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