Echinoderms are marine invertebrates with pentaradial symmetry and endoskeletons covered by spiny skin. They include sea stars, sea cucumbers, sea urchins, and sea lilies. All have a water vascular system that circulates nutrients and gases in lieu of a true circulatory system. They reproduce sexually and regenerate lost body parts. Common phyla are starfish, which have 5 arms radiating from a central disk; brittle stars with long, thin legs; sea urchins with a round rigid body and movable spines; and sea lilies either attached to the ocean floor by stalks or free-moving like feather stars.

2. Animal Diversity: Invertebrates
by
Maryam Riasat
PHYLUM ECHINODERMATA

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

11. Taxonomic summary

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