They are highly poisonous. Think... Troodon of the sea. Using a good leveled tame to kill these can be very useful though, as you get loads of chitin, some silica pearls, and black pearls!
I think it should be ride able like the scorpion dino but makes it so you can breath underwater without scuba gear and I hope if this happens... wildcard don't make it like the giga. "I'll follow you to texas"
Normally I see their shadow but when I get closer it disappears into seaweed but I found a way to stop this. Dismount your ichthyosaurus or tusoteuthis and these guys will start showing up. This mean easy black pearls!!!!!