4. Echinoderms
Echinoderms means
“spiny skin”
Includes sea stars, sea
cucumbers, sea urchins
All are marine
Found on the bottom of
the sea
Pentaradial symmetry
Body parts arranged in
fives around an oral-
aboral axis.
5. Skeletal system
Endoskeleton: skeleton found
within the tissues
It is always covered by a thin
layer of tissue. Spines and
bumps give reference to their
name which means “spiny-
skinned”
Has a water vascular system for
movement and structure
Network of canals in which sea
water circulates throughout the
body
6. Respiratory system
• Respiratory system is not well defined
• Contain tube feet and skin gills for respiration
• Respiration also carried out by the water
vascular system
7. Circulatory system
No circulatory system
True heart and blood are absent
The coelom is adapted into a water vascular
system that circulates nutrients, blood and gases
8. Nervous System
Nervous system contain nerve cords
Echinoderms lack a brain, but they make up a simple system
of scattered nerve cells around their body which can sense
light, gravity, and chemicals released by potential prey
Tube feet works as sensory structures
9. Digestive system
Contain complete but simple digestive system
Mouth stomach intestine anus
Mouth and stomach can extend outside of the body
Digestive enzymes located in glands that extend into
the arms
10. Reproduction
Reproduce sexually
Regeneration occurs if lost an
arm or guts
Echinoderms reproduce by
external fertilization
Both types of gametes are
excreted into the open water
where fertilization occurs
Larvae can freely swim around
before settling into the sea floor
to mature into adults
12. Asteroidea
Includes sea stars or starfish
Most have 5 arms from a
central disk, though can have
up to 50
Each arm carries an equal
share of organ systems
The anus is on the aboral (top)
side
Hundreds of tube feet are
found in channels called
ambulacral grooves radiating
from the central disk
13. Ophiuroidea
Includes brittle stars
Legs proportionally longer, thinner and flexible than sea starts
Organs in central disc
Tube feet lack suckers
Eat particulate matter on the ocean floor
14. Echinoidea
Includes sea urchins and
sand dollars
Body structure forms a
round, rigid body with
movable spins and
pedicellarie
Locomotion achieved by
movable spines
Grazers – feed on algae and
dead organic matter
15. Crinoidea
Includes sea lilies and feather
stars
Sea lilies have a long
stalk with branching arms that
attach them to rocks and the
ocean bottom
Feather stars can detach and
move around
Mouth & anus on upper sarface
16. Holothuroidea
Sea Cucumbers
Elongated body, stretched
out from mouth to anus
Tough skin supported by
calcareous spicules
Tube feet near the mouth are
modified into tentacles for
feeding
Some burrow and capture
food while others ingest
sand and filter out detritus
and small organisms