Download Ch 40 Echinodermata

Echinoderms
Phylum Echinodermata
 Echinodermata means “spiny skin”
 Echinoderms range in habitat from
shallow coastal waters to deep ocean
trenches
 Vary in size from 1 cm to 1 meter
 Organisms in this class include:
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Sea stars
Sea Urchins
Sand dollars
Sea cucumbers
Characteristics
Fossil record dates back 500 million years
Ancestors were sessile, most species later
evolved ability to move
Deuterostomes
blastopore develops into anus, mouth is
secondary
Makes them more closely related to Chordates
Characteristics
Radial Symmetry
Similar to cnidarians, have no sign of cephalization
However, they develop from bilaterally symmetrical free
swimming larvae (probably a sign of ancestry)
Most have pentaradial symmetry
Body parts extend from center along five spokes
 Three other major unique characteristics
 Endoskeleton made up of calcium carbonate
plates called ossicles
 Water-vascular system
 Tube feet
Taxonomists have divided
7,000 species of
echinoderms into five
classes:
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 Crinoidea
 Asteroidea
 Ophiuroidea
 Echinoidea
 Holothuroidea
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Crinoidea
(“lily-like”)
Include:
Sea Lilies: Most closely resemble fossils
sessile as adults
Have long stalks that attach to rocks or the ocean floor
Feather stars: can swim or crawl, but may stay in place
for long periods
 Five arms extend from body and then branch
Sticky tube feet that are at the end of each arm
filter food and serve as a respiratory surface
Mouth faces up
Crinoidea
Ophiuroidea
(“snake-tail”)
 Largest echinoderm class (2,000 species)
 Basket stars: thin, flexible arms. Branch to form
coils that look like tentacles
 Brittle stars: thin arms that break of easily and
regenerate
 Primarily reside under stones & in crevices and holes of
coral reefs
 Some feed by raking food off the ocean floor with their
arms and tube feet
 Others trap suspended food with mucous strands
between their spines.
Ophiuroidea
Echinoidea
(“spine-like”)
 Test: rigid endoskeleton that the internal
organs are compacted in
 Sea Urchins:
 Aristotle’s lantern: complex jaw-like mechanism
that are used to grind their food
 Include teeth that surround the mouth
 protection: barbs on their long spines that are
sometimes venomous
 Sand Dollars
 Found in sandy areas along sea coast
 Covered in short spines used for burrowing and
locomotion
Echinoidea
Holothuroidea
“water-polyp”
 Sea cucumbers
 Bodies are soft, armless
 Modified tube feet form fringe around mouth
 Feeding: tentacles around the mouth sweep
up sediment from the water
 Protection: some can eject internal organs
 Lost parts are later regenerated
 Process called evisceration
Holothuroidea
• https://www.youtube.com/watch?v=wXf_Y
odWw40
Asteroidea
(“star-like”)
 Starfish
 found all over coastal shores around
the world
 prey on oysters, clams, and other sea
food that is used by people
Structure &
Function
(Using the Starfish)
External Structure
 Typically have five arms, but some species have as
many as 24
 Oral surface: the underside of the body where the
mouth is located
 Aboral surface: top of the body (opposite the mouth)
 Body is covered in short spines that give it rough
texture
 Pedicellariae: tiny pinchers that surround each spine
 Protect and clean the body surface
Water-Vascular System
 Network of water filled canals connected to tube
feet
The path (figure 40-7)
Water enters through madreporite (sieve-like plate on
aboral surface
Stone canal (tube pathway)
Ring canal (tube that encircles mouth)
Radial canal (tube that extends down each arm)
Carry water to hundreds of hollow tube feet
Valves prevent water from flowing backwards
Water-Vascular System
 Upper end of each tube foot expands to form a
sac called the ampulla
Muscles contract around the ampulla forcing water
into tube feet and back out again
This is how the starfish can extend or shorten the
tube feet
Enable locomotion
Feeding & Digestion
 Mouth – esophagus –
cardiac stomach
 Cardiac stomach can be
turned inside out through
the mouth
 Transfers food to pyloric
stomach
 Connects to a pair of
digestive glands in each arm
 Most Sea Stars are
carnivorous
 Mollusks, worms, slow
moving animals
Other Body Systems
 No circulatory, excretory, or respiratory organ
systems
 fluid in coelom bathes organs & distributes nutrients &
oxygen
 skin gills: project through coelom lining; allow gas
exchange and waste excretion
 nerve ring: surrounds mouth & branches off into
nerve cords in each arm
 Radial nerve runs from ring down each arm
 If nerve is cut, tube feet lose coordination
 Eyespots: on end of each arm that responds to light
 Tentacles: responds to touch
Reproduction
 Most species have separate sexes
 each arm contains a pair of ovaries or testes
 Fertilization occurs externally
 Bipinnaria: free-swimming larva that a
fertilized egg develops into
 After ~2 months settles in the bottom and develops
into an adult through metamorphosis
 Regeneration:
 Process is very slow
 Use as a defense mechanism
 Can be used to reproduce asexually