Echinoderms: Spiny-skinned animals

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Echinoderms Spiny-skinned animals

• Section 31.1

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Animal Development

• Echinoderms are related to vertebrates due to
  their early development
• The gastrula is the early embryo a hollow ball
  of cells with an opening called a blastopore
• Other animals are protostomes their mouth
  develops first from or near the blastopore
• Echinoderms and chordates (vertebrates) are
  deuterostomes their anus develops from the
  blastopore their mouth develops second from
  another part of the gastrula

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Development, continued

• First deuterostomes were marine echinoderms
• Also the first animals to develop endoskeletons
• Chordates (including all vertebrates) are
  deuterostomes

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Features of Modern Echinoderms

• Endoskeleton
• Calcium-rich
• Composed of plates called ossicles
• In adults the plates may fuse and hold spines
  that protrude through the skin
• Five-part radial symmetry
• Bilateral symmetry as larvae develop radial
  symmetry as adults
• Have no head or brain, only a central ring of
  nerves with branches into each arm

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Features, continued

• 3. Water-vascular system
• Made of interconnected canals and hollow tube
  feet
• The tube feet extend through the ossicles
• They are used for locomotion and feeding, as well
  as some gas exchange and waste excretion
• 4. Coelomic circulation respiration
• The body cavity acts as a simple circulatory and
  respiratory system
• Skin gills may grow along the spines to increase
  surface area

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Echinoderm Diversity

• Sea Stars
• Mostly carnivores
• Brittle Stars
• The largest class of echinoderms
• Have slender, branched arms
• Most are filter feeders
• Sea Lilies and Feather Stars
• Most primitive echinoderms
• Their mouth is located on their upper surface
• Usually sessile

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Sea Stars
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Brittle Stars
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Sea Lilies
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Feather Star
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Diversity, continued

• Sea Urchins and Sand Dollars
• Lack distinct arms
• Flattened bodies with protruding spines that may
  have poison
• Sea Cucumbers
• Soft and slug-like
• Ossicles are not fused
• Sea Daisies
• Small group, discovered in deep water

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Sea Urchin
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Sand Dollar
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Sea Cucumber
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Sea Daisy