Phylum Echinodermata "Spiny Skin" Strangest group in animal kingdom Closest invert relation to the Chordates Endoskeleton just under skin Lack sensory organs No brain No clear excretory or circulatory systems

Phylum Echinodermata "Spiny Skin" Possess water vascular system for movement and feeding Larval stages are bilaterally symmetrical Undergo metamorphosis to become a radial adult Sea stars, brittle stars, sea urchins, basket stars, sea cucumbers, sand dollars

Class Echinoidea Sea urchin Sand dollar Class Asteroidea sea star Class Holothuroidea sea cucumber Class Ophiuroidea brittle star

Body Plan - External Anatomy

Madreporite Plate Sensory Tentacles Spiny Skin

Body Plan - External Anatomy

Oral View Dermal Spines Tube Feet Peristome Mouth

Internal Anatomy Lack many common organ systems Nervous System Decentralized nervous system with: 1) central ring of ganglia 2) nerve net 3) radial nerves Amazing ability to regenerate arms and some organs Autotomy - can intentionally lose an arm to avoid predation

Water Vascular System Used for locomotion, feeding, waste removal and respiration System composed of canals connecting tube feet Water enters through Madreporite, then passes through stone canal to ring canal Hydraulic system allows for powerful but slow movement

Respiration Class Holothuroidea - use respiratory tree Class Asteroidea - use combination of gills and tube feet

Digestive System Complete system Food travels from mouth to cardiac stomach to pyloric stomach, to intestine to anus Can continually digest and ingest food

Reproductive System Separate sexes but impossible to tell difference Gonads present in arms Life Cycle Bilateral larva --> Metamorphosis --> Radial Adult