Serpents according to Wikipedia has many meanings but to this article simply means the name given to a snake in a religious or mythological context. But rather than religious this is reality:

These are the famous moray eels. There are many variety about a 100 species but these are the ones I managed to see in my limited diving experience. These nocturnal (most active at night) fish have a long, muscular, snake-like body.Fierce but gentle, these sea serpents will attack if one decides to disturb its peace. Some are venomous. But again they make the winning shots usually due to its ferocity.

Then, we have the Snails or the sea slugs better known as Nudibranch. I wrote about it earlier . Just to share some more pictures.