Complex sentence: Sea butterflies, also known as Thecosomata or flapping snails, are a taxonomic order of pelagic swimming sea snails, holoplanktonic opisthobranch gastropod mollusks in the order Thecosomata (Blainville, 1824).
Split into simpler sentences: Sea butterflies, also known as Thecosomata or flapping snails, are a taxonomic order of pelagic swimming sea snails. These are holoplanktonic opisthobranch gastropod mollusks in the order Thecosomata (Blainville, 1824).