Biology 11- Echinoderms

feeding

• Nerve ring that surrounds the mouth and radial nerve that connect the ring with body sections 

• Sensory cells detect food 

• Starfish have 200 sensitive cells (EYESPOTS) at arm tips 

• Statocysts  

respiration

• Tissue on tube feet 

• Some have skin gills Starfish 

  • Carnivores 

  • Pry open shells with tube feed 

  • Flip stomach out  

Sea Urchins 

• Herbivores 

• Scrape algae using 5 part jaw 

Brittle stars 

• Use tube feel on flexible arms to catch floating food 

Sea Cucumbers 

• Detritus feeders 

• Moves like a bulldozer and eats everything on the floor 

internal transport system

• Closed circulatory system 

• System for gas exchange is NOT needed because done by tube feet 

• Nutrient distribution done by digestive glands and fluids in body cavity Tissue on tube feet 

• Some have skin gills 

excretion

• Solid waste released through anus 

• Ammonia released through tube feet and skin gills 

reproduction

• Male or female 

• Egg and sperm released in water when other are detected 

• Larvae swims in the plankton community until they mature 

body plan

• Radial symmetry 

• Mouth is on oral surface, opposite is ABORAL surface 

water vascular system

• Opens to outside through a madreporite 

  • Madreporite connects to a tube called the ring canal 

  • From the ring canal, 5 radial canals extend into each arm 

  • Attached to each radial canal are hundreds of moveable tube feet 

• System operates like a series of hydraulic pumps 

  • When water is pushed in a tube foot, it expands 

  • When water is pulled out, the cup on the tube foot shrinks (vacuum) 

movement

tube feet

response

• Nerve ring that surrounds the mouth and radial nerve that connect the ring with body sections 

• Sensory cells detect food 

• Starfish have 200 sensitive cells (EYESPOTS) at arm tips 

• Statocysts  

ecological role

• Important carnivores that control population of other animals 

• Sea urchins control algae but can "overeat" and destroy habitats 

• Used by humans as a food source, chemicals as potential drugs against cancer and viruses 

• Sea urchins used to study embryological development (they are similar to us) 

• Death of echinoderms lead to increase of seaweed growth 

• Sea cucumbers provide habitats for parasites 

• Sea urchins bore into rocks and release nutrients

main characteristics

• Spiny skin 

• Radial symmetry 

• Internal skeleton 

• Water vascular system 

• Tube feet 

• Large variety