Feet
Mouth
Nose
Spine
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
Echinoderms
Purpuratus
Animalia
Strongylocentrotus
Small fish
Algae
Sea cucumbers
Other sea urchins
Toothpick
Porcupine
Dome
Pentamerous