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