In details

Flatworm Classification


We will study reproduction according to each class. The approximately 20,000 flatworm species can be grouped into three broad classes:

  • Cestoda Class - endoparasites, usually with intermediate hosts. Example: Tapeworms
  • Trematoda Class - parasites, most life cycles include the presence of an intermediate host. Example: Schistosoma mansoni;
  • Turbellaria Class - Free-living animals, most of which are aquatic, only some terrestrial, are predators and scavengers. Example: planarians.

Turbellaria Class

They are free-living animals, have eyelashes for locomotion and a foliate appearance. An example of a representative of this class is the planary.

They are hermaphrodites and cross-fertilize, self-fertilization is rare. The two mating individuals are joined by the genital pores. Each introduces the penis into the genital opening of the other, exchange sperm and separate. Several eggs are fertilized and thrown out through the genital pore. The zygotes have a protective capsule and will hatch young planarians, showing a direct development.

The planarians have a great power of regeneration, and reproduce asexually per transverse fission. If we cut a planaria into several pieces, each one will be regenerate and give rise to a new individual.


Asexual reproduction by transverse fission.


If we cut a planaria into several pieces, each one will be regenerate and give rise to a new individual.

Trematoda Class

They are endo or ectoparasites. They have suction cups for attachment, one in the oral region, the other ventral. They have a protective cuticle in the epidermis and no eyelashes. They are hermaphrodites, but the S. mansoni It's dioecious. The female lives in a male cavity called the gynecophore channel. They do cross and internal fertilization. As hermaphrodite representative we have the Hepatic fasciola, which parasitizes the liver of sheep and eventually the human being.

Male and female (in the male ventral cavity) of Schistosome mansoni . Note the suction cup on the front side.

Cestoda Class

They are endoparasites with elongated body, represented by tapeworms. They have no eyelashes, the body is metamerized and have no digestive tract, feeding on diffusion of nutrients predigested by the host.
Tapeworms can reach up to 8 meters in length. Their body is divided into three parts: Head or sclex, which has suction cups for attachment to the host. THE Taenia solium presents hooks and suction cups; neck or neck, the most tapering and strobile region, responsible for the growth of the organism.

There are proglottids, structures that have female and male reproductive systems, that is, they are hermaphrodites. After fertilization the egg-filled proglottids detach and are eliminated with feces.

Diseases Caused by Platelminths

Schistosomiasis

Teniasis