Pentamerous
Toothpick
Porcupine
Dome
Feet
Spine
Mouth
Nose
Both intertidal area and subtidal areas
On the beach
Subtidal area only
Intertidal area only
Because sea urchins have large numbers of eggs
Because a sea urchin's egg is relatively big
Because sea urchins have large numbers of relatively big eggs
Because the eggs make great omlettes
Other sea urchins
Sea cucumbers
Small fish
Algae
Animalia
Echinoderms
Strongylocentrotus
Purpuratus