Phylum Echinodermata
Biology 11
Definition
 Echino- = “spiny”;
dermis = “skin”
Characteristics of
Echinoderms:
-spiny skin,
covering a hard
calcium
carbonate platelike
endoskeleton
Definition
 More characteristics of Echinoderms:
-water vascular system
-tube feet (suction-cup like structures)
-radial symmetry
-deuterostomes (blastopore develops into
anus)
-true coelomates
Body symmetry
 Echinoderms have five-part radial symmetry
 Their larvae, however, have bilateral
symmetry (like humans)
Form and Function
 Echinoderms have a water vascular
system, filled with fluid
 This system consists of canals that extend
throughout the body and opens to the
outside through a madreporite
Water Vascular System
 Madreporite connects to
ring canal, which
connects to radial canals
 Attached to the radial
canal are hundred of
tube feet
Feeding
 Use of tube feet to capture prey or plankton
 Can be herbivores (plankton)
 Can be carnivores (mussels, clams)
-ex. Sea stars can pry prey’s shell open,
push stomach out and pour digestive
enzymes into prey, then pull stomach
back in
Respiration and Circulation
 Thin-walled tissue of tube feet allow
respiration
 Skin gills (in some species)
 Circulation provided by water vascular
system (carries oxygen, food, wastes)
Excretion
 Solid waste through anus
 Metabolic waste (ammonia) through tube
feet and skin gills
Response
 Simple nervous system with no brain
 Have nerve rings around mouth, and radial
nerves
 Scattered sensory cells for light, gravity,
chemicals
Movement
 Use tube feet and muscle fibres attached to
endoskeleton
 Some have flexible joints or movable spines
Tube feet
Reproduction
 External fertilization
 Sexes are separate
 Sperm and eggs
released into water 
fertilization  larvae
 adults
Groups of Echinoderms - 1
 Class Echinoidea (Sea urchins and sand
dollars)
-have large solid plates that form a box
around their internal organs
Groups of Echinoderms - 2
 Class Ophiuroidea (Brittle stars)
-have slender, flexible arms that can be
shed to distract predators
Groups of Echinoderms - 3
 Class Holothuroidea (Sea Cucumbers)
-warty, moving pickles
Groups of Echinoderms - 4
 Class Asteroidea (Sea Stars – most
common)
-creep slowly on sea floor, carnivorous,
regenerative ability
Groups of Echinoderms - 5
 Class Crinoidea (Sea lilies and feather stars)
-filter feeders, long feathery arms
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The Starfish
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-Anonymous
Once upon a time there was a wise man
who used to go to the ocean to do his writing.
He had a habit of walking on the beach
before he began his work.
One day he was walking along the shore.
As he looked down the beach,
he saw a human figure moving like a dancer.
He smiled to himself to think of someone
who would dance to the day.
So he began to walk faster to catch up.
As he got closer, he saw that it was a young man
and the young man wasn’t dancing,
but instead he was reaching down to the shore,
picking up something and very gently
throwing it into the ocean.
As he got closer he called out,
“Good morning! What are you doing?”
The young man paused, looked up and replied,
”Throwing starfish in the ocean.”
“I guess I should have asked, why are you throwing starfish in the ocean?”
“The sun is up and the tide is going out.
And if I don’t throw them in they’ll die.”
“But, young man, don’t you realize that there are miles and miles
of beach and starfish all along it.
You can’t possibly make a difference!”
The young man listened politely.
Then bent down, picked up another starfish and threw
it into the sea, past the breaking waves and said“It made a difference for that one.”
Comparing Invertebrates
Chapter 29
So many INVERTEBRATES….
how much do you remember?.....
Try not to look at your notes or
textbook and see how much you
know!
Evolutionary Trends
 Specialized cells, tissues, organs
sponges and cnidarians
little - none
flatworms
simple organs
mollusks and arthropods
organ systems
Evolutionary Trends
 Body Symmetry
Sponges
asymmetry
Cnidarians and
Echinoderms
radial symmetry
Worms, mollusks,
arthropods
bilateral symmetry
Evolutionary Trends
 Cephalization
Sponges and cnidarians
none
Most worms and
arthropods
ganglia
Certain mollusks
brain
Evolutionary Trends
 Coelom Formation
Sponges and cnidarians
Flatworms
Roundworms
Annelids
Mollusks, arthropods,
echinoderms
true coelom
none
none
pseudocoelom
true coelom
Evolutionary Trends
 Early Development
Sponges and cnidarians none
Worms, mollusks, and protostome
arthropods
deuterostome
Echinoderms
Feeding
 Simple:
 Complex:
Intracellular digestion
Extracellular digestion
-incomplete  complete
digestive system
sponges
Annelids, arthropods,
mollusks, echinoderms
 Both: cnidarians and flatworms
Respiration
 Diffusion
 Increase in specialized organs and surface
area
 Gills and book gills
 Lungs and book lungs, tracheal tubes,
spiracles
Circulation
 Closed circulatory
system:
-heartlike organ forces
blood through vessels
throughout body
Annelids, mollusks
 Open circulatory
system:
-heart pumps blood
through vessels into
sinuses
Mollusks, arthropods
Echinoderms: water vascular system
Excretion
 Aquatic invertebrates – diffusion
sponges, cnidarians, roundworms
 Terrestrial invertebrates
-nephridia – annelids, mollusks
-Malpighian tubules – insects, arachnids
Response
 Centralization
-nerve nets – cnidarians
 Cephalization
-ganglia – mollusks, arthropods
 Specialization
-eyespots, specialized sense organs to
detect light, sound, chemicals, movement,
direction of gravity, etc.
Movement
 Hydrostatic skeleton
-cnidarians, annelids
 Exoskeleton
-arthropods
 Endoskeleton
-echinoderms
Reproduction
 Asexual reproduction
-fragmentation, budding, division
 Sexual reproduction
-separate sexes, or hermaphrodites
-internal fertilization or external fertilization
The End!
Very good! How did you do? 