Pliny the Elder [1st century CE] (Natural History, Book 9, 17; 32, 9; 32, 19): [Book 9, 17] A fish very like a sea-pig is drawn out with teams of oxen, especially in the river Main in Germany, and in the Danube with weeding-hooks; an exceptionally large species with no internal framework of bones or vertebrae and very sweet flesh is recorded in the Dnieper. [Book 32, 9] Apion tells us that the largest a of the fishes is the pig-fish, which the Lacedaemonians call orthagoriscus, saying that it grunts when it is caught. [Book 32, 19] Among poisonous parts of fishes are the prickles on the back of the sea-pig, a wound from which causes severe torture. A remedy is the slime from the liquid part of the body of these fishes. - [Rackham translation]

Isidore of Seville [7th century CE] (Etymologies, Book 12, 6:12): Sea-pigs [porcus marinus], commonly called suilli [“small swine”], are so named because when they seek food they root up the earth underwater like swine. At their throat they have what functions as a mouth, and unless they submerge their snout into the sand, they do not collect food. - [Barney, Lewis, et. al. translation]

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Fish 7.66): The sea-pig [porcus marinus] is a delicate fish. The species of the land pig is kept in many regions. Indeed, the sea-pig has a very similar head, and the limbs in the body and the ribs are arranged in the manner of a pig. Almost all of its flesh is turned into thick fat. Its tongue is absolutely like that of a pig, but its voice is different. On its back there are certain spines having a very effective poison; but the remedy for their effect is the points of those thorns. And the torment from the poison is great. As Pliny writes, they look for food at the bottom of the sea and dig it up after the manner of pigs. They have an opening around the throat. - [Badke translation/paraphrase]

Bartholomaeus Anglicus [13th century CE] (Liber de proprietatibus rerum, Book13.26): And he sayth of the sea swine, that is commonly called Suyllus, that while hée seeketh his meat he froteth under water in the ground, as it were a swine: and hath a manner mouth about the throat, and gathereth no meate but he pitcheth ye snowte in gravell. - [Batman]