Biology

Phylum Platyhelminthes Examples and Characteristics

(Triploblastic Animals - The Acoelomates)

Platyhelminthes Examples

The common examples of flatworms are:

  • Dugesia (planaria): It is a free-living flatworm. It has a ciliated outer surface.
  • Fasciola (liver fluke): It is an endoparasite in sheep and sometimes, in man. It lives in the bile duct of its host. Platyhelminthes have a sucker for attachment to host tissues. It completes its life cycle in two hosts, snail, sheep, or man.
  • Taenia (tapeworm): It is an endoparasite of humans, cattle, and pigs. It completes the 1ts life cycle in two hosts. The intermediate host is pigs or cattle.

Their body is ribbon-like and it is divided into segments called proglottids. These segments contain many sex organs. The segments continuously break from the body and pass out from the intestine of the host with feces.

General Characters of Platyhelminthes

  1. The name Platyhelminthes means “flatworm”. Their body is soft and dorso-ventrally compressed.
  2. They are acoelomate i.e. body cavity or coelom is absent in them.
  3. Their body is composed of three layers. They develop a third layer between ectoderm and endoderm. It is called the mesoderm.
  4. They show bilateral symmetry and the body is unsegmented.
  5. Most of the Platyhelminthes are parasites. Mostly, they are endoparasites, i.e. live inside their hosts. These parasites are more common in the tropics. The most common examples are:
  • Taenia solium (tape worm)
  • Fasciola hepatica (liver fluke)
  • Schistosoma (blood fluke)

A few species are free living. They live in freshwater, for example, Dugesia (planaria).

  1. Their size may be from a few millimeters (10mm in case of planaria) to several meters (tapeworm).
  2. They have a branching sac-like digestive system. It occupies most of the space of the body. The digestive system is poorly developed in parasites. It may be absent in tape-worms. The parasite species absorb nutrients from the hosts. Free-living species like planaria feed on small animals and bodies of dead and decaying animals.
  3. The excretory system consists of branching tubes. The tubes end in bulb-like cells called flame cells.
  4. A well-developed nervous system is present in Platyhelminthes. It is in the form of a simple network of nerves or ganglia. The sense organs are present at the anterior end.
  5. Respiratory and circulatory systems are absent.
  6. The free-living forms like planaria are motile (can move). They move by cilia. The cilia are present under their surface. The parasitic forms show limited movement.
  7. They reproduce both sexually and asexually.
  • Asexual reproduction: It takes place by binary fission. In this case, the animal constricts in the middle and divides into two pieces. Each of these regenerates the missing part.
  • Sexual reproduction: The sexually reproducing species is hermaphrodite. In this case, both male and female reproductive organs are present in the same animals. In some cases, larvae are also developed.

Adaptation for Parasitic Mode of Life

The parasitic Platyhelminthes show the following parasitic adaptation for a parasitic mode of life:

  1. The epidermis is absent in them. They develop a resistant cuticle for protection.
  2. They have developed adhesive organs (organs for attachment), like suckers and hooks. These organs are used for attachment to hosts.
  3. There is a degeneration of the muscular system and nervous systems.
  4. They depend on the host for food. So their digestive system has become simplified.
  5. They have a complex reproductive system. They produce a large number of ova (eggs). So that their generations remain to continue.
  6. They show complex life cycles. They spend their lives in more than one host during their life cycle. It is an important parasitic adaptation.

Infestation

Tania or tapeworm show the following life cycle:

  • In Man: The development of a new Tania (tapeworm) begins inside in, the uterus of the female tapeworm. The uteri of the last segments or proglottids contain completely developed embryos. The embryo is rounded ¡n shape. It has sex-chitinous hooks. The fully developed proglottids break from the body. They pass out of the body of a man along with feces. The embryo shows limited movements of contractions.
  • In cow: It reaches a second host cow for further development. The parasite remains embedded in the voluntary muscles of the cow.

If improperly cooked beef (meat) of the cow is eaten by a person, the parasite enters the intestine of the man. It starts a new life cycle.

Disinfestation

Following measures can be taken for saving our bodies from infestation:

  1. If the parasite enters the intestine of a man, it becomes difficult to remove it. So, beef should be cooked properly before eating it. It will reduce the chance of entry of parasites into our intestines.
  2. If a parasite enters, then medicines should be taken for removing it. The parasites should be removed completely. If only ahead a parasite remains in the body, it can grow to form a new tapeworm.
  3. The physicians also give anema to the patient to fully remove the parasite.

Other Related Phyla:

  • phylum Porifera Characteristics & Examples
  • Phylum Chordata Characteristics & Classification
  • Characteristics of Phylum Echinodermata
  • Phylum Nematoda Characteristics, Examples
  • Phylum Mollusca Characteristics and Examples
  • Phylum Arthropoda Characteristics and Examples
  • Phylum Annelida Characteristics and Examples
  • Phylum Coelenterata/Cnidaria Characteristics and Examples
  • Phylum Porifera/Sponges With Examples & Characteristics
  • Phylum Protozoa: Characteristics & Groups/Classes

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