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