Echinoderms

1. Echinoderms “Life with Spiny Skin”

2. A RadicalRadial Change • Worms, mollusks, and arthropods all have bilateral symmetry. • So do echinoderm larvae. • What kind of symmetry do adult echinoderms have? Bipinnaria larvae (sea star) Radial symmetry What other animal phyla display radial symmetry?

3. Five Alive • Most echinoderms show pentamerous radial symmetry. • This means there are usually five arms (or legs) or they are found in multiples of five. 2 1 3 5 4

4. Spiny Skin – but only the skin! • Echinoderm means “spiny skin.” • Echinoderms typically have: • well developed digestive tracts • well-developed coelom • Internal skeleton called an endoskeleton • Spines or bumps are anchored in the endoskeleton but may protrude through the skin.

5. What No Top and Bottom? Echinoderms have no head; therefore, there is no anterior or posterior. • Rather than use the term dorsal, the side of the echinoderm without a mouth is called the aboral side. • The echinoderm mouth is usually on the bottom. This is termed the oral side. aboral oral

6. Water vascular system • A network of water-filled canals that function in movement, feeding, and excretion. • Water enters the echinoderm through the madreporite (mother pore) or sieve plate. • Water is then forced through individual tube feet allowing them to move.

7. Water Vascular System

8. Water Vascular System

9. Types of Echinoderms • Approximately 7,000 species – all marine • Located from the poles to the tropics • Five major classes • Asteroidea (sea stars) – not starfish –they are definitely not “fish” • Ophiuroidea (brittle stars) • Echinoidea (sea urchins and sand dollars) • Holothuroidea (sea cucumbers) – not a vegetable! • Crinoidea (feather stars and sea lilies)

10. Asteroidea • Endoskeleton rather flexible to allow for movement. • Most have five arms radiating from a central disk.

11. Asteroidea • Hundreds of tube feet are found in channels called ambulacral grooves radiating from the central disk.

12. Asteroidea • Naturally the anus is on the aboral (top) side. • Aboral surface covered with pedicellariae – tiny pincer like organs that keep the sea star clean.

13. Asteroidea

14. Ophiuroidea • Brittle stars • Most numerous class of echinoderms. • Characterized by thin, very flexible arms. • Eat particulate matter on the ocean floor. • No anus. • Often hidden. Ophiothrix spiculata

15. Ophiuroidea

16. Echinoidea • Sea urchins & sand dollars • Endoskeleton is a rigid, shell-like “test.” • Covered with movable spines – used in locomotion and defense. • Grazers – feed on algae and dead organic matter. aboral oral

17. Echinoidea • An intricate mouth and jaw system called the Aristotle’s lantern consists of 50 bones and is controlled by over 60 muscles.

18. Echinoidea • Not all “urchins” have prominent spines. • Sand dollars have flattened bodies and tiny spines. • They use a mixture of mucus and physics (Bernoulli’s principle) to capture food.

19. Holothuroidea • Sea cucumbers • Elongated version of the pentamerous body plan. • Lie on side with five rows of tube feet on bottom. • Tough skin supported by calcareous spicules.

20. Holothuroidea • 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.

21. Holothuroidea • Defense • Secrete toxins • Discharge sticky toxic filaments • Eviscerate – eject a portion of the internal organs to confuse an attacker. Sea cucumber evisceration

22. Crinoidea • Feather stars, basket stars, sea lilies • Suspension feeders • Oral surface on top • Can have from 5 to 200 arms! • Have claw like appendages that hold the aboral surface to the substrate.

23. Crinoidea