What Is the Meaning of Echinoderm?
According to the Ocean Research Group, the term "echinoderm" refers to any animal within the phylum, or group of animals with similar characteristics, Echinodermata. Echinoderms are only found in salt water. The Ocean Research Group states that the most unifying characteristic among echinoderms is that they all have radial symmetry, which means the animals' appendages are arranged around a central focal point. Some well known echinoderms include sea stars, sea urchins and sea cucumbers.
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Movement
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Echinoderms move by means of a water vascular system. The underside of a sea star, for example, is covered in hundreds of tiny feet. The number of feet varies from species to species. These podia, or tube feet, are filled with sea water. Using this sea water to expand and contract their tube feet, sea stars and other echinoderms can pull themselves across the ocean floor in a walking fashion.
Diet
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Different species within the phylum Echinodermata feed differently. Research from the University of Michigan Museum of Zoology suggests they obtain food in one of several ways. Some echinoderms are suspension feeders who catch passing particles with their outstretched arms. Others are predators and scavengers who hunt prey and use their water vascular system to consume prey through mouth-like sucker appendages. Still other echinoderms, such as sea urchins, have hard plate-like teeth which allow them to graze on algae.
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Sea Stars
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The scientific community, according to the Oceanic Research Group, has been moving away from the term "star fish" and has begun using the term "sea star," since sea stars have very little in common with fish. One characteristic of sea stars is their ability to regenerate lost limbs over time. Although lost limbs in some species can regrow into another sea star, most severed limbs simply die.
Sea Urchins
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Sea urchins belong to the class Echinoidea, a more specific classification of animals within the phylum Echinodermata. The most obvious characteristic of sea urchins is their spine-covered body. This is a defense mechanism against predators, and muscles attached to their spines allow them to point their spines in the direction of a predator.
Sea Cucumbers
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The water vascular system of sea cucumbers differs slightly from that of other echinoderms. Instead of sea water, the tube feet of sea cucumbers are filled with a special body fluid. Sea cucumbers have a unique defense mechanism, called self-evisceration, in which they will expel some of their internal organs to scare away predators. The animal will then regrow new organs.
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References
Resources
- Photo Credit starfish image by Emerkaza from Fotolia.com
