Phylum Echinodermata
Phylum Echinodermata (spiny skin)
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Sea stars, sea urchins, sea cucumbers
Pentamerous radial symmetry
Oral/aboral sides (anus), no brains
Endoskeleton
Water vascular system that extends to muscular
tube feet (madreporite pulls in H2O)
• Tube feet end w/ sucker for attachment,
movement and receiving stimuli
Sea Stars/Starfish
• Five arms from a central disk usually
• 100’s tube feet in ambulacral grooves, slow
moving, gas exchange
• Endoskeleton made of interconnected CaCO3
plates for flexibility
• Spines like mini-pincers (pedicellariae)
http://www.youtube.com/watch?v=A100m5Ep
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Nervous System
• Nerve net similar to cnidarians (no brain)
– Coordinates movement of tube feet and spines
• More complex behavior
– Rightning of body
– http://www.youtube.com/watch?v=44iw5FvYb7s
Feeding and Digestion
• If prey is bigger than mouth, flip stomach
outwards and release digestive enzymes
• Prey on bivalves, gastropods, barnacles
Reproduction (Sexual)
• Timed spawning (Sexual)
• Larvae are bilaterally symmetrical
Reproduction (Asexual)
• Can separate central disk or body into two
pieces (sea stars, brittle stars, sea cucumber)
• Regeneration- ability to grow lost or damaged
body parts
– Needs part of central disk in most cases
Sunflower star
• Up to 24 arms
• Moves at 1m/min
• 15,000 tube feet!
Brittle Stars
• 5 arms, longer, flexible, sharply demarcated
from central disk
• Tube feet without suckers
• Lack anus
Feather Stars
Crown of Thorns Starfish
• Menace to coral reefs
• One of the poisonous varieties of echinoderm
Sea Urchins
• Round, rigid endoskeleton (test), movable spines,
pincers, tube feet along body
• Mouth on bottom (Aristotle’s lantern), anus on top
• Feed on seaweeds, detritus
• Sand dollars have flat bodies, short spines
– Deposit feeders
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Sea Cucumbers
No spines, no test (calcareous spicules only)
Elongated body plan
5 rows tube feet extending from mouthanus
Deposit feeders- feeds on organic matter
Burrow often
• Defense: discharge sticky, sometimes toxic,
substance. Some expel organs from
mouth/anus to distract (evisceration)
• http://www.youtube.com/watch?v=wXf_Yod
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