Flatworms (phylum Platyhelminthes) may be more frequently mistaken for sea slugs than any other animals. Some of them are brilliantly colored and many have folds of the body margin or small projections from the dorsal surface that resemble rhinophores. A few even have elongate papillae on the dorsal surface that may be mistaken for cerata. However, they are usually proportionately flatter and move more rapidly than sea slugs (either by ciliary action or undulation). They lack the molluscan foot and an anus. All or nearly all are predators and some of the larger species may feed on sea slugs. Others mimic sea slugs that concentrate toxic or distasteful chemicals from their food. Most of those that are readily mistaken for sea slugs are in the order Polycladida. A few of the species most frequently mistaken for sea slugs:

Pseudoceros cf. dimidiatus PF; La Perouse Bay, Maui	Pseudobiceros gratus CP: Hekili Point, Maui; March 30, 2007	Pseudoceros ferrugineus PF: Makena, Maui; Sept. 20, 2008
Pseudobiceros sp. #5 CP: Maui; May, 2005	Pseudobiceros sp. #14 CP: Hekili Point, Maui; March 23, 2007	Thysanozoon tentaculum CP: Maalaea Bay, Maui; Oct. 22, 2007

For more information see:   John Hoover's flatworm page   Keoki Stender's flatworm page   Marshall Islands Flatworms by Scott & Jeanette Johnson   Jim Anderson's flatworm pages   Gustav Paulay's Guam flatworms   Flatworms on the Sea Slug Forum   Discover Life flatworm pages by Marian K. Litvaitis   Flatworms at Umiushi-zukan   Reunion Flat Worms by Philibert Bidgrain   Guam Flat Worms by Dave Burdick   Flatworms by Teresa Zubi   Australian flatworms by Denis Riek Marine Flatworms Facebook Group