13'4 Ehinoderms

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13.4 Ehinoderms
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Echinoderm Characteristics

• Echinoderm means spiny skinned.
• Have a hard endoskeleton covered by a thin bumpy
  or spiny skin.
• Have radial symmety.
• All have a mouth stomach and intestines.
• Have no brain or head, do have nerve ring around
  mouth.
• They have cells in the skin that detect light and
  touch

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Water vascular system

• The water-vascular system is a network of water
  filled canals connected to thousands of tube
  feet.
• Tube feet are hollow thin walled tubes with a
  suction cup at the end.
• Use tube feet to move and get food.

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Types of echinoderms

• There are over 6000 species.

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Sea Stars

• Have at least five arms around the central point.
• Use their tube feet to open shells.
• Can push their stomach inside the shells of the
  prey to digest it.
• Reproduce sexually when they release sperm and
  egg into the water.
• Can replace lost arms using regeneration.

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Brittle stars

• Have arms that are slender and fragile, and break
  off easily.
• Arms that break off easily let the star escape.
• Arms are replaced quickly.
• Use arms to move not tube feet.
• Tube feet are used to move food to the mouth.

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Sea Urchins Sand Dollars

• Disk or globe shaped with spiny skin.
• Many have long spines and some have poisonous
  venom.
• Sea urchins have tooth like structures around the
  mouth.

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Sea Cucumbers

• Soft bodied echinoderms no skeleton.
• Rows of tube feet on top and bottom of the body.
• Tentacles surround the mouth
• When threatened can expel its internal organs
  which regenerate in a few weeks.

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Origins

• Many fossils exsist.
• Date back more than 400,000 years
• Thought to be more closely related to vertebrates
  than other invertebrates.
• Embryo develops in a similar way to those of
  vertebrates.