Phylum- Platyhelminthes

Phylum- Platyhelminthes

Phylum Platyhelminthes includes 13000 species. These are found as free-living as well as parasitic life forms. These are also called Flatworms because of having a dorso-ventrally flattened body.

Characteristics features of Phylum- Platyhelminthes

• They may be found as free-living or parasite
• These are mostly endoparasites, found in various animals including human beings.
• Symmetry: These are Bilaterally symmetrical.
• Germinal layer: triploblastic animals.
  • Triploblastic– In a developing embryo, the third germinal layer called mesoderm is found in between ectoderm and endoderm. These animals are called triploblastic animals
• The body cavity: Acoelomate animals
• Level of organization: organ level of organization is found.
• In parasites the hooks and suckers are present.
• Some parasitic organisms absorb nutrients directly from the host body’s surface.
• Flame cells: these are specialized in this phylum which helps in osmoregulation and excretion. Chief excretory waste is ammonia.
• Hermaphrodites ( bisexual or monoecious) Sexes are not separate, internal fertilization.
• The development occurs through many larval stages.
• Some members of this phylum possess a high regeneration capacity. e.g., in Planaria.
• Some examples of Platyhelminthes: Taenia solium (tapeworm), Fasciola hepatica (Liver fluke)

Examples of Platyhelminthes

Classification of Platyhelminthes:

The Platyhelminthes can be divided as:

1. Turbellaria
2. Trematoda
3. Cestoda

Turbellaria :

Characteristic features of Tuberllaria:

• These are mostly found in fresh-water
• These animals are free-living
• Hooks and suckers are absent
• Example; Planaria, Otoplana

Trematoda

Characteristic features of Trematoda:

• The animals are mostly parasitic
• Presence of Hooks and suckers
• Example: Fasciola hepatica, Diplozoon

Cestoda

Characteristic features of Cestoda:

• The members are the exclusively parasitic
• presence of hooks and suckers
• Example: Taenia sps. Convoluta

Some Examples of Platyhelminthes:

Planaria: Found in freshwater. The Body comprises cilia and has the power to regenerate the lost part. They possess a pair of eyes and two lateral lobes.

Schistosoma: These are called blood fluke because found in mesenteric blood vessels and the hepatic portal system of humans. It shows well-marked sexual dimorphism.

• They spread many diseases by contaminating the water.

Taenia solium: also called pork tapeworm and found in all countries where the consumption of pork occurs. The larva of this organism is found in the pig’s muscles. Taenia solium lives as a parasite in the intestine of the human. It is a hermaphrodite organism and it undergoes self – fertilization.

Fasciola: Also called the liver fluke, it lives in the bile duct of sheep and goats. It is also hermaphrodite but in these organisms cross-fertilization takes place.

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• Phylum Ctenophora

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