Talassia has very long blond hair and brown eyes, made up of sky blue. Some strands of her hair are adorned with orange pearls. Her bra is very long and looks more like a tunic, sky blue, marked by cutouts on the side and a shell in spiral gilded as a brooch. She has pink ruffles on her arms and a long sky-blue mermaid tail adorned with pink ruffles.
Talassia is a very gentle and sweet mermaid. She is very innocent and shy. She is also shown to be timid.
Talassia is captured by Valtor's evil spell, along with Coralia and Amarea. Valtor places his mark on them; stealing their magic and changing them into sea monsters that attacked anything that crossed their paths. After Valtor's defeat, Talassia's magic returned, she became a normal mermaid again and she returns home to the Underwater Kingdom.
Talassia appears again in "The Enchanted Island". The guardian of Tir Nan Og took the form of three mermaids from Andros; Talassia, Coralia, and Nerimer. Talassia lures Aisha out into the water. After Aisha introduces herself, fake mermaids pushes Aisha underwater and with their fight against the Winx in a dungeon.
- "Talassia" is a genus of very small sea snails.