Amphitrite

Amfetriti was a Mermaid and the daughter of Nereus. She herself had a daughter called Galliteya.

Biography
Amfetriti was found by De Requin when she and her daughter became trapped in a fishing net. He took her aboard the Lankester in hopes of selling her. Amfetriti adopted the name "Amy Ivans". To disguise her tail, Amy sat in a wheelchair and claimed she was paralysed. Amy fell ill and so was resigned to her cabin. The Sixth Doctor and Peri Brown were assigned to treat her.

Amy was given small doses of mercury by De Requin. De Requin tried to force feed Peri mercury but she resisted and in the following fight, Amy's chair was knocked over, revealing her true form.

Amy revealed to Peri her name and showed her where De Requin kept Galliteya. She then died of suffication from being out of the water in her wheelchair. (BFA: Cryptobiosis)