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