Phylum: Platyhelminthes

Class: Cestoda

By: Mr. “Conferences” Chapman

CestodaClass Cestoda – tapeworms. Tapeworms are parasites that live in the digestive systems of vertebrate animals.

ScolexProglottids

Body Structure

Scolex (head)Proglottids (body segments). Strobillus - The entire length of the tapeworm’s body, excluding the scolex.

These are real tapeworms.Scolex

Proglottids

Since tapeworms live in the intestines of their host, they must be able to hold on to the intestinal wall. If they don’t they will move out of the host’s intestines with its wastes. A series of four suckers and ring of hooks on the scolex anchor the tapeworm to the host’s intestines.

The photographs at the left and right show the suckers and hooks on the scolexes of living tapeworms.

Body StructuresSince tapeworms live in the intestines of their host, they must be able to hold on to the intestinal wall. If they don’t they will move out of the host’s intestines with its wastes. A series of four suckers Rostellum - ring of hooks on the scolex anchor the tapeworm to the host’s intestines.

Although tapeworms exhibit cephalization, they have no eyespots. They also have lost their digestive system to evolutionary change. Because they live in their host’s intestine, they are surrounded by food. Molecules of food simply diffuse into the tapeworm’s cells from its environment.

CestodaSome tapeworms grow quite long. One species that parasitizes horses has been known to attain a length of 75 feet.

Cestoda

The length is determined by the number of proglottids that remain attached to the body. Mature proglottids break off and pass with the host’s feces.

CestodaLiving inside a digestive system can be hazardous. Digestive enzymes would simply dissolve most worms. Tapeworms have a waxy cuticle that covers their ectoderm. It is impermeable to the enzymes.

CestodaFlatworms are hermaphroditic. Each proglottid is one complete reproductive system. In these illustrations you can see both male and female reproductive structures.

CestodaSexual reproduction occurs when two tapeworms align, side by side, exchanging sperm through the genital pore (atrium). Eggs and sperm usually mature at different times so that a tapeworm doesn’t fertilize its own eggs. This insures genetic variation.

CestodaWhen the eggs in a proglottid are fertilized, the proglottid is considered “gravid”.

TapewormsWhen a gravid proglottid is at the end of the worm, it breaks off and wiggles out the host’s rectum. It then dries, splits open and spills out its eggs which are injested by a new host.

CestodaThe red and yellow object drawn on this photograph is a wooden match stick to show the size of proglottids that have broken free from the body of the tapeworm.

If your dog has tapeworms, the best way to detect them is to look around its rectum for the dried rice-like proglottids that get caught in the dogs fur.

The END