Phylum Echinodermata
(Echinoderms)
General characteristics
Invertebrates
Marine environments
not cephalized, no head
Deuterostromes (blastopore forms an
anus)
• Coelmates
• embryos have radial cleavage
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4 major unique characteristics
• 1- radial symmetry
– Often pentaradial symmetry, body parts extend from the
center along five spokes
• 2- endoskeleton made of ossicles- calcium carbonate
plates
– may be attached to spine
– Or spicules that protrude through skin, forms echinoderm“spiny skin”
• 3- water-vascular system
– Network of water-filled canals
• 4- Tube feet
– Small, movable extensions of the water vascular system
– Used for movement, feeding, respiration, and excretion
Evolution
• Fossil record dates back to more than 500
million years (the Cambrian period)
• Early echinoderms were sessile
• Only 80 species still sessile
• Now some can crawl slowly along ocean
bottom
• The bilaterally symmetrical larvae
resemble it’s ancestors
• Most closely related to chordates
Class Crinoidea
• means “lily-like”
• Five arms branch to form many more arms
• Mucus covered tube feet filter organisms from the
water
• Cilia then transport the organisms to the mouth
• Sea lilies
-Sessile adults
• Uses a long stalk to attach to rocks or the sea bottom
• Feather stars
– Can swim and crawl as adults
• Most species are extinct
Feather star –
Florometra serratissima
Class Ophiuroidea
• Means “snake-tail”
• Long, narrow arms allow them to move quicker
than other echinoderms
– Tube feet not used for movement
• Basket stars have thin, flexible limbs form coils that
look like tentacles
• Parts of brittle stars break off easily
– Can regenerate
Basket star –
Gorgonocephalus eucnemis
green brittle star –
Ophiarachna incrassata
Class Echinoidea
Means “spinelike”
Sea urchins and sand dollars
Test- rigid exoskeleton, encloses internal organs
Sea urchins have an Aristotle's mantle-complex jaw
like mechanism, aids in movement
Sand Dollar –
• Spines can contain poison
Echinarachnius exentricus
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Purple Sea Urchin –
Heliocidaris erythrogramma
Class Holothuroidea
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Means “water polyp”
Sea cucumbers
Armless
Live on sea bottom, use tube feet to burrow
Ossicles are very small and not connected, which
means their body is soft
California sea cucumber Parastichopus californicus
Class Asteroidea
• Starfish
– Carnivorous (mollusks, worms, other slow
moving animals)
– Can slowly pull clam apart
• use a cardiac stomach to begin digestion
• withdraws the stomach
• finishes digestion
Red-knobbed sea star- Protoreaster linckii
Sea Star digestion
Mouth
– Cardiac stomach- short esophagus
– Pyloric stomach
– Digestive glands (in each arm)
• secrete enzymes that break down food
– Nutrients go to the coelem
– Undigested material expelled through
anus
Sea Star
external structure
• The aboral surface (top half) is
covered in short spines
– rough texture
• Pedicellariae- tiny pincers that
surround the short stems
– keep the body free of foreign objects, ex.
Algae or other small animals
Sea Star Body Systems
--No circulatory system
– No excretory system
– No respiratory system
• Fluid in the coelem distributes nutrients
and oxygen
• Diffusion through skin gills on tube feet
(respiratory gases and waste)
– Skin gills- hollow tubes, stretch from
coelem to exterior
Nervous system
• No head= no brain
• Nerve ring instead (circles the mouth)
• Radial nerve runs from the nerve ring along each
arm
• Together coordinate tube feet movement
• Nerve net near body surface controls movement
of spines, pedicallariae, and skin gills
• Eyespot at the end of each arm responds to light
• Several tentacles and tube feet respond to touch
• Touch-sensitive and chemical-sensitive cells are
scattered all over the surface of the sea stars
body
Reproduction and development
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Most have separate sexes
Each arm contains a pair of ovaries and testes
External fertilization,
Larvae develops bilaterally symmetrical, called bipinnaria
Some retain their larvae in their body or among their tentacles
• Can regenerate arms, but it takes about a year
– Can shed an arm to escape a predator
• If an arm is attached to a portion of the central region, a
whole new organism can develop
• Some species reproduce asexually
– By splitting it’s body through the central region
Sea Star
Water-Vascular System
• Water enters through the sieve-like madreporite
on the aboral surface
• Passes through stone canal
• Then the ring canal
• Then the Radial canals
• Contraction of muscles
surrounding ampulla
cause the tube feet to
expand and contract
• Ends of tube feet act
as suction cups
• Allows the sea star to move
Works Cited
•
Charton, Barbara. "sea star." The Facts On File Dictionary of Marine Science, New
Edition. New York: Facts On File, Inc., 2007. Science Online. Facts On File,
Inc.http://www.fofweb.com/activelink2.asp?ItemID=WE40&SID=5&iPin=
DMSN1384&SingleRecord=True (accessed April 9, 2009).
•
"Echinoderms: Features." Animal Anatomy On File, New Edition. Copyright Diagram
Visual Information Ltd., 2003. Science Online. Facts On File, Inc.
http://www.fofweb.com/activelink2.asp?ItemID=WE40&SID=5&iPin=
A0439&SingleRecord=True (accessed April 9, 2009).
•
Edward J. Devillez, "Digestion (invertebrate)", in AccessScience@McGraw-Hill,
http://www.accessscience.com, DOI 10.1036/1097-8542.194500
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David L. Pawson, Andrew C. Campbell, David L. Pawson, David L.
Pawson, Raymond C. Moore, J. John Sepkoski, Jr., "Echinodermata", in
AccessScience@McGraw-Hill, http://www.accessscience.com, DOI 10.1036/10978542.210700