phylum echinodermata n.
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Phylum Echinodermata. Ch.16. Phylum Echinodermata. ~7,ooo Species Triploblastic, coelomate, ALL marine Pentaradial symmetry (Body parts arranged in fives or a multiple of five) Complete Digestive Tract Regeneration Most are dioecious, some are moneocious Most use external fertilization

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phylum echinodermata1
Phylum Echinodermata
  • ~7,ooo Species
  • Triploblastic, coelomate, ALL marine
  • Pentaradial symmetry
    • (Body parts arranged in fives or a multiple of five)
  • Complete Digestive Tract
  • Regeneration
  • Most are dioecious, some are moneocious
  • Most use external fertilization
  • Water-vascular system (Figure 16.4)
    • Madreporite  Stone canal  Ring canal  5 radial canals branch off  Lateral canals  Tube feet
class asteroidea
Class Asteroidea
  • Sea stars, about 1,500 species
  • May be brightly colored with red, orange, or blue
  • Most have 5 arms that radiate from central disc
  • Oral surface down and in middle
  • Dermal branchiae in skin (gas exchange)
  • Water-vascular system
  • Suction disks of tube feet are used for attachment and movement
  • Sea stars feed on snails, bivalves, crustaceans, corals, and a variety of other food items
  • Are well known for regeneration, they can regenerate any part of a broken arm….an entire sea star can be regenerated from a broken arm IF the arm contains a portion of the central disk…it is a slow process, taking up to a year for complete regeneration.
class ophiuroidea
Class Ophiuroidea
  • Greek for snake (orphis) tail (oura) in the form of (oeides)
  • Brittle stars & Basket stars, over 2,000 species
  • Most diverse group of Echinoderms
  • Are predators and scavengers
  • The mouth leads to a sac-like stomach, and no part of the digestive tract extends into the arms
  • Water-vascular system used for capturing prey, not for locomotion
  • Tube feet lack suction cups, successive ossicles articulate and are acted upon by large muscles to produce snake like movement (hence the name of the class)
  • Like sea stars, ophiuroids can regenerate lost arms. If a brittle star is grasped by an arm, the brittle star will cast off the arm, this process called autonomy (Greek: autos=self + tomos=to cut) is used in escape reactions!
  • Dioecious, and males are generally smaller than females.
class echinoidea
Class Echinoidea
  • Sea urchins, sand dollars, about 1,000 species
  • Sea urchins live on hard substrates, sand dollars live in sand or mud
  • Feed on dead animal remains, plankton, algae
  • Aristotle’s lantern – 35 teeth-like ossicles (a chewing apparatus) used in feeding
  • Urchins – hard surfaces, move by spines and tube feet, some have venom
  • Sand Dollars – burrow just below surface
class holothuroidea
Class Holothuroidea
  • Sea cucumbers, about 1,500 species
  • Found at all depths of the ocean, and crawl or burrow
  • Have no arms, and they are elongated along the oral-aboral axis and have enlarged tube feet around mouth.
  • Are ~10-30 cm in length
  • Ingest organic matter, use tentacles
  • Edible – “trepang” in Asia (body wall boiled and dried)
  • Water-vascular system internal & has coelomic fluid
  • Mostly sea cucumbers are defenseless against prey…but….
    • Many produce toxins that discourage predators
    • Some eject sticky internal tubules that contain toxins (from the anus) to confuse predators
    • Some cause internal structures to explode (basically blowing up their body) in response to chemical and physical stress as a defensive adaptation to discourage predators, regeneration of lost parts follows!
class crinoidea
Class Crinoidea
  • Feather stars, sea lilies, about 230 species
  • Most primitive of all echinoderms
  • Many species in fossil record
  • Attach permanently to a substrate and filter water for plankton
  • Sea lilies attached by a stalk
  • Feather stars have no stalk
  • Feather stars swim by raising and lowering arms