Members of this phylum range in size from a single-celled organism to around 2-3 feet long.

Classification of Flatworms

The Platyhelminthes classification is given below:

• • Turbellaria

These are free-living organisms found primarily in fresh water.

The body is dorsoventrally flattened, hooks and suckers are not present. For example,  Planaria, Otoplana.

• Trematoda

These are mostly parasites. Hooks and suction cups are usually present. For example,  Fasciola hepatica, Diplozoon.

• Cestoda

These are exclusively parasites. They have hooks and suction cups. For example,  Taenia spp., Convoluta.

Some organisms that belong to these species cause serious illnesses, such as schistosomiasis or snail fever. It is one of the most dangerous diseases in tropical countries. Tapeworm is another disease caused by tapeworms.

Examples of flatworms

1. Dugesia (Planaria)

These are found in freshwater ponds or slow currents. Its body has cilia and it has the power to regenerate the lost part. The head has one pair of eyes and two side lobes.

1. Schistosoma

It is found in the mesenteric blood vessels and in the hepatic portal system of humans and is therefore known as the blood fluke. It shows well marked sexual dimorphism .

The schistosome causes schistosomiasis, which is spread through contaminated water. The patient suffers from anemia, pain, fever, enlarged liver and spleen, and diarrhea.

1. Fasciola

It is also known as liver fluke as it resides in the liver and bile duct of sheep and goats. It is a hermaphrodite, but cross fertilization takes place.

Causes fascioliasis in animals. In this, the liver of the animal is enlarged and the bile ducts are blocked. The infection weakens the muscles of the animals and causes muscle pain. It could also be fatal to animals.

1. Taenia solium

It is also known as the pork tapeworm and is found in all countries where pork is consumed. They live as parasites in the small intestine of humans and their larvae are found in the muscles of pigs. It is a hermaphrodite and is self-fertilizing.

Taenia solium causes taeniasis, where the patient experiences abdominal pain, anemia, indigestion, restlessness, and a false appetite.

1. Taenia saginata

There are other organisms like  Taenia saginata  that is transferred through beef in the human intestine and  Echinococcus granulosus  that lives in the intestines of cats and dogs.

1. Dipylidium caninum

It is the typical parasite of cats, dogs and other animals that host fleas.

1. Hymenolepis nana

This cestode affects rodents and people, causing hymenolepiasis. It causes weight loss, severe diarrhea, malnutrition, dehydration and severe abdominal pain.

Characteristics of flatworms

• • They are triploblastic, acoelomated, and bilaterally symmetrical.
  • They can be free-living or parasites.
  • The body has a smooth covering with or without cilia.
  • Its body is dorsoventrally flattened, without any segment and appears as a leaf.
  • They are devoid of the anus and the circulatory system, but have a mouth.
  • They breathe by simple diffusion through the surface of the body.
  • They have a level of organization of the organ system.
  • They do not have a digestive tract.
  • The space between the body wall and the organs is filled with connective tissue parenchyma that helps transport food material.
  • They are hermaphrodites, that is, the male and female organs are present in the same body.
  • They reproduce sexually by fusion of gametes and asexually by regeneration, fission and regeneration . Fertilization is internal.
  • The life cycle is complicated with one or more larval stages.
  • They possess the quality of feedback.
  • Flame cells assist in excretion and osmoregulation.
  • The nervous system comprises the brain and two longitudinal nerve cords arranged in a ladder pattern.

Unique Characteristics of Flatworms

Some of the characteristics that distinguish organisms belonging to the phylum Platyhelminthes (flatworms) from others are:

• Presence of flame cells
• Stairway nervous system
• Presence of parenchyma in the body cavity
• Own fertilization