I am a water animal and I look like a star. Who am I?

I am an aquatic animal with blue blood. Who am I ?

Water animal covered by a hard shell . They tuck their head inside their shell to protect themselves from enemies.

Which water animal is bigger than the elephant ?

Animals that live on land and water are called ________

Can you name a water animal that walks faster sideways?

Which water animal does not have a heart or a brain?