The classic seasnake: fast, dangerous, agressive. The most members of it's family are hunting in the deep, but Navivenator (ship-hunter) comes often to the surface... and encounters with humans are unavoidable...
large prey is sometimes constricted, but mostly they use their teeth to kill. Seasnakes that live in groups hunt often like killerwhales, the others more like sharks (coming fast from the deep and make a big fat bite)
I like how you gave the seasnake a monitor-like tongue. I guess it would make sense that their close relatives would have the same tongue. Definitely would help in the ocean depth.
Oh and I'm wondering, with their fearsome reputation of being ship wreckers, are these guys fairing well in present day? For some reason I feel that any sailor would go out of their way to kill Navivenators.