I know Anet take a lot of inspiration from mythology and folk legend for Tyria but there arn't a lot of sea monsters with specific names beginning with S. Scylla is a possible choice or a variation/extension as she had multiple heads and our deep sea friend is shown to be hydra like in his concept art but, the she is the pesky bit. All Elder Dragons so far seem to have a very male presence, they don't reproduce in the traditional sense... apart from Mordremoth who may have birthed the pale trees from seeds but that's a whole other conversation. Then there are Selkies and Sirens, also female creatures known for their trickery and murder mainly through leading young men astray. So I don't think the obvious options are very likely.If we also look for clues in some other dragon names, it's possible his name will come from meaning or power.Mordremoth- It's quite close to Mordred from the Arthurian legends but I don't see much of a connection there, however in French Mordre can mean to bite orto encroach or to be tricked. Considering he is the dragon of the mind this fits quite nicely.Primordus- Obviously he is the first to awaken and the oldest so, primordial, first.Jormag- Might be taken from Jörmungandr which means huge monster or beast, although he was also a sea serpent so maybe that would have been better for Steve. I quite like the name Saegrund, in old english meaning the bottom of the sea.But who knows, the historian even says she thinks the letter is incorrect!