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