Echinoderms
Echinoderms
Echinoderms (pronounced: /ˈɛkɪnoʊˌdɜːrm/), from the Greek words "echinos" meaning "hedgehog" and "derma" meaning "skin", are a phylum of marine animals found at every ocean depth. The phylum contains about 7000 living species, making it the second-largest grouping of deuterostomes, after the chordates (which include the vertebrates, such as birds, fishes, mammals, and reptiles).
Echinoderms are characterized by radial symmetry, a water vascular system, an endoskeleton, and a simple nervous system. They exhibit five-fold symmetry, or pentamerism, which is not seen in other animal phyla.
Classification
Echinoderms are classified into five classes:
- Asteroidea (starfish or sea stars)
- Ophiuroidea (brittle stars)
- Echinoidea (sea urchins and sand dollars)
- Crinoidea (sea lilies and feather stars)
- Holothuroidea (sea cucumbers)
Anatomy
Echinoderms have a unique water vascular system. This system is a network of fluid-filled canals derived from their coelom (body cavity) that function in gas exchange, feeding, sensory reception, and locomotion.
Reproduction
Most echinoderms have separate sexes and reproduce sexually. Fertilization is usually external, but some species have internal fertilization and brooding. Many echinoderms also have the ability to regenerate lost body parts.
Ecology
Echinoderms play important roles in marine, benthic ecosystems. Sea urchins, for example, can control the distribution of algae. On the other hand, starfish are well-known predators in many ecosystems.
See Also
References
External Links
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