Echinoderms

1
Echinoderms

• Section 38.1

2
Echinoderms

• Examples sea stars, sand dollars, sea urchins,
  sea cucumbers
• Marine environments
• Brilliantly colored
• Radial symmetry

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4 Unique Characteristics

1. Ossicles calcium carbonate plates that make up
   exoskeleton
2. Water-vascular system network of water-filled
   canals inside body

4

• 3. Tube feet small, movable extension of w-v
  system which aid in movement, feeding,
  respiration, excretion
• 4. Pentaradial symmetry body parts extend from
  center along 5 spokes

5
Classification

• 6 classes of echinoderms (only 5 discussed in
  textbook)
• Class Crinoidea
• Class Ophiuroidea
• Class Echinoidea
• Class Holothuroidea
• Class Asteroidea

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Class Crinoidea

• Examples sea lilies, feather stars
• Crinoid means lily-like
• 5 main arms that branch to form up to 200 more
  arms
• Filter feeders
• Mouth faces up

7
Class Ophiuroidea

• Largest class with examples such as basket stars
  brittle stars
• Ophiuroidea means snake-tail
• Live on bottom of ocean
• Regeneration of broken arms
• Long, narrow arms allow for quick movement

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Class Echinoidea

• Examples sea urchins sand dollars
• Echinoidea means spinelike
• Compact, rigid endoskeleton that surrounds
  internal organs
• Spines can have barbs or venom

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Class Holothuroidea

• Example sea cucumber
• Holothuroidea means water polyp
• Armless
• Ossicles are not connected thus soft bodies
• Tentacles around mouth to capture prey

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Class Asteroidea

• Example sea star (starfish)
• Asteroidea means starlike
• Variety of sizes, shapes, and colors
• Compete with humans for oysters, clams, etc

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Sea Stars

• Section 38.1 continued

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External Structure

• Several arms extending from central region
• Two rows of tube feet on underneath side of each
  arm
• Oral surface side where mouth is located
• Starfish underside
• Aboral surface side opposite of mouth

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• Rough texture due to short spines
• Pedicellariae tiny pinchers surrounding of each
  spine that keep body free of foreign objects

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Water-Vascular System

• Network of water-filled canals that are connected
  to the tube feet
• Water movement
• Madreporite (sievelike plate on aboral surface) ?
  stone canal ? ring canal (encircles mouth) ?
  radial canal (extends to each arm) ? tube feet
• Ampulla bulblike sac at end of tube feet that
  allows for movement and suction

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Feeding Digestion

• Prey mollusks, worms, clams
• Cardiac stomach can be turned inside out through
  mouth during feeding
• Digestive pathway
• Mouth ? cardiac stomach ? pyloric stomach ?
  digestive glands in each arm ? anus

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Other Body Structures

• No circulatory, excretory, or respiratory
  systems!
• Skin gills thin walls of tube feet that allow
  gas exchange
• Nervous system nerve ring (around mouth),
  radial nerves (length of each arm), eyespots (end
  of each arm), tentacles

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Reproduction Development

• Separate sexes each arm has sex organs
• External fertilization
• After 2 months of swimming they settle to bottom
  of ocean and metamorphous into adult
• Regeneration (asexual)
• As long as part of the central region stays in
  tact