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PHYLUM ECHINODERMATA (means spiny skinned)

ex: seastars, sea urchins, sand dollars, sea cucumbers, sea lilies

Characteristics:

1. Radial (pentamerous) symmetry

2. Internal skeleton (endoskeleton)

3. Complete digestive system

4. Water vascular system with tube feet (hold or sense)

5. Highly regenerative - can eviscerate

6. Separate sexes; external fertilization

Seastars

2

PHYLUM ECHINODERMATA (means spiny skin)

ex: seastars, sea urchins, sand dollars, sea cucumbers, sea lilies

Why are they considered advanced?

1. endoskeleton of calcium carbonate plates

2. bilaterally symmetric larvae

3. water vascular system instead of muscles is a big advantage in predatory situations

4. highly regenerative - can regrow lost or damaged body parts

5. separate sexes; external fertilization

3

Why are they considered simple?

1. Light-sensitive eyes located at the end of each ray do not provide vision because there is no brain nor head.

2. They have reduced internal organs - no respiratory, circulatory, excretory. No nervous system.

4. Adults have pentamerous (5-fold) radial symmetry (associated with sedentary lifestyle)5. Respiration is by diffusion through the skin.

3. Nerve net (no nervous system) – exhibit complex behavior

4

Seastars are predators and eat a variety of organisms.http://www.youtube.com/watch?v=ALaMoS_vvNE

The seastar can open a clam shell a few millimeters wide.

Then by everting its stomach into the shell, the clam is digested and absorbed. http://www.youtube.com/watch?v=A100m5EpfFI Seastar Eating a Clam

Missing parts from injuries or evisceration are quickly replaced. Any portion of the central disk will regenerate a new seastar - a fact that oyster fishermen learned too late!

SEA STARS – ASTEROIDEA

5

Brittle stars have long flexible arms extending from a central disk

Brittle stars eat particulate organic matter

BRITTLESTARS - OPHIUROIDEA

Gray Brittle Stars (Ophiura luetkenii) on the move

6

Sea urchins use tube feet and spines to move

Sea urchins graze on seaweeds, seagrasses and algae

Mouth has complex system of jaws & muscles – Aristotle’s Lantern

SEA URCHINS- ECHINOIDEA

http://www.youtube.com/watch?v=gLK71-vsi2E

http://www.youtube.com/watch?v=D3W4OCnHyCs

7

Sea cucumbers are deposit feedershttp://www.youtube.com/watch?v=EvDYxvGx6k4 http://www.youtube.com/watch?v=vsLBOkYLLeI&feature=related

Some secrete toxic substances

Some expel their gut and other internal organs - evisceration

Missing parts from evisceration are quickly replaced

SEA CUCUMBERS - HOLOTHUROIDEA

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Crinoids are suspension feeders

Sea lilies are deep water

Feather stars perch and crawl on hard bottom shallow to deep water

Upside down brittle star

FEATHER STARS OR SEA LILIES- CRINOIDEA

http://www.youtube.com/watch?v=IFWeqDcAYGk

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SEASTAR DISSECTIONSeastar Dissection

Seastar External Anatomy

Seastar Anatomy Internal

Seastar Dissection