Sources : Sea-mouse

Pliny the Elder [1st century CE] (Natural History, Book 9, 76; 9, 88; 11, 62): [Book 9, 76] The sea-mouse digs a trench in the ground to lay its eggs in and covers it again with earth, and a month later digs the earth up again and opens the trench and leads its brood into the water. [Book 9, 88] But on the other hand instances of friendship, in addition to the creatures whose alliance we have mentioned, are the whale and the sea-mouse: because the whale's eyes are over-burdened with the excessively heavy weight of its brows the sea-mouse swims in front of it and points out the shallows dangerous to its bulky size, so acting as a substitute for eyes. [Book 11, 62] The sea-mouse that swims in front of the whale has no teeth, but instead of them its mouth inside and also its tongue and palate are set with bristles. - [Rackham translation]

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Fish 7.57): The sea-mouse [mus marinus] comes out onto the land and makes a trench in the earth, lays eggs and collapses the earth on them; but returning after the thirtieth day, it opens the ditch again and leads its offspring into the water. Its offspring are blind at first, as are in general the offspring of all aquatic animals. - [Badke translation/paraphrase]