Phylum echinodermata

Phylum echinodermata

• 1.
  echinos = spinyderma = skin ata = to bear Phylum Echinodermata:
• 2.
  General Characteristics: 1. Calcareousendoskeleton, often bearing visible 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.
  Special Note: • Thelarval 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.
  Pentaradial symmetry: - aform 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.
  Why 5 armsinstead 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.
  Additions to ourdirectional 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.
  Habitat: • - marineenvironments - 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.
  Classes of Echinodermata: ClassStelleroidea 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.
  Classes of Echinodermata: ClassStelleroidea 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.
  Class Echinoidea examples: sanddollars, 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.
  Class Echinoidea examples: sanddollars, 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.
  Class Holothruoidea examples: seacucumbers, feather stars sea cucumbers • - general characteristics • 1. long, cucumber like 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.
  Class Holothruoidea examples: seacucumbers, 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