This is one of many pictures of a moscaic on the subject of Oceanous and Thetys. From Enc. Britt.: In Hesiod's Theogony, Oceanus was the son of Uranus (Heaven) and Gaea (Earth), the husband of the Titan Tethys, and father of 3,000 stream spirits and 3,000 ocean nymphs. In Homer's works he was the origin of the gods. As a common noun the word received almost the modern sense of ocean. Hence in details all sorts of "sea life" appear.