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