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