Sea Butterflies: The Fragile Beauties

Sea butterflies are very beautiful animals that are about the same size as the butterflies you know on land.  However, they are not at all related to land butterflies.  You would never guess what one of their closest relatives is.  It is a snail!  The sea butterflies look nothing like their relatives.  They have evolved differently to live their special life in the ocean.  Their shells have become much lighter to allow them to swim freely.  They have also become almost completely clear to camouflage themselves in the water.  Instead of using mucous to crawl like snails do, they use their mucous to create a large web for catching their prey.  Sea butterflies are very pretty animals to watch as they slowly swim through the dark ocean, but they are in danger.  Their shells are made of a special mineral called calcium carbonate.  The problem is that carbon dioxide can destroy their shells.  When humans burn oil or coal it makes it harder for the sea butterflies to stay safe in the ocean.