Animal Kingdom

Phylum Platyhelminthes


Did you know, potentially life-endangering parasites can live in the human body for up to several decades? Moreover, these parasites, known as blood flukes, have the ability to regenerate themselves. And so, can survive in hostile environments. Furthermore, these worms belong to Phylum Platyhelminthes. Let us explore this phylum.

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Phylum Platyhelminthes

Platyhelminthes - Bedfords Flatworm

(Source: Wikipedia)

Platyhelminthes are commonly known as flatworms or tapeworms. They are a group of soft-bodied invertebrate animals. As a matter of fact, there are around 20,000 species of these animals. A few of these live as parasites on humans and other animals. Furthermore, it is because of this parasitic nature that they do cause some amount of trouble for the host animal. A few species belonging to this phylum can be a major cause of certain diseases. For example, Schistosomiasis, or bilharzia or bilharziasis, is a disease caused by these parasitic flatworms. They belong to the family Schistosomatidae.

The most distinguishing feature of these invertebrates is their flat body. As the body does not have any cavity, they are flat. The body is also not segmented and they do not have specialized systems. Around eighty percent of the flatworms are parasitic in nature, while a few free-form flatworms are also present. The free-living forms are scavengers or predators. The parasitic species feed on the tissues of the host organism in which they live.

The animals in this phylum have a diverse range in size. Some are microscopic, while a few go up to two feet long. They are also hermaphrodites, which mean that both the sexes are present in the same organism.

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Characteristic features of Phylum Platyhelminthes

Planaria Nervous system

(Source: Britannica)

  • Their body is dorsoventrally flattened.
  • They exhibit bilateral symmetry.
  • Also, they are triploblastic, with three germ layers.
  • They do not have a body cavity and are acoelomate.
  • The body is soft and unsegmented.
  • They are mostly parasitic with a few free-living
  • They exhibit an organ system grade of organization.
  • The digestive system is incomplete or absent. In fact, there is a single opening which leads to a well-developed gastro-vascular cavity. Also, the anus is absent. And there is no true stomach structure. In a few species, the digestive system is completely absent.
  • Respiratory and circulatory systems are absent. In fact, the respiration generally occurs by simple diffusion through the body surface.
  • The flame cells help in excretion. The excretory system has protonephridia with the flame.
  • A primitive nervous system is present.
  • These animals are hermaphrodites i.e. both male and female organs are present in the same body
  • Sexual reproduction happens through gametic fusion.
  • Asexual reproduction also happens in a few species through regeneration and fission.
  • Fertilization is internal.
  • The life cycle of these organisms can be complex, especially if they are parasitic, as this may involve one or more host animals.

Learn more about Phylum Mollusca here.

Classification of Phylum Platyhelminthes

The different classes under this phylum are:

  • Turbellaria
  • Trematoda
  • Cestoda

Platyhelminthes Examples

  • Taenia (Tapeworms)
  • Fasciola (Liver fluke)
  • Taenia saginata (Beef tapeworm)
  • Echinococcus granulosus – The dog tapeworm
  • Planeria (freshwater flatworm)
  • Opistorchis

Learn more about Phylum Hemichordata here.

Solved Questions for You

Q: Which is the phylum, where the body is dorsoventrally flat without a body cavity?

Ans: Phylum Platyhelminthes.

Q: Give an example of a free-living

Ans: Planaria

Q: The digestive system is absent in which class of flatworms?

Ans: Class Cestoda.

Q: Phylum Platyhelminthes shows which grade of organization?

Ans: It is the first phylum to show organ system grade of organization along with bilateral symmetry.

FAQ’s for You

Q1.In phylum Platyhelminthes, the excretory organs are?

Answer: A flame cell is a specialized excretory cell found in flatworms (except the turbellarian order Acoela), rotifers and nemerteans. Flame cells function like a kidney, removing waste materials.
The nephridium is an invertebrate organ that occurs in pairs and performs a function similar to the vertebrate kidney. Nephridia remove metabolic wastes from an animal’s body.
The malpighian tubule is a tubular excretory organ, numbers of which open into the gut in insects and some other arthropods.
Green glands are excretory organs in Crustaceans.

Q2. Members of phylum platyhelminthes are generally called as?

Answers: Platyhelminthes very commonly known as flatworms or tapeworms, these animals are soft-bodied invertebrate animals. There are around 20,000 species of these animals. A few of these live as parasites on humans and other animals.

Q3. Mention the unique features of phylum platyhelminthes.

Answers: The unique features of the phylum Platyhelminthes are as follows:
They have a dorso-ventrally flattened body
The body is covered with the ciliated epithelium
These are acoelomate
They have a sac-like digestive cavity
They possess a great regeneration power.
These are mostly parasitic.
Excretion occurs by means of flame cells.
Examples include Planaria, Taenia etc.

Q4. Mode of nutrition in platyhelminthes is?

Answer: Phylum Platyhelminthes includes triploblastic, acoelomate, bilaterally symmetrical and dorsoventrally compressed flatworms. Phylum Platyhelminthes has following characteristic features:
(1) Free-living, commensal or parasitic forms. They are heterotrophic in nature.
(2) Body cavity (coelom) lacking.
(3) Soft-bodied, unsegmented worms.

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