Vintage swimsuits by Cole of California have wonderful details and design. This set from 1952 is featured as "Heavenly Bodies". Both show lines of elastic shirring in the back panel (which probably has a center zipper as well). The front is probably darted, lined and has boning to create the corset shaping. The bright print with cuffed sweet heart edge are classic to the era. From the ad details:
Swimsuits designed to make any "body" more heavenly. One conceals, one reveals.
Left, the slim-skirted wonder of the year. Wraps around to adjust to almost any figure and sleek away inches.
Right, molded version to dreamline your curves.
In vibrant fine cottons, elasticized with Matletex.
Each $12.95 at fine stores.
Here's a closer view to show off that great look. The strapless fitted style has a sheath front for modesty, and there is shirring across the 'tummy' area. The wrap skirt style has a similar bodice but probably has shorts under that skirt.