1. Phylum: Echinodermata
The “spiny skins”……

2. General Information What kinds of sea life has a spiny or bumpy skin?
Body symmetry
All have radial symmetry
Usually can be divided into 5 parts or multiples of 5
This makes the body strong because the lines of fracture (weakness) don’t run directly across the body (see Fig 8-2)
All have a Nerve ring and a water vascular system
All have CaCO3 endoskeletons
The sizes range from microscopic spicules to visible plates
All are ocean-dwelling

3. Class: Echinoidea Means “like a hedgehog” Sea Urchins and Sand Dollars
Very common around the world and in a wide range of habitats
Some are very poisonous

5. Class: Echinoidea Skeleton Most are small enough to fit in your hands
Some have long, sharp spines and some have thick, blunt spines
Test – a hard skeleton made of CaCO3 plates
The test covers the soft internal organs & tissues
A very thin epidermis covers the test (making it an endoskeleton!)
Most of the plates have pores for internal, respiration organs to protrude through
Tubercles – ball and socket joints with muscles around the base
This is where spines attach
Ossicles – a complex series of up to 35 bones that the teeth attach to
Aristotle’s Lantern – all the mouth parts combined

7. Class: Echinoidea Reproduction Feeding & Digestion
Females release eggs into the water to be fertilized
Males release sperm into the water to fertilize the eggs
Fertilized eggs become free-floating larvae before settling to the bottom to become adults
Feeding & Digestion
Most urchins are herbivores
They scrape algae from the hard substrate with their teeth
Small bits of food move through a long digestive tube where they are digested and absorbed and indigestibles are passed out through the anus

8. Class: Echinoidea
Water Vascular System – a complex series of canals running throughout the urchins body used to help the urchin move
Madreporite – a sieve-like skeletal plate lying on the surface near the anal opening
Water – filled tubes (canals) open to the outside of the urchin through this plate
Tube Feet – tiny, delicate projections that are attached along the side of the radial canals
The tube feet are pushed out of openings in the test
Radial Canal – Long water-filled tubes that run up and down the urchin
Water enters and leaves these canals through the madreporite
The location of the amupllae
Ampullae –
These are valves that keep the water from flowing back into the canal
These valves control the tube feet