The Sea Dragon Leviathan has arrived to ruin your underpants!
Come across it earlier. Wandering around the lava biome with my PRAWN. It's nasty. I found my first crimson ray down there too. I actually enjoyed finding that more.
The crab squid things are brutal now though. They have an EMP pulse or something that temporarily knocks out your seamoth. The thing is strong enough to completely destroy your seamoth quite quickly as well, and they're generally at depths where swimming to the surface isn't an option if your ride gets totaled.
I really really hope they add mod support for this game on final release.