Phylum PlatyhelmenthesPhylum PlatyhelmenthesPlanarians, Flukes, & TapewormsPlanarians, Flukes, & Tapeworms

•Simple acoeleomatesSimple acoeleomates•Bilaterally Bilaterally symmetricalsymmetrical•Most flattened Most flattened "Dorsoventrally""Dorsoventrally"•Divided into 4 Divided into 4 classes:classes:

Class TurbellariaClass Turbellaria•Most free-living and Most free-living and non parasiticnon parasitic•Include Include planariansplanarians•Lack circulatory and Lack circulatory and gas-exchange organs.gas-exchange organs.•Simple excretory Simple excretory structures called structures called flame flame cellscells that maintain that maintain osmotic balance.osmotic balance.•Is Is cephalizedcephalized and has and has eye-spotseye-spots which are which are sensitive to lightsensitive to light•Feeds through ventral Feeds through ventral feeding tube called a feeding tube called a pharanxpharanx•Can reproduce Can reproduce sexually, or asexually sexually, or asexually through regeneration through regeneration

Planarian and assorted marine Planarian and assorted marine flatworms…flatworms…

Class Trematoda (Flukes)Class Trematoda (Flukes)• Similar in form to Similar in form to turbillariansturbillarians

• Many are parasitic. Many are parasitic. Example of Example of parasitic fluke is parasitic fluke is the the asian liver asian liver flukefluke

• Many have complex Many have complex life cycles life cycles including multiple including multiple hosts and hosts and alternation of alternation of generations.generations.

Life Cycle of the Liver FlukeLife Cycle of the Liver Fluke

Liver Flukes Cont’d…Liver Flukes Cont’d…

Liver Fluke encysted in a liverLiver Fluke encysted in a liver

Liver FlukeLiver Fluke

Class Cestoda (Tapeworms)Class Cestoda (Tapeworms)

• Parasitic flatwormsParasitic flatworms• Can grow to enormous Can grow to enormous

lengths (up to 20m)lengths (up to 20m)• Parasitize mostly Parasitize mostly

vertebrate hostsvertebrate hosts• Attach head named Attach head named scolexscolex

to intestinal walls of to intestinal walls of host, and abosrb host's host, and abosrb host's nutrientsnutrients

• Following scolex is a Following scolex is a series of repeating series of repeating structural units called structural units called proglottidsproglottids

• Mature proglottids Mature proglottids containing thousands of containing thousands of eggs are released with eggs are released with the host's feces to the host's feces to infect other organisms.infect other organisms.

Tapeworms cont’d…Tapeworms cont’d…