Echinodermata
“spiny skin”
 Complete digestive system
 Some are carnivorous, scavengers
 Filter feeders, deposit feeders
5 Classes
 Asteroidea – starfish
 Ophiuroidea – brittle stars
 Echinoidea – sea urchin, sand dollar
 Holothuroidea – sea cucumber
 Crinoidea – sea lily
Asteroidea
 Starfish
 Arms extend from body, from central disk
 Majority have 5 arms, can have up to 40
 Some with structures called
pedicellariae. Claw shaped used to
remove organisms from settling on the
surface.
Circulatory system
 Open circulatory system
 Water vascular system. Transports oxygen through the
body.
 No heart.
Regeneration and Reproduction
 Can regenerate arms
 Some reproduce asexually
 Most reproduce sexually. Separate sexes
 Free spawners – release sperm and egg into water
Nervous system
 Nervous system allows for sensing the
environment
 Sensory cells – sense light, contact,
chemicals, and water current
Feeding and Digestion
 Scavengers and carnivores
 Feed on snails, clams, oysters, sand dollars
 Complete digestive system
 2 stomachs : cardiac stomach and pyloric
stomach
 Grasp prey with arms, evert cardiac stomach
and secrete enzymes on prey to digest then
suck them up
Class Ophiuroidea
 Brittle stars, basket stars
 Not true sea stars but have similar body
plan
 The arms can measure over 3 feet across
 Can live in tide pools to deep sea
 Live in cold and warm water
Reproduction and Regeneration
 Mostly reproduce sexually
 Asexual by division or regeneration
 Can regenerate lost limb
 Feed on small organisms or can filter feed
 Nervous system similar to starfish
 Have no eyes only sense organs
 Some can change color
Class Echinoidea
 Sea Urchin and Sand dollar
 Sea urchin spines – some are barbed and
some are hollow with venom
 Sea urchins that have venom – dangerous
to predators and swimmers
Reproduction
 Separate sexes
 Release sperm and egg into water
 Some female sea urchins brood young
externally
 Most sand dollars have separate sexes but
some are hemaphrodites
Feeding and Digestion
 Sea Urchin – herbivores, deposit feeder
 Feed on algae
 Well developed digestive system. Can process
indigestible materials
 Sand dollar – mouth and anus on the same
surface (aboral surface)
 Bury into sand allowing only mouth exposed
to water current
 Filter feeder
 Capture particles by sticky mucous on tube
feet.
Class Holothuroidea
Sea cucumber
Found all over the world
Range in size 3cm to 1 m long
Look like a worm
10 to 30 tentacles surrounding mouth
No skeletal structure. Body wall of muscle for
support
 Slow moving
 Defense – ejecting intestines to confuse
predators
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Reproduction and feeding
 Only sexual reproduction
 Most fertilize externally
 Few with internal fertilization and
development
 Some brood eggs in the tentacles
 Deposit feeders
 Trap particles on mucus covered tentacles
and push into mouth to ingest
Crinoidea
 Sea lily, feather star
 Smallest class
 Common on coral reefs
 2 body regions: 1) calyx – most organs
contained. 2) Rays – use for feeding
 Both mouth and anus found on oral surface
 Filter feeders
 Sexual reproduction
 Regenerate lost body part
Economical Importance
 Starfish – use as lime for farmers
 Brittle star – once as food source, now
more ornamental
 Sea urchin – used for food, sushi
 Sand dollar – ornamental
 Sea cucumber – food and medical
properties (cancer and arthritis)