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