The wonderfully irreverent site www.godchecker.com/ added:
"DYLAN: As a Sea God, he didn't make much of a splash. The son of GWYDDION and ARIANRHOD, he leapt from mum's arms straight into the sea. Sometime later his uncle, a Smith God called Govannon, killed him. The waves sighed. Sometimes they still do."
The more serious site, www.pantheon.org/mythica.html said:
"Dylan ("sea"), a virgin-born son of Arianrhod. He was a sea-creature, and returned to the waves. Much later, he came back upon land and was killed by his own uncle Govannon, who did not know who he was."
Poor Dylan, what a sad tale. So many legends seem to involve people being killed by their friends or family because they didn't know who they were.
I am sure there is a lesson to be learnt from Dylan's story somewhere, even if it is just to be careful about what seafood you eat...