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