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Echinodermata
“The spiny skinned animals”
Echinoderms
•
The spiny skinned animals include these
Classes:
1.
2.
3.
4.
5.
Class Crinoidea - the crinoids or “feather stars”
Class Asteroidea - starfish (sea stars)
Class Ophiuroidea - brittle stars, basket star
Class Echinodermata - sea urchin, sand dollar
Class Holothuroidea - sea cucumbers
Starfish (Asteroidea)
• Carnivores – clams,
mussels, bivalves
• Motile by way of tube
feet
• endoskeleton made of
calcareous plates (ie.
Calcium carbonate)
• breathes through
dermal “skin gills”
Starfish arm
• Each arm contains a digestive gland and
gonads
• The top of the tube feet are called ampulla,
like a medicine dropper that is squeezed to
create pressure
• Arm will regenerate if torn off = Asexual
Reproduction – fishermen learned this the
hard way 
Starfish
• The eye of the starfish is at the end of the
arms. (It is often red coloured)
• The anus of the starfish is on the top (aboral
side)
• The mouth piece of the starfish is called
“Aristotle’s Lantern”.
Tube Feet
and Mouth
Star fish
• The water vascular
system’s opening is
called a madreporite.
It opens into a radial
canal. The radial
canal then goes out to
the arms in radial
canals. The radial
canals then feed water
to the tube feet.
Anus
Ring Canal
Digestive Gland in Arm
Crinoids
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Filter feeders
some are sessile
some are motile
They were very
common in the
Paleozoic
• Their bodies are often
found in limestone
deposits
Crinoid Arm
Brittle Stars
• These are perhaps the fastest of the
echinoderms.
• Most of them are filter feeders or detritus
eaters
• Flexible arms, and may be offered as food
to get away from predators
Basket Star
Brittle Star
Echinoidea
• Lack arms
• eat algae or are
detritus eaters
• usually have spines
• Gonads prized for
sushi – Bleecker tried
this one as a dare and
hated it!
Sea Cucumbers
• Detritus eaters – the
vacuum cleaners of the
sea
• do not have skeletal
parts
• will eviscerate if they
are scared, meaning
offer up internal
organs as food to
distract predator
Quick Notes on Echinoderm Systems
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Major Body Systems
Digestive – external digestion by lowering
stomach onto prey and releasing enzymes which
are absorbed.
–
Carnivorous Starfish consume such common prey
as…
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Snails
Corals
Other echinoderms
Herbivores such as Sea Urchins consume Algae off
rocks
Filter feeds are Brittle Stars and clean the ocean floor
– eg. Brittle Stars
Respir/Circulatory
•
Respiration – use of thin walled Tube Feet act as
diffusion sites for resp. and also skin Gills in
some species.
•
Circulatory – due to Simple body plan, and
efficient Digestive system, nutrients are carried
throughout the body. Circulatory system is not
Needed.
Excretory/Motility
•
Excretion – wastes pass out the Tube Feet. Nitrogen
wastes excreted as Ammonia, out the Anus.
•
Sensory/Nervous – no Cephalic development. Starfish
have up to 200 Light sensitive cells clustered in EyeSpots
of each arm. No actual eyes. For balance and hearing,
Statocysts or tiny stones pass over hairs to tell the starfish
up from down and sense motion or sound by vibrations
in the water.
•
Movement – water pumps system with Tube feet. Suck
Water in or out to grasp or release and move.
Reproduction
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Reproduction – echinos are either Male or Female. Sperm
and eggs produced in the Testes or Ovaries. Symmetry of a
starfish is Radial in adults, meaning if you cut it into a
Chunks or many pieces, each slice is the same. Except, in the
starfish larvae, they have Bilateral symmetry, just as in
advanced critters like Mr. B – okay not that advanced , but
you know, they’re trying, okay…
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Asexual Repro – ask a Fisherman and s/he will tell you that
tearing starfish into chunks is a great way to Increase their
population. Each chunk will undergo regeneration and form
new starfish. So, ripping them up is not a great way to reduce
predation on Shellfish, which bring in a pretty-penny.