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Means = spiny skin Examples: Sea Stars, Sea urchins, Sea cucumbers, Sand dollars, Sea Biscuits

Sea stars

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Sun star Brittle Star

Basket Star Crown of Thorns

picture of Patrick here

Sea stars

Sea Urchins

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Sand dollars

Sand dollars

Sea Biscuit

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Sea Cucumbers

1. Body Structure

A. Eucoelomate (true coelom w/ peritoneum) B. Similarities to Chordates

1. Deuterostome Embryonic development (mouth develops second) *

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*(NOTE: all animals covered before echinos. are protostomes i.e. mouth develops first)

2. Endoskeleton

a. thin layer of skin on top b. made of ossicles (hard bony plates) &

spines c. f(x) = support, protect

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C. Water vascular system

1. Series of connected canals filled with water 2. Water flow pattern:

madreporite (water intake) ►stone canal ►ring canal ►radial canal ►lateral canal ►ampullae & tube feet

2. Level of Organization – Organ system

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3. Symmetry

Adults - Radial (Sea stars mostly pentaradial)

Free swimming Larvae – bilateral

4. Habitat Marine

5. Feeding

a. Complete digestive tract (most complete so far ……..)

b. Two Stomachs + pyloric caecum

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c. Feeding Patterns

i. Carnivores – sea stars ii. Scavengers – sea cucumbers iii. Herbivores – sea urchins iv. Filter feeders – brittle stars

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d. Hydraulic feeding : sea star eats bivalve

o Tube feet inserted between shells o Bivalve adductor muscles tire, it opens o Sea star everts stomach into bivalve o Enzymes released to digest prey o Stomach absorbs dissolved bivalve o Sea star retracts stomach

★ No dorsal, ventral, anterior or posterior Mouth & Tube feet = oral side Anus (anal pore) & madreporite = aboral side

6. Respiration

★ diffusion across skin gills, + water vascular system

7. Circulatory System WVS

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8. Excretion WVS + diffusion across skin gills

9. Response No head, no cephalization Central ring of nerves around mouth Nerve branches in each arm

10. Locomotion – WVS Process = ★water into ampullae,

pushes tube feet down ★water out of ampullae pulls tube feet up

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11. Reproduction

Most dioecious Fertilization external

Regeneration – one arm & part of central disk

makes a new sea star (A problem for bivalve farmers!)

12. Ecological Roles

Predators Coral eaters – crown of thorns sea star Food – urchin eggs (sushi), sea cucumbers Medical research

– regeneration studies – embryology (sea star eggs are very large)

embryology similar to chordates

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1. Class Ophiuroidea – e.g. brittle stars

a. Arms are slender & sharply set off from central disk b. Move quickly (may throw down an arm and flee)

(autotomy) c. Scavengers & filter feeders

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2. Class Echinoidea – e.g. sea urchin, sand dollar,

sea biscuit

a. No arms

b. Central “shell” is fused ossicles = test

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c. Sharp (or stone) spines

3. Class Holothuroidea e.g. sea cucumbers

a. Elongated cylindrical body b. Reduced ossicles

c. Tube feet modified into oral tentacles for feeding,

Mucus traps food, detritus feeders

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4. Class Asteroidea e.g. sea stars

a. Mostly predators b. Eat plankton or bivalves

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