Thank you for viewing. This is a 9M size solid color short swimsuit (black) from Riberce, purchased last month. It can also be used as yoga wear. You don't need to wear another swimsuit underneath; this one is fine on its own. I only tried it on and will not be using it, so I am selling it. Since it has never been used, it is in new condition. Please feel free to ask if you have any questions!