On the beach
Subtidal area only
Intertidal area only
Both intertidal area and subtidal areas
Algae
Other sea urchins
Sea cucumbers
Small fish
Echinoderms
Purpuratus
Animalia
Strongylocentrotus
Dome
Porcupine
Toothpick
Pentamerous
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
Mouth
Spine
Feet
Nose