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