1. Higher Invertebrates Echinoderms
Chapter 9
Higher Invertebrates Echinoderms

2. Echinoderms: Animals with Spiny Skins
Phylum Echinodermata
Include sea stars, sea urchins and sea cucumbers
Larval forms exhibit bilateral symmetry but most adults exhibit a modified form of radial symmetry
Mostly benthic, and found at nearly all depths
Sea cucumbers and brittle stars are commonly found in deep-sea samples

3. Echinoderm Structure
Endoskeleton: internal skeleton that lies just beneath the epidermis
ossicles: plates of calcium carbonate

4. Echinoderm Structure
Water vascular system: unique hydraulic system that functions in locomotion, feeding, gas exchange and excretion
passes through a system of canals
attached to some canals are tube feet

5. Echinoderm Sea Stars Class Asteroidea – sea stars
Typically composed of a central disk + 5 arms or rays
On underside, ambulacral grooves with tube feet radiate from the mouth along each ray
Aboral surface: the side opposite the mouth, which is frequently rough or spiny

6. Figure 9-42 SEA STARS.

7. Sea Stars Feeding in sea stars
most are carnivores or scavengers of invertebrates and sometimes fish
prey are located by sensing of substances they release into the water
sea stars envelope and open bivalves, evert a portion of the stomach, and insert it into the bivalves to digest them

8. Figure 9-43 SEA STAR FEEDING.

9. Echinoderm Ophiuroids
Class Ophiuroidea
e.g. brittle, basket and serpent stars
Benthic with 5 slender, distinct arms, frequently covered with many spines
Lack pedicellariae and have closed abulacral grooves
Tube feet lack suckers and are used in locomotion and feeding
Brittle stars shed arms if disturbed

10. Figure 9-44 (b) BRITTLE STARS.

11. Echinoderm Crinoids Class Crinoidea–sea lilies and feather stars
Primitive, flower-like echinoderms
Most are feather stars, which seldom move and cling to the bottom with grasping cirri
Suspension feeders
Can regenerate lost arms

12. Figure 9-49 (a) CRINOIDS.

13. Figure 9-49 (b) CRINOIDS.

14. Echinoderm Sea Urchins
Class Echinoidea Body enclosed by test—a hard exoskeleton
Benthic on solid surfaces (sea urchins) or in sand (heart urchins, sand dollars)
Regular (radial) echinoids: sea urchins; spheroid body with long, moveable spines
Irregular (bilateral) echinoids: heart urchins and sand dollars; have short spines on their tests

15. Figure 9-45 (a ) ECHINOIDS.

17. Echinoderm Sea Cucumbers
Class Holothuroidea
Have elongated bodies, and usually lie on 1 side
Respiratory trees: a system of tubules located in the body cavity which accomplish gas exchange
Sexes are generally separate

18. Figure 9-47 (a) SEA CUCUMBER.

19. Ecological Roles of Echinoderms
Spiny skins deter most predators
Predators of molluscs, other echinoderms, cnidarians, crustaceans
crown-of-thorns sea star eats coral
sea urchins destroy kelp forests
Black sea urchins (Diadema antillarum) control algal growth on coral reefs
Sea cucumber poison, holothurin, has potential as a medicine