Phylum Echinodermata

Characteristics of Echinoderms

• sea urchins, sea cucumber and starfish

• triploblastic coelomate

• coelom occupies most of internal volume

• downward facing mouth

• upward facing anus

• pentaradial

• lost cephalization (through secondary evolution)

• bilateral → evolved to radial

  • larva are bilateral

• WATER VASCULAR SYSTEM

Water Vascular System

• used for transport, gas exchange, locomotion

• pore called madreporite → regulates amount of water in vascular system

• madreporite leads to central canal which branches into 5 radial canals with lateral cavities called ampullae, with tube feet

• tube feet → locomotion and capturing food

• regulate how much water is in ampullae - how much tube feet can be extended/retracted along with muscles to move them

Dermal Skeleton

• skeleton is made of caco3 plates and spines

• spines - Spicules, can allow for movement or can be fused to plates and be inflexible

• endoskeleton as it is enclosed by the epidermis

Echinoderm Classes

• Asteroidea

• Echinoidea

Asteroidea

• starfish

• dorsoventrally flattened

• 5 arms extending radially in 5 directions

• spicules are not fused - flexibility

• carnivorous or omnivorous

Echinoidea

• sea urchins

• globular or discoid shape

• spicules are fused - inflexibile

• conspicious spines

• complex jaw apparatus called - Aristotle’s Lantern

• herbivorous