Comparison to other phyla

- They have a more developed organ systems than either sponges or cnidarians.

- The flatworms are:

- Soft bodied

- Have a solid body form

- Are hermaphroditic

- Have spermatozoa with 2 tails

- Have a sack like gut

- Have epidermal cells that are multiciliated

- Have fiber form muscles

- And have neoblasts

Thus they stand distinct from all other major phylum of worms, the Annelida, whose members have a complete gut, segmented bodies with fluid- filled coelomic compartments, a cuticle- covered body wall, muscles that arise from epithelial mesodermal tissue, and monoflagellated sperm. Hermaphroditism, with reproductive organs as complicated as those of the flatworms, appear in the Gnathostomulida and Gastrotricha. The multiciliated epidermal cells (all worm phyla but the Gnathostomulida), the solid (acoelomate) bodies (Gastrotricha and miscellaneous representatives of Nematoda, Annelida, etc.), and fiber-form muscle cells.