The phylum is Platyhelmenthus The three classes are 1. turbellaria 2. trematoda 3. cestoda

Platyhelminthes is a phylum composed of three classes of flatworms.

The class Turbellaria planarians is free-living, while the remaining classes including the Trematoda flukes and Cestoda tapeworms are parisitic.

Members of the phylum Platyhelminthes are dorsoventrally flattened

with a triploblastic body composed of three different tissue layers: ectoderm, endoderm, and the mesoderm. These animals are bilaterally symmetrical, meaning that a slice directly through the middle can produce two mirror images. This phylum demonstrates an organ-system level of organization. The front or anterior portion of the body bears most of the sense organs as compared to the rear or posterior of the body. Most flatworms have a single opening to the digestive tract and they have no respiratory or circulatory systems; but are simple and flat enough so diffusion is sufficient for these processes. Protonephredia and flame cells regulate water balance.

The best known member of the class Turbellaria is the free-living

planarian, duqesia They are usually found in slow-moving streams near stones, leaves or debris. The head of these animals has lateral tactile projections termed auricles. There are also photoreceptor sensory organs termed ocelli on the anterior dorsal surface. Their nervous system is based on two longitudinal ventral nerve cords connected by the anterior ganglia, or primitive brain. This concentration of sense organs in the anterior end is termed cephalization.

Planarians secrete a slime track over which they glide. Gliding is

accomplished by beating the epidermal cilia in the slime track.

These flatworms ingest food by means of a tube-like pharynx located

on the midventral line. Digestion begins extracellularly with enzymes secreted onto the food before it is sucked into the intestine by the pharynx. The intestine may have lateral branches, adding surface area for increased absorption of nutrients. The mouth, pharynx, and intestine make up the entire digestive tract.

Water balance or osmoregulation is maintained by protonephridia

which terminate in specialized flame cells. A cross section of duqusia will show the ectoderm which produces the epidermis. The layer surrounding the digestive tract is derived from endoderm. The space between the two layers is filled with tissues from the mesoderm.

Members of the class Trematoda consist of the parisitic flukes . The

flukes live within one or more host animals during their life cycle. They have a well-developed digestive system with the mouth at the anterior end. They are characterized by a thick cuticle as well as one or more suckers surrounding the mouth. These suckers are used for attachment to the host's internal body surface. These organisms are typically hermaphrodidic (have male and female sex organs). With the aid of a drawing of clonorchis sinesis (a human liver fluke) locate the: oral sucker, pharynx, esophagus, excretory bladder, ovary, uterus, seminal receptacle, testes, seminal vesicles and vas deferens.

Members of the class Cestoda are endoparisitic tapeworms which

completely lack a digestive tract. At the anterior end a scolex possessing hooks and suckers is found which attaches to the host's digestive system. Posterior to the scolex is the neck region which leads to sections termed proglottids. Each proglottid possesses both male and female reproductive organs. Farther down, the gravid proglottids contain thousands of fertilized eggs. In the drawing and pictures of Taenia pisiformis (tapeworm) observe the scolex with hooks and suckers, proglottids, ovary, testes, uterus, and excretory canals. _____________________________________________________________________ hopefully that is enough information for you it is what i used for my science report last year!!!!!!!!!!!!!!!!....................

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