Phylum Platyhelminthes

General Characterisitics Bilateral symmetry Acoelomate Triploblastic Dorsoventrally Flattened Un-segmented bodies Cephalization (has a head)

Actual organ systems present Characteristics Cont. 20,000 species Actual organ systems present Nervous, Digestive, Excretory

Taxonomy 3 Classes Class Turbellaria Class Trematoda Class Cestoidea

Class Turbellaria Planarians Free-living bottom-dwellers in aquatic environments few terrestrial species in the tropics 3,000+ species Vary widely in color, size, and shape Terrestrial ones can be up to 60cm

Body Description 3 Layers Ectoderm Mesoderm Endoderm Acoelomate- have a solid mass of mesoderm cells between the ecto- and endo- derms

Acoelomate Design

Locomotion As bottom dwellers the flat worms glide over the substrate (ground) Use cilia and muscular contractions Lay down a sheet of mucous as they travel (like slugs)

Body Systems Digestive- can be simple or complex Pharynx: muscular ingestion organ Some digestion takes place outside the body Enzymes secreted on food particles; helps to break them down so the pharynx can swallow them easier.

Digestive System

Body System Con’t Respiratory- have none gases are exchanged over the epidermis Circulatory Protonephredia: fine networks of tubes that run the length of the body and collect waste Flame cells: bulb-like structures that force waste out of the body through openings called nephridiopores.

Excretory System

Nervous: detecting and responding to environment Simple: nerve net w/ Statocysts- sense gravity Complex: nerve net and two main nerve cords with ladder like connections between Auricles: chemoreception Ocelli: eyespots; detect light

Nervous System

Reproductive: Most hermaphrodites Exhibit both sexual and asexual Asexual- transverse fission Sexual- mutual sperm transfer

Planarian Body Systems

Class Trematoda Parasitic flatworms (called flukes) 1mm to 6cm in size Most infect internal organs – can be blood or virtually any other organ

Primary host = the host in which a parasite reproduces sexually Intermediate host = the host in which asexual reproduction occurs

Fish Flukes 30 million people infected in Asia Caused by eating raw or improperly cooked fish Resides in liver bile ducts

Causes fever, weight loss, joint aches, inflammation, hives, weakness, diarrhea, and an enlarged liver.

Chinese Liver Fluke

More Flukes Liver Flukes Live in the liver bile ducts of sheep and humans Host infected by eating aquatic vegetation (watercress)

Schistosomes: blood flukes Millions infected worldwide Causes rash, fever, chills, inflammation, liver and spleen enlargement.

Schistosoma mansoni - multiple host: Primary host = human Intermediate host = snail Causes Schistosomiasis -in humans; decays lungs liver, spleen, or intestines, occurs in tropical areas with poor sanitation/sewage.

Blood Fluke

Class Cestoidea Tapeworms 3,500 species All are endo-parasites of vertebrates

Lack a mouth and digestive tract Body consists of 3 main parts scolex: hold fast structure Strobila: the neck region Proglottids: reproductive sacs that make up 90 percent of the body

Each mature proglottid is a hermaphrodite Testes produce sperm, fertilize the eggs to produce a zygote Zygotes are passed out through the feces.

Sometimes, a dormant, protective cyst is formed in the intermediate host muscles ****This is why you should never eat incompletely cooked meat.

Tapeworm Life cycle

Tapeworm Life Cycle