Please prepare to take notes.

Flatworms are placed in 3 classesFlatworms are placed in 3 classes

Class Turbellaria: Turbellarians are mostly free-living worms that range in length from 5mm-50cm.

Ex. Dugesia

Class Cestoda: The cestodes, or tapeworms, have long flat bodies made up of many reproductive units and have no digestive system.

Ex. Taenia

Class Trematoda: Trematodes are all parasitic flukes, and as adults they are almost all found as internal parasites of vertebrates

Ex. Schistosoma, Clonorchis

Characteristics

• Symmetry: Bilateral

• Cleavage: None

• Coelomate/ Acoelomate: Acoelomate because there is no cavity. It has a layer of mesenchyme instead of a coelom

• Integument: 3 layered body with layers closely packed to each other

Skeletal System

• Platyhelminthes have a hydrostatic skeleton

• Platyhelminthes rely on their hydrostatic system for support. The combination of the mesenchyme and the flexibility of the body wall makes it an adequate means of support. The body wall is a ciliated epidermis and does not possess a cuticle. Since there is no cuticle, the flatworms use their intracellular fiber and basal lamina to support the wall. This makes the wall more flexible than a body wall surrounded by a cuticle.

Muscular System

• Small aquatic tubellarians move with cilia

• Larger flatworms use muscular contractions for creeping and other types of locomotion

• Planarian dual glands and cilia

Digestive System

Class Feeding DigestionTurbellanians Feed on small

invertebrates

Mouth is used for both ingestion &excretion.

Mouth leads to pharynx and isfollowed by the gut

Some have intestines Digestion begins extracellularly Phagocytosis

Cestodes Feed on host (intestineof a vertebrate animal)

Possess no gut or simple gut No mouth or digestive tract Absorb food from environment Digestion is intracellular

Trematodes Feed on host tissuethrough pharynx

Contain mouth and simple gut Digestion is extracellular and then

intracellular

Feeding and Digestion

• (Above) Taenia solium• (Left) The mouth of

Taenia pisiformes

• (Right) Cestoda - Taenia pisiformis - Scolex, and interior suckers of a

tapeworm.

Circulatory System

• Flatworms lack a specialized circulatory system, thus they use….

Respiration

• Flatworms lack any specialized structure for gas exchange, so it occurs by…..

Can you guess??

Did you guess Diffusion??Have you guessed it yet??

Excretory System

• The Excretory System is a network of fine tubules

• Side branches consist of flame cells which move water towards exit pores

• This system regulates water balance

• Metabolic waste leaves by diffusion

Turbellaria - Flame cell -

protonephridia.

Nervous/ Sensory System

• Generally Diffuse

• Longitudinal Nerve Cords

Turbellaria - Bdelloura candida - Detail of the anterior end showing the brain, eyespots and the longitudinal nerve cords. Anterior branches of the intestine

are also visible.

Turbellaria-The Nervous system of a Dugesia.

Reproductive System

• Simple & Complex• Asexual (Hermaphrodites)

Structure of Amphilinidea (above)

Larvae (left)

Reproductive System

• From Left to Right: A) Cestoda - Taenia pisiformis - Immature proglottid showing the developing reporductive structures. B) Cestoda - Taenia pisiformis - Mature proglittid showing the main reproductive structures

including ovary, vitelline gland, testes,and ducts. C) Cestoda - Taenia pisiformis - Gravid (ripe) proglottid of a tapeworm showing the genital pore and the eggs contained in the proglottid.