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Echinoderms (Echinodermata)


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There are main 5 classes of living echinoderms:
crinoids (sea lilies and feather stars); asteroids (STARFISH); ophiuroids (brittle stars); echinoids (SEA URCHINS, etc); and holothuroids (sea cucumbers).
Echinoderms have been well preserved as FOSSILS; all existing classes and several others now extinct were present in the Ordovician (505-438 million years ago). They may have originated in the Precambrian (over 570 million years ago).
Common name : sea lilies, Sea Stars(STARFISH), sea urchins, sea cucumbers, and brittle stars.
Echinoderms occupy all habitats including coral reefs, mangroves, seagrass and soft-bottom areas.
Except for a few species which inhabit brackish waters, all echinoderms are benthic organisms found in marine environments. Echinoderms inhabit depths ranging from shallow waters at tide lines to the deep sea.(Barnes, 1987; Brusca and Brusca, 2003; University of Alabama Center for Communication and Educational Technology, 2000; Waggoner, 1999)
Habitat Regions
• temperate
• tropical
• polar
• saltwater or marine
Aquatic Biomes
• brackish water
Other Habitat Features
• intertidal or littoral
GeoGraphy and eco-system
Geographic Range
Mainly a marine group, echinoderms are found in all the oceans. (Brusca and Brusca, 2003)
• arctic ocean
• indian ocean
• atlantic ocean
• pacific ocean
• mediterranean sea
Sea urchins are among the main herbivores on reefs and there is usually a fine balance between the urchins and the kelp and other algae on which they graze. A diminution of the numbers of predators (otters, lobsters and fish) can result in an increase in urchin numbers causing overgrazing of kelp forests with the result that an alga-denuded "urchin barren" forms.
Work cited:
Lawrence, J. M. (1975). "On the relationships between marine plants and sea urchins". Oceanographic Marine Biological Annual Review 13: 213–286.
Ecosystem Roles
Echinoderms are usually intricate parts of their ecosystems. Many asteroids are keystone species. Sea urchins, if not controlled by predators, may overgraze their habitat. Asteroids have several commensals, including polychaetes that feed on leftovers from the sea star's prey items. (Barnes, 1987; Brusca and Brusca, 2003)

Ecosystem Impact: keystone species

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Echinoderms (Echinodermata)

  1. 1. echinos = spiny derma = skin ata = to bear Phylum Echinodermata:
  2. 2. General Characteristics: 1. Calcareous endoskeleton, often bearing visable spines. 2. Adults with pentaradial symmetry, frequently with central disc and 5 (or more) radiating arms or rays. 3. Water-vascular system used in locomotion, attachment, &/or feeding.
  3. 3. Special Note: • The larval forms are bilaterally symmetrical. This symmetry is lost during transition to adulthood. • Why transition from bilateral symmetry in larvae to radial symmetry in adults? Unlike a bilateral symmetrical adult, an echinoderm can greet its environment from all sides and respond to it.
  4. 4. Pentaradial symmetry: - a form of radial symmetry: parts arranged in fives, or multiples of fives, around an oral-aboral axis (top and bottom of a dinner plate) - Since the larval stages are bilaterally symmetrical, they are believed to evolved from bilateral ancestors.
  5. 5. Why 5 arms instead of 6? • The 5 part organization may be advantageous because joints between skeletal ossicles (joints) are never directly opposite one another, as they would be with an even number of parts. • Having joints on opposite sides of the body in line with each other could make the skeleton weaker.
  6. 6. Additions to our directional terminology: • Aboral: upper surface (think of the part of the dinner plate you eat from) • Oral: lower surface (think of the part of the dinner plate on the table)
  7. 7. Habitat: • - marine environments - bottom of deep seas -bottom of coastal shores Niche: • - relatively slow moving • - feeding – *some species feed on animal remains on the ocean floor – *some filter plankton through their mouth pore – *some scrape food off rocks – *others are predaceous on mollusks, arthropods
  8. 8. Classes of Echinodermata: Class Stelleroidea examples: sea stars (starfish), brittle stars sea stars: • - general characteristics: • 1. most common echinoderm; central disc and 5 arms (or rays) radiating from disc • 2. may be various colors of red, purple, green, blue and yellow • 3. range in size from about 2 cm to nearly a meter • - found on pier pilings and rocks in tide pools along coasts
  9. 9. Classes of Echinodermata: Class Stelleroidea examples: sea stars (starfish), brittle stars brittle stars: • - general characteristics: • 1. a distinct disc set apart from the arms • 2. slender, articulating arms • 3. rapid, serpentine (snakelike) movements • - found on the seashore, burrowed in sand or • deep sea sediments or under rocks and kelp
  10. 10. Class Echinoidea examples: sand dollars, sea urchins sand dollars • - general characteristics • 1. range in size from 1-15 cm • 2. flattened skeleton (test) covered with a dense thicket of tiny spines • 3. aboral surface exhibits flower petal-shaped grooves (petaloids) that correspond to the arms of sea stars and brittle stars • 4. tube feet in the petaloids are used in locomotion
  11. 11. Class Echinoidea examples: sand dollars, sea urchins sea urchins • - general characteristics • 1. rounded body shape • 2. long spines on exterior • 3. the areas corresponding to the rays of the sea stars are fused
  12. 12. Class Holothruoidea examples: sea cucumbers, feather stars sea cucumbers • - general characteristics • 1. long, cucumberlike body lacking a solid, calcareous skeleton • 2. oral end has a ring of retractile tentacles that represent highly modified tube feet • - found on the sea bottom, often partially • submerged in mud or sand, or among intertidal • rocks
  13. 13. Class Holothruoidea examples: sea cucumbers, feather stars feather stars • - general characteristics • 1. most primitive of the living echinoderms • 2. from a small cup or calyx, protrudes five flexable arms (rays) with branches (pinnules) very much like pine needles
  14. 14. Digestive System: • -have an anus, but it is almost nonfunctional; undigested food is expelled back through the mouth • -respond to light, chemicals, and various mechanical stimuli
  15. 15. Reproduction: • dioecious – the two sexes are indistinguishable externally • gamete release by one individual is accomplished by the release of spawning pheromones, which induce other sea stars in the area to spawn, increasing the likelihood of fertilization
  16. 16. Nervous System: • o nerve ring that encircles the mouth • o radial nerves that extend into each arm (these coordinate the functions of the tube feet) • other nervous elements are in the form of a nerve net associated with the body wall