Neptune, the god of the sea, is depicted nude next to his scantily-clad wife, Amphitrite. Neptune is easily recognizable by the trident that he’s holding in his left hand. Already in the Theogony, the epic poem about the origins of the world and the gods, attributed to Hesiod (fl. ca. 700 BC), he and Amphitrite are a couple (ll. 930-933).
Amphitrite was the daughter of Nereus, a child of the primordial deities Pontus (Sea) and Gaea (Earth). Nereus had many daughters, who are all referred to as Nereids as a result (literally, the offspring of Nereus). In his Bibliotheca, Apollodorus refers to Amphitrite as an Oceanid, i.e. a daughter of the god Oceanus (from whom we derive our word “ocean”).
According to the Astronomica, a book that deals with the myths associated with the constellations and written by the Roman author Gaius Julius Hyginus (ca. 64 BC-AD 17), Neptune had fallen in love with Amphitrite, but she fled from him and sought refuge with Atlas. Among those the god of the sea sent out to look for her was Delphinus (the Dolphin), who managed to find her. In gratitude, Neptune turned Delphinus into the constellation Dolphin.
It’s not the most romantic story, but then again Classical mythology isn’t exactly known for its romanticism. We can hope that the owner’s marriage came about under happier circumstances (even though most marriages in ancient times were arranged). More likely, Neptune refers to the owner’s connections with the sea; he may have been a merchant or otherwise earned his wealth through seaborne trade.