slidor, adj: slippery. (“slee-dohr”)
I’m guessing these sea-pigs are slidor. Porci marini dig up the ground under water like pigs do on land. They must submerge their snout in the sand in order to gather food. From The Medieval Bestiary. Kongelige Bibliotek, Gl. kgl. S. 1633 4, fol. 61r.