Platydoris carolynae is a large, flattened leathery nudibranch with a distinctive pattern of irregular, merging black or brown markings on a cream background. The underside of the mantle is also cream with black or brown spotting, each spot made up of multiple fine cross-hatched lines. The rhinophores are tan-coloured with dark brown spots. Gills are translucent with dark brown or black specks.
Can be found in shallow water, subtidal, tide pools and shallow subtidal, associated with sponges.