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