This has allusion to one of the myths in Bullfinch’s Mythology, a small part which reads as follows:
In the sea that washes the coast of Ireland there is an island called Ebuda, whose inhabitants, once numerous, had been wasted by the anger of Proteus till there were now but few left. This deity was incensed by some neglect of the usual honors which he had in old times received from the inhabitants of the land, and, to execute his vengeance, had sent a horrid sea-monster, called an Orc, to devour them. Such were the terrors of his ravages that the whole people of the isle had shut themselves up in the principal town, and relied on their walls alone to protect them.
[…]
The horrible monster was like nothing that nature produces. It was but one mass of tossing and twisting body, with nothing of the animal but head, eyes, and mouth, the last furnished with tusks like those of the wild boar.