Due to a printing error when being manufactured, the 1989 Disney character’s famous shell bra had not been printed.
The student made the discovery on the rails at the supermarket at Ventura Park in Tamworth, Staffordshire, on Tuesday 20 June.
“I couldn’t believe my eyes,” she said. “I thought ‘that isn’t right’.”
Mosson had been shopping with boyfriend Daniel Bayliff, 22, for clothes for their holiday to Greece.
She said the Asda George swimsuit was for children aged three to four and on sale for £7.
Mosson said: “To see Ariel without her trademark shell bra has scarred me for life and ruined a childhood classic.
“She’s a much-loved Disney character from a children’s film. She should definitely not be in the buff, that’s for sure.
“I grew up watching this film and it’s certainly not how I remember her looking. It’s outrageous.”
Mosson added: “How on earth nobody has spotted that is beyond me. It should not have slipped through quality control and then shop floor staff should have noticed it too.
“It was right on the front of the rail - anybody could see it. Its disgusting really, a child could get really confused by that.
“We both said if the design was to have a bikini top sewed onto it, it should have had a bikini top printed on too just incase something like this happened.
“They need to remove it from the shelves immediately.”
Mosson contacted Asda on Twitter to ask for an explanation.
She wrote: “Absolutely mortified to see this on Asda’s shelf this evening @asda
A 3-4-year-old swimming costume. What’s going on?”
Mosson said: “They just replied and said it was a printing error on the costume and the manager had been informed.
“But it makes you think whether any others could have slipped through the net.
“It might be the idea of some people’s weird fantasy - but it should definitely not be on display in a supermarket and sold for children to wear.
“Imagine if you spotted a kid wearing that on your summer holidays, you’d be absolutely mortified.”
An Asda spokesperson said: “We’re sorry for the printing error on ‘The Little Mermaid’ swimsuit, which was caused during the production process.
“It only affected a very small number of the swimsuits, which were available from George, but we’d like to reassure our customers that we have removed all stock from sale and will ensure this doesn’t happen again.”