibles. (Hendler, Kier, Miller, and Pawson, 81-82)
A species that we may have more of a chance to see is Oreaster reticulatus, of the family Oreasteridae. Labeled by Hendler, Miller, Pawson, and Kier as the “most widely known and most easily identified member of the Caribbean marine biota” (82), this species may grow as large as 20 inches in diameter. Varying in color, the Oreaster reticulatus is seen from boats roaming reef flats, lagoons, and mangrove channels. Because of its accessibility, this species is often the victim of human exploitation, and is now rare in some areas where it once was common. (Hendler, Kier, Miller, and Pawson, 82-83)
Echinaster sentus, of the family Echinasteridae family, is moderate in size with an overall diameter around 7 inches. Its color is widely varied: deep red, reddish brown, dark purple, pale violet, yellow brown, and purple all have been reported. The species has been studied off Big Pine Key in the Florida Keys, where it has thrived on gravel and clay sediment near mangroves. Echinaster sentus also has been reported in the Bahamas Islands. (Hendler, Kier, Miller, and Pawson, 85-86)
Although starfish may look quite simple, they are in fact fairly complicated beings. One of the most unique features of starfish and other echinoderms is their water vascular system. (Banister and Campbell, 275) In the center of a sea star’s body is a disk called a sieve plate, or madreporite, through which water is drawn in and sent to the arms of the animal. (Fichter, 3) The pressure created is then used by tube feet, which are tiny structures underneath the starfish’s arms. As the water is pumped, each tube foot becomes like a suction cup, enabling starfish to anchor themselves to a variety of structures, such as coral reefs and rocks. Tube feet are essential to a sea star’s survival, as they aid in locomotion as well as feeding. (Fichter, page 3)
Other physical features of sea stars include papulae, pedicellariae, ocular plates, and the anus. Papulae contribute to the “furry” feeling that some starfish possess. (Hendler, Kier, Miller and Pawson, 62) They are transparent and retractable and serve to aid respiratory gas exchange. Pedicellariae are the pincer-like spines that act to rid the area around the papulae of debris. Pedicellariae are very to when identifying starfish, because the amount and shape are very different among the species. At the end of each arm, an ocular plate is used to sense light and darkness. (Fichter, 3) This enables the animal to move away from bright light. Finally, an anus is present in some species of starfish. If no anus exists, the animal ejects waste through the mouth. (Blaxland, 8)
Sea stars are very diverse in their feeding strategies. Carnivorous species feed on shellfish, sponges, crabs, corals, worms, and other echinoderms. Some are scavengers and prey on dead fish and other creatures. Deposit feeders also occur -- such starfish fill their stomachs with mud and then extract organic matter and microscopic organisms on which they feed. (Bender, 79)
A starfish may feed either intraorally or extraorally. Intraoral feeders take live prey, the digestion of which may take up to a week, into their stomachs. Extraoral feeders extend their stomach from their disk and apply it directly to their food. Some species of starfish attach themselves to a mollusk and proceed to persistently pull apart the shell of the animal with their tube feet. (Hendler, Kier, Miller, and Pawson, 63-64) Some mollusks manage to keep their shell closed for days, but eventually the starfish win out and devour the prey with their stomach. (Fichter, 4)
Starfish may reproduce either sexually or asexually. When asexual reproduction takes place, the animal breaks itself into two pieces. From these pieces, the animal is able to regenerate new body parts, eventually becoming whole again. Regeneration is also used when a starfish loses an arm, which is a fairly common occurrence. Although helpful, the process of regeneration may take up to a year. (Blaxland, 12-13)
Sexual reproduction is slightly more complicated. Some species of starfish spawn, during which a male releases sperm and a female releases eggs, usually within close proximity to one another. When the egg and sperm join inside the water, a microscopic larva begins to grow. Within several months the starfish begins to resemble the shape and characteristics of an adult. Average echinoderms do not usually reach their full adult size until several years after their birth. (Blaxland, 10-11) A few species of starfish are brood-caring, meaning the larvae are hatched from eggs. Most of these starfish live in the polar oceans. (Grzimek, 378-379)
Starfish are important to the well-being of the marine communities they inhabit. The management of their populations is crucial to the health of ocean systems, especially reef environments. Perhaps the most well-known species, Acanthaster planci, or the crown-of-thorns starfish, have recently decimated large populations of corals with their voracious feeding. (Bender, 79) The species Asterias, found on the North Atlantic coast, also has done great damage to the shellfish population with which they share the water. On the other hand, many species of starfish have been severely compromised by human harvesting, for such purposes as biological supply and tourist trinkets. (Hendler, Kier, Miller and Pawson, 66) It is thus extremely important that the creatures are understood, so that we may monitor and preserve the species to the best of our ability. Beautiful animals, starfish deserve not only protection, but appreciation.
Banister, Keith and Campbell, Andrew. The Encyclopedia of Aquatic Life. Andromeda
Oxford Limited. 1985.
Bender, Lionel. Simple Animals: Encyclopedia of the Animal World. Equinox Ltd.
Behrens, David W. and Gosliner, Terrence M. and Williams, Gary C. Coral Reef
Animals of the Indo-Pacific. Sommerset Rise. Monterey, CA. 1996.
Blaxland, Beth. Sea Stars, Sea Urchins, and Their Relatives. Chelsea House Publishers.
Fichter, George S. Starfish, Seashells, and Crabs. Western Publishing Company, Inc.
Racine, WI. 1993.
Grzimek, Bernhard. Grzimek’s Animal Life Encyclopedia: Mollusks and Echinoderms.
Van Nostrand Reinhold Company. New York, New York. 1974.
Hendler, Gordan and Kier, Porter M. and Miller, John E. and Pawson, David L. Sea
Stars, Sea Urchins, and Allies. Smithsonian Institution. 1995.
Hurd, Edith Thacher. Starfish. Englewood Cliffs, NJ. Harper Collins. 2000.
Krantz, Lucretia and Zim, Herbert S. Sea Stars and Their Kin. New York, New York.
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