Echinoderms

“spiny skin”

Echinoderms: Main Characteristics

• Spiny Skin – Exoskeleton – Musculoskeletal

• 5 part radial symmetry – Penta-radial

• Tube feet: Movement– Water-vascular system

• Benthic organisms

Classes

• Asteroidea: Sea Stars• Ophiuroidea: brittle

stars • Echinoidea: sea urchins

and sand dollars • Holothuroidea: Sea

cucumbers • Crinoidea: Sea Lilies and

feather stars

Class Asteroidea: Sea Stars

• Aster = star, oides = in the form of

• Large Coelome• Circulatory system: – use diffusion & cilia to

move gas, nutrients and waste

• Respiratory system: – Dermal branchi on skin

Diagram the arm of the starfish

Asteroidea

• Digestive System: – Mouth on underside– Opens into cardiac

stomach • Folds out of body into prey

to secrete enzymes

– Opens into the pyloric system • Nutrients diffuse out of the

pyloric stomach

• Eat: – mollusks, crustacheans,

polychaetes, coral, detritus

The Water Vascular System

• Who can explain how hydraulics work? • Water Vascular System:– Made up of a series of water-filled canals that run

down the arms from a canal ring in the center • Radial canal – ampullae – tubed feet

Water Vascular System

Asteroidea vs. Ophiuroidea

• Sea Star vs. Brittle Star• Sea Stars: – Arms attached to arms – Carnivores: Active

Predators

• Brittle Star– Arms NOT attached to

arms– Not active predators: eat

plankton

Echinoidea: Sea Urchins

• Same structure, longer spines than starfish – Move by means of tube

feet

• Feeding – Herbivores, feed on algae

and marine plants – Grazers – Scrape food using

ARISTOTLES LANTERN!

• Roles: – Control algae

Sea Cucumbers

• Elongated Body Plan – Long sea urchin

• Tube feet to move • Separate sexes • Take organic nutrients out

of sand – Use oral tentacles

• Defense: – release internal organs– Tubules called cuvierian

tubules: sticky and poisonous

CFU

• What is the etymology of Echinoderm • What is the organ called that extends and

contracts echinoderm’s tube feet? • What kind of symmetry are Echinoderms? • What is a major difference between the feeding

habits of starfish and sea urchins? • What is the major difference between sea stars

and brittle stars • Explain how sea cucumbers defend themselves.

Why are they able to do this?