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