These resemble floating lobster/centipedes. They make no movement sound and usually hid out in shallow water coves or deep water. Fairly slow movement speed but they have stunning bites that will knock you out after just one to two bites (fort: 20) and proceed to eat you alive while you smash your controller. A good technique to fight them is shoot them and run back a little then shoot (rinse and repeat). They drop chitin, silica pearls, and black pearls.
Be very careful about these-they do tons of torpor damage, I was down on the bottom of the ocean (on the island) and I saw a pack of these sea scorpions. I decided to dismount off of my mosa and kill them with my pick, as that would get more black pearls. When I got close to them one of them-a level ten hit me and knocked me out in one shot. I was level 88, wearing journeyman flak and apprentice riot. And they knocked me out in one hit. The moral of the story is that these things are very dangerous.