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