A body cavity without a coelom. Have only one internal space, the digestive cavity. Has a gut cavity, lined with endoderm-derived cells, and surrounded by a mass of tissue derived from the mesoderm. Mesoderm turns to Parenchyma.
When a plan passes through a sagital plane and there are two equal halfs.
non-cilliated body covering that is designed to tegument. Can resist the immune system and digestive juices.
Free-living flatworms.. Are bottome dwellers in marine or freshwater environments. Is dipicted as a paraphyletic taxon.