Download Echinodermata - Part 1 - Ms. Marcos` Biology Wiki

Phylum Echinodermata
“spiny” “skin”
www.onacd.ca
Sea stars
Sea cucumbers
Feather stars
Sand dollars
Sea urchins
Brittle stars
Major Classes of Echinoderms
ECHINOIDEA: Includes
the sea urchins and
sand dollars
ASTEROIDEA: includes
the starfish
HOLOTHUROIDEA: includes
the sea cucumbers
OPHIUROIDEA: includes the
brittle stars
(below: a fossilized brittle star)
CRINOIDEA: includes the
feather stars
Characteristics of Echinoderms
• Pentaradial symmetry
• Have a calcareous skeleton inside
their body (endoskeleton)
• Complete digestive system
• Open/reduced circulatory system (no
heart) with a central ring and vessels
• Simple radial nervous system (no
brain)
• Reproductive system consists of
gonads which take up a significant
amount of space in the body cavity
• Sexual reproduction with fertilization
outside body (most)
• Have ciliated, free-swimming larvae
• Possess a water vascular system
used for gas exchange, feeding and
locomotion
Taking a closer look at Sea Stars
• Possess 5 or more arms
•
•
•
which radiate from a central
disk
Mouth is located on oral
surface (underneath)
Found all over the world
(very diverse!)
Most possess a simple light
sensitive eye spot at the end
of each arm
Sea stars
• Spiny projections on
the arms
• Tube feet underneath
the arms grip objects,
move, and gather food
• Water vascular
system – moves the
tube feet
The Water Vascular System
• A central ring and a series of canals that
eventually end in tube feet.
• Tube feet are used for movement, feeding and
bringing in water for gas exchange.
• Water vascular system:
– Water enters through the madreporite
– Ampulla on the top of the tube foot
squeezes water into the tube, making it
longer
– To pull the foot back, the ampulla refills
with water, making the foot shorter
Tube feet of a sea urchin!
Using muscles to force water into the tube feet extends
and pushes them into the ground.
The muscles are then relaxed in order for the tube feet
to retract.
Digestion
•
Most are predators
How to eat a clam
(like a sea star):
1. Pry apart the two
shells using your
tube feet
2. Eject your stomach
through your mouth
into the clam
3. Digest it inside the
shell
4. Pull your stomach
back inside.
Mmmmm!
• Defenses:
– Pedicellaria, tulip-like pincers that can inject a
painful venom
– Incredible powers of regeneration – can regrow
all arms if the central disk remains
• Reproduction – They are Dioecious Animals!
– Asexual - split in half
– Sexual - mass spawning events
Normal Sea Star
Mutant Sea Star?
Mutant?
Not all sea stars have 5 arms…
Sunflower and sun stars have many more.
Crown of Thorns Sea Star
• Predator of coral polyps
• Explosions in crown of thorns populations
have devastated some coral reefs
Feather, brittle and basket stars
• Suspension
•
feeders
Arms transfer
plankton from
the water to
their mouths
Basket stars are nocturnal and curl up
their arms during the day
Basket Star
Brittle Star
► Will
voluntarily break off an arm to escape
predation
► Move quickly (for a sea star)
Feather Stars and Sea Lilies
Feeding arms on a feather star
There may be 5 to 200 arms on a
feather star (no tube feet here!).