Thetis is a figure from Greek mythology with varying mythological roles. She mainly appears as a sea nymph, a goddess of water, and one of the 50 Nereids, daughters of the ancient sea god Nereus.
Statue of Thetis with a triton, Roman copy
Immortal Thetis with the mortal Peleus in the foreground, Boeotian black-figure dish, c. 500–475 BC - Louvre
Thetis changing into a lioness as she is attacked by Peleus, Attic red-figured kylix by Douris, c. 490 BC from Vulci, Etruria - Bibliothèque nationale de France in Paris
Thetis dips Achilles in the Styx by Peter Paul Rubens (between 1630 and 1635)
In Greek mythology, the Nereids or Nereides are sea nymphs, the 50 daughters of the 'Old Man of the Sea' Nereus and the Oceanid Doris, sisters to their brother Nerites. They often accompany Poseidon, the god of the sea, and can be friendly and helpful to sailors.
Nereid half reclining on the back of a hippocampus, fresco from Pompeii
French Empire mantel clock (1822) depicting the nereid Galatea velificans
Nereid riding a sea-bull (latter 2nd century BC)
The Nereid Monument. From Xanthos (Lycia), modern-day Antalya Province, Turkey. 390–380 BC. Room 17, the British Museum, London