1. Unit 6 Echinodermata
Sea Stars
Sea Urchins
Sea Cucumbers
Brittle Stars

2. Echinodermata (spiny + skin + to bear)
Phylum
Echinodermata (spiny + skin + to bear)
Echinoderms are an ancient species that began
evolving nearly 600 mya.
Fossil evidence shows that nearly 12 to 18 Classes have
gone extinct.

3. Adults Pentaradial; larva bilateral Calcareous exoskeleton
Characteristics of Echinodermata
~7000 species
All Marine
Pentaradial symmetry
Adults Pentaradial; larva bilateral
Calcareous exoskeleton
Water vascular system (locomotion, attachment, feeding)
Complete digestive tract
Nervous system
Close evolutionary relationships with Chordata
-both deuterostomes
Echinoderms evolved from a bilateral ancestor.
-Larva form still bilateral

5. Skeleton: Calcium carbonate plates called ossicles
Some ossicles are modified
into spines for defense.

6. Water vascular system: Sea water filled canals with
extensions on the ventral surface called tube feet.
Tube Feet:
Extensions of the
canal system used
for locomotion,
feeding and sensing
Environment.

7. 5 arm water vascular system

9. Class Asteroidea (star + in the form of)
~ 1500 species
Marine benthic (substrate) environments
5 arms radiate from central disc
Mouth center of ventral surface
Spines on aboral surface

10. Pedicellariae: Pincer-like structures on the aboral surface
Capture prey
Keep sessile organisms from attaching(sponge, coral)

11. Ambulacral groove: Several ossicles on the ventral
surface. Forms a groove that runs the length of the
arm.
-Paired rows of tube feet found in this groove.

12. Feed on gastropods, bivalves, crustaceans and coral.
Nutrition:
Feed on gastropods, bivalves, crustaceans
and coral.
2 stomach regions:
Oral stomach (cardiac)- larger, responsible for
beginning digestion.
Aboral stomach (pyloric) – smaller, gives rise
to digestive ducts, final
digestion and absorption.
-Some ingest whole prey
-Some digest externally
Excretion occurs through pores in the aboral surface as well as tube feet.

13. Nervous system: Nerve ring encircles mouth.
Radial nerves radiate to arms.
Sensory receptors in tube feet, especially
terminal feet.

14. Reproduction:
Asexual- Can completely regenerate from just one
section of an arm if it contains just a portion
of the central disc.
Sexual- Dioecious
Not Dimorphic
2 gonads in each arm.
Gonopores release
gametes externally.

15. Class Ophiuroidea ( Snake + Tail + in the form of)
Brittle stars
~2000 species. Largest of all Echinoderm Classes

16. Morphological differences:
Most between 1-3cm in size
Madreporite on oral surface
Use arms (modified ossicles) for locomotion
-not tube feet
Regeneration:
Autotomy (self + to cut) - can lacerate its own appendage
to escape predation, then regenerate.

17. Class Echinoidea (spiny + in the form of)
~1000 species
Sand Dollars live on soft sand or
mud.
Sea Urchins Live on hard surfaces

18. Urchin spines:
Spines may be hollow and contain venom.
Spines are hinged and movable.
Spines used to push Urchin, tube feet used to pull
Aristotle’s Lantern: Complex chewing apparatus with 35
ossicles and muscles.

20. Class Holothuroidea (Sea Cucumber + In the form of)
~1500 species
10-30 cm
No arms
Grow horizontally along oral-aboral axis.

21. Nutrition:
Elongated tube feet modified into tentacles
called “feeding tentacles”.
Crawl ocean floor collecting debris, digesting
organic material, eliminating inorganic waste.
Large ossicles form chewing ring around mouth

22. Respiratory trees: Branching tubes that carry sea
water throughout the body, absorbing O2 and
excreting waste.
Evisceration: Expulsion of respiratory tree, gonads,
and digestive tract. (sticky & toxic)
Organs regenerate

23. Class Crinoidea (lily + in the form of)
Sea Lilies
Feather Stars
~ 630 species
Most primitive - LCA of all Echinoderms
mya (early Paleozoic Era)

25. Calyx- a set of ossicles that
connect the crown/arms
with the stalk.

26. Class Concentricycloidea: (Having a common ancestor + Circle)
Sea Daisy
~1 cm in size
Unsure of precise ancestry to Echinoderms