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