The platyhelminthes phylum have different types of species found inside of the phylum. It has three different classes Turbellaria which includes free living flat worms. They usually live in fresh water or saltwater they are very versatile. The second is Trematoda which are flukes, external and internal parasites. Lastly is the Cestoda which are tapeworms the adults of parasites these can be potentially deadly to humans. These species have different characteristics which include being symmetrically bilateral. They have no body and are usually flattened, no true segmentation. Their epidermis is soft and ciliated and covered with cuticles. They have external suckers or hooks for connection to their hosts (parasites). The digestive system is incomplete with a mouth but no anus and usually branched. The muscles are very well developed and they have no skeletal or circulatory systems. The Nervous system is a pair of anterior ganglia, or a nerve ring connected to pairs of longitudinal nerve chords.
Distinct tissues and organ systems are found, but the organs are not located in a body structure. Experiments of these animals show that, except for the digestive cavity, no other internal cavity is found. Because the organs are in direct contact with a surrounding loosely organized tissue, these animals lack a coelon, or a skeleton structure. These animals have three layers of cells can be seen: an outer epidermis (ectoderm), a middle layer that may be several cells thick and a lining of the gut the endoderm which is one of the primary germ cells layers. The digestive system is described as incomplete because it is not a tube with a mouth at one end and anus at the other. There is only one opening, so it is described as a sac like system. Food enters the mouth and is digested in a gastrovascular cavity which distributes food and precious materials to all other parts of the body. Any non-digestable food must be vomited back through the mouth. In trematodes, the digestive system is usually a blind sac. A mouth is usually found near the anterior end and a muscle is usually behind the mouth and is used to suck in food. The gut can be saclike or highly branched, but an anus is usually absent. Wastes are eliminated through the mouth. No digestive system is found in cestodes.
The tapeworms are highly adapted to life as internal parasites usually living in the gut of the host animal or humans. The larger tapeworms are found in the gut of mammals, and smaller types of fish. Tapeworms can reach a length of more than 30 meters, establishing them amongst the longest known invertebrates. They have no mouth or digestive system. Nutrients from the host digestive system are absorbed directly through the outer cuticle which is thickened and without cilia.
The head is usually packed with hooks or suckers which fasten to the host gut wall and provide an anchor to prevent removal of the worm. The body is divided into sections called proglottids containing little more than reproductive organs.
The head is usually packed with hooks or suckers which fasten to the host gut wall and provide an anchor to prevent removal of the worm. The body is divided into sections called proglottids containing little more than reproductive organs.