phylum echinodermata "spiny skin" strangest group in animal kingdom closest invert...

Phylum Echinodermata"Spiny Skin"

Strangest group in animal kingdom

Closest invert relationto the Chordates

Endoskeletonjust under skin

Lack sensory organs

No brain

No clear excretoryor circulatory systems

Phylum Echinodermata"Spiny Skin"

Possess water vascular systemfor movement and feeding

Larval stages are bilaterally symmetrical

Undergo metamorphosisto become a radial adult

Sea stars, brittle stars, sea urchins, basket stars, sea cucumbers, sand dollars

Class EchinoideaSea urchin

Sand dollar

Class Asteroideasea star

Class Holothuroideasea cucumber

Class Ophiuroideabrittle star

Body Plan - External Anatomy

Body Plan - External Anatomy

Madreporite Plate

Sensory Tentacles

Spiny Skin

Body Plan - External Anatomy

Body Plan - External AnatomyOral View

Dermal Spines

Tube Feet

Peristome

Mouth

Internal AnatomyLack many common organ systems

Nervous SystemDecentralized nervous system with: 1) central ring of ganglia 2) nerve net 3) radial nerves

Amazing ability to regenerate arms and some organsAutotomy - can intentionally lose an arm to avoid predation

Water Vascular SystemUsed for locomotion, feeding, waste removal and respirationSystem composed of canals connecting tube feetWater enters through Madreporite, then passes through stone canal to ring canalHydraulic system allows for powerful but slow movement

RespirationClass Holothuroidea - use respiratory tree

Class Asteroidea - use combination of gills and tube feet

Digestive System

Complete systemFood travels from mouth to cardiac stomach to pyloric stomach, to intestine to anusCan continually digest and ingest food

Reproductive SystemSeparate sexes but impossible to tell differenceGonads present in arms

Life CycleBilateral larva --> Metamorphosis --> Radial Adult