For Thornmouth, I 100% agree with the octopus & owl mentioned above. Upon reading up on the guild again something else came into my head - while considering the symbolis of being a guiding light in the darkness I imagined an Albatross.
When I was younger I read Rime of the Ancient Mariner which told of a ship trapped in a storm. They crew see an albatross - which is a sea-bird with an astoundingly large wingspan - who could easily guide them to shore; hence the 'light in the darkness' vibe. (For anyone wondering, in the poem the Captain shoots the bird down and the crew perish... Can't quite remember why).
It also merges the bird/ocean thing already going on...
It was just a though