Seriously, they're worse than chryssalids, they're FLOATING chryssalids :/
*edit* Guess it does require some in-game lore to understand why exactly this is scary... I'll try to explain:
- The aquanaut who's just been impaled through the face will become a shambling, mindless zombie next turn, and when killed will spawn another tentaculat;
- The guy who's shooting the torpedo is most probably going to miss, and even if he doesn't, it's not going to do much :D
- The third one's pretty much panicking by now. Lose her turn, gets zombified.