Sources : Sea-horse

Isidore of Seville [7th century CE] (Etymologies, Book 12, 6:9): Sea-horses [equus marinus] are so called because they are horses [equus] in their front part and then turn into fish. - [Barney, Lewis, et. al. translation]

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Marine monsters 6.18, 6.57): [Thomas describes the sea-horse under the names equus maris and zydrach.] [Marine monsters 6.18] The sea horse (equus maris) is a large monster. This monster is the strongest of almost all marine monsters. Nothing can do without water, as Aristotle says; but as soon as nature lacks water, it will also lack life. But the latter part [tail] of the sea-horse ends in the nature of a fish. It lives on the flesh of other fish. In battle it is cruel, but it fears man, and fears that wars will be fought against it. [Marine monsters 6.57] Zydrach is a sea monster of a very strange form, and which pretends malice in its appearance, but is nevertheless harmless. It has a head shaped like a horse's, though of a smaller form; but the body is very similar to the dragon in every respect. It has a tail long in proportion to the size of the body, slender and tortuous like a snake. The whole body has different colors. Instead of wings it has fins like a fish, and it moves from place to place by swimming. - [Badke translation/paraphrase]