Adella is the third daughter of King Triton and Queen Athena. She has a chartreuse yellow tail and wears a chartreuse green seashell bra. Her dark brown hair is tied in a ponytail with a pearly hairband and headpiece that both match the color of her tail. Her appearance varies slightly in the TV series, where she wears a gray hairband and animated to be somewhat heavier than her sisters. However in the prequel films and coloring pages, she has the exact same figure as her sisters. In the original film, she has a more realistic heavy figure compared to the childish one in the TV series, but wider than the prequel. The prequel establishes that she is boy-crazy, often dreaming about and flirting with them. In the books, she tends to be shallow and vain and she has many dates with merboys.
Adella appears at the beginning of the film, where she is performing the song "Daughters of Triton" alongside her other sisters. Afterwards, she only has cameo appearances alongside them.
Most of Adella's appearances are cameos alongside her other sisters. She is obviously chubby when sketched for the series. In the episode "Trident True", she is the victim of a practical joke courtesy of Urchin. When she tries to comb her hair, she ends up having a bad hair day. At the end of the episode, she presents Triton with a father's day present, and it is implied that she gives him the same thing every year.
Adella makes a small cameo appearance at the beginning of the film. She attends the christening of her niece, Melody, and is seen in a group shot with her other sisters.
Adella first appearance in the film is as a young girl. She is relaxing in a cove alongside her sisters and parents, but is forced to flee when pirates attack. Her mother, Athena, is killed in the attack, which devastates the family. As a result of his grief, Triton bans music (Athena was a noted lover of it), and has Adella and her sisters be strictly raised by their governess, Marina Del Rey.
As a teenager, Adella learns from Ariel about a secret underground club called The Catfish Club. She secretly attends alongside of them and start dancing with a fat male sea slug, but is caught by Marina and punished by Triton. At the end of the film, after music is restored to Atlantica, she is seen kissing a merboy.
- Her name is a feminine form of "Adam".
- Shea is a renaissance era name.
- In Little Mermaid 2, there are actually two versions of her. One version has a hefty Adella, drawn similarly to how she was in the TV series, but at a later time, that model was scrapped to resemble the one in the third film.
- She explicitly states that she is two years older than Ariel, making her 17 in the third film and 18 in the first. It could be that her birthday is before Ariel's, so when she turns 18, Ariel will still be 15.
- She is obssessed with boys; hoping to find the perfect one.
- In the first film, she was the heftiest of them all, and since then her size has varied. During the TV series, her weight was exaggerated to make her quite chubby. Since then however, her body was greatly reduced to resemble Ariel's.
- Her voice actor is also the same of that of her niece, Melody.