As many have said, it has a sort of dinosaur look to it as far as pose go. I'd say Raptor would be more appropriate for its size than trex.
What does it look like while swimming? That might help make a more accurate name.

I'd definitely say something simple is best, since most of the names thus far are fairly simple and self explanatory.

Call it the mantis lol

I'd call it something like the muck raptor or something, something that sounds like slang, it is being named by sailors after all.

Maybe you could call it a crawdad, as a callback to the older version.

Edit: Maybe something like Sea Devil? It really doesnt seem to be analogous to anything earthly.

Not sure if I'm late to the naming game, but perhaps Rendercraw? Or Bilge/Scumwalker? Lesser Vagrant? I do want to mention that the legs strike me as a bit odd, as I feel like the back and front (from the side perspective) legs should be swapped with the fleshy, muscular parts facing the center mass, and the hardened armored bits decorating the outside like the rest of the body. Might've just been an error when putting the sprite together or intentional but wanted to point it out.

How about snatcher
This thing looks like i would break through the windows in your sub and yank you outside to eat ya.