Mantis (Legacy)
From Official Barotrauma Wiki
Description
Mantis are golden horse-sized crustacean creatures named after their clawed forelegs.
In-game
Mantises are small enough to fit in the submarine's corridors, where they can move around quickly and attack the crew. On the other hand, their claws are inefficient against the hull, so they can only invade through pre-existing breaches.
Mantises can neither open doors nor claw their way out, so quarantining a section of the submarine where a mantis has been seen is a viable, if suboptimal, way to deal with it.
Trivia
Regalis confirmed that as of version 0.3.2.0, mantises are largely identical to crawlers, although they are meant to eventually diverge from them.[1]