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