Platyhelminthes
Platyhelminthes are a Phylum of worms usually referred to as flatworms.The are usually found in aquatic habitats but some species have been known to live in moist areas on land. They have soft bodies and three germ layers. The muscle layers are well developed and it does not have a body cavity. There is no true segmentation like its relatives, but lacks a vertebrate like all of them. It's epidermis is soft and covered with a cuticle with suckers and or hooks for connection for its host. It also has an incomplete digestive system. It has a mouth but lacks an anus. It also lacks skeletal, circulatory, and respiratory systems. It's nervous system is a pair of anterior ganglia or a nerve ring connected to 1 to 3 pairs of long nerve chords.
The Divided Flat Worm
The Divided Flat Worm is a flat worm that belongs to the Platyhelminthes Phylum and the Turbellaria Class. It can be found in the coral reefs of the Indian Ocean or the Western Pacific Ocean. They have no cuticle. In a few species, the skin is a syncitium which is a collection of cells with multiple nuclei and a single, shared, external membrane. However, the skin of most Flat worms consists of a single layer of cells. They have many glands submerged in their muscular layers below the skin and they connect to the surface by pores through which they secrete mucus, adhesives, and other substances. The divided flat worm have a simple pharynx lined with cilla feed by sweeping food into their mouths located on their underside.
Monogenea
Monogenea are very small parasitic flatworms mainly found on skin or gills of fish. They are part of the Platyhelminthes Phylum. Monogeneans lack respiratory, skeletal and circulatory systems and have no or weakly developed oral suckers. Monogenea attach to hosts using hooks, clamps and a variety of other structures.Like other flatworms, Monogenea have no body cavity. They have a simple digestive system with a mouth opening with a muscular pharynx and an intestine with no end opening. They posses three embryonic germ layers: endoderm, mesoderm, and ectoderm. In addition, they have a head region that contains concentrated sense organs and nervous tissue.
Trematoda
Trematoda or commonly referred to as flukes, are parasitic flatworm. They are part of the Platyhelminthes Phylum. Nearly all flukes are parasites of mollusks and vertebrates. They do not contain any respiratory organs. Their most distinctive external feature is two sucker, one close to it's mouth and the other on it's underside. It's brain has a pair of ganglia in the head region, from which two or three nerve chords run the entire length of it's body. They also generally lack any sense organs.The mouth is located at the forward end of the animal, and opens into a muscular pharynx. The Pharynx connects via a short esophagus. Most trematodes are simultaneous hermaphrodites, having both male and female sex organs.