What was that thing??? It was green and has scary looking teeth. Full length of this species is about 4 feet if you could see it outside of its hiding place. These animals are nocturnal though. I have seen one during a night scuba diving trip. It was freely swimming in the open all around hunting the reef fish. HUGE! Here is a picture of one that I took two years ago in Cayman when I was diving on the west side off Seven Mile Beach. You can see more of its body.
We also saw a spotted species of this animal but could not get a good photo or video. They are smaller but are really cool looking too.