Phylum Platyhelminthes

Phylum Platyhelminthes

(Greek; platys= Flat; helmins = worms); The flatworms.

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

The Platyhelminthes are mostly parasitic and live on or inside the host. A few are free-living and aquatic. The body of flatworms is thin, soft, unsegmented, and dorsoventrally flattened. They may be leaf-like or ribbon-like animals.

• 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: The 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.
• Hermaphrodites ( bisexual or monoecious) Sexes are not separate, internal fertilization.

Special Characters:

Flame cells:

Flame cells are the specialized in this phylum which helps in osmoregulation and excretion. Chief excretory waste is ammonia in Platyhelminthes.

Power of regeneration:

Some members of this phylum possess a high regeneration capacity. e.g., in Planaria.

Larval statges in Platyhelmithes

• The development in Platyhelminthes occurs through many larval stages. for example, the life cycle of fasciola includes miracidium larva, sporocyst larva, redia larva, cercaria larva, and metacercaria larva.
• The larval forms of Taenia are hexacanth larva and cysticercus larva.

Examples of Platyhelminthes:

Parasites: Fasciola hepatica (Liver fluke), Taenia (Tapeworm), Schistosoma (Blood fluke)

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 – 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.

Schistosomes: These are called blood flukes 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.

Free-living: Planaria

planaria- It is 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.

Examples of Platyhelminthes

Classification of Phylum Platyhelminthes:

The Platyhelminthes can be divided into:

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
• For 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

You can also read: 💡

• Diseases 
• Pathogenic diseases
• Phylum Porifera
• Phylum Coelenterata
• Phylum Ctenophora

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