Unsegmented Worms Flatworms Flatworms Belong to the phylum

Unsegmented Worms

Flatworms

Flatworms • Belong to the phylum Platyhelminthes. (Plat = flat) • There are three classes: – Turbellaria – Trematoda – Cestoda

Examples of flatworms • Fluke Planaria Polycladids

Also…. . Tapeworms! • Yuck!

Characteristics of Flatworms • They are acoelomates (they don’t have body cavities) • They have bilateral symmetry • Show cephalization • Respiration through skin • Single opening to digestive tract (pharynx)

Reproduction • Asexual- Planaria can regenerate missing body parts • Sexual reproduction- make both eggs and sperm

Flatworm Body Plan

Class Turbellaria • • Spade-shaped head and two eyespots Eat protozoans Flame cells remove waste Are hermaphrodites (have male and female reproductive parts) • Can reproduce by regeneration • Are free-living

Class Turbellaria § Most forms marine most familiar species is the Planarian which is freshwater § Planaria are found in all freshwater habitats

Class Trematoda • Are parasitic flukes • Have suckers on both ends of the body • Can live inside or outside of host

Class Trematoda • Nervous and excretory systems like turbellarians • Hermaphrodites • Have complex life cycles

Schistosomiasis § Disease caused by parasitic flukes § Eggs are carried to the lungs, intestines, bladder and liver blocking blood vessels which can be fatal § Affects about 200 million mostly in Asia, Africa and South America § Disease best controlled using water treatment practices

Class Cestoda • Parasitic Tapeworms • Long, ribbon-like bodies • Absorbs nutrients from host • Scolex is used to attach to host

Tapeworm Anatomy

Roundworms

Roundworms • • • Belong to phylum Nematoda Pseudocoelomates (fluid filled body cavity) Slender bodies that taper on both ends Have mouth and anus Can be free-living or parasitic

Pinworms live in human intestines

Pinworms • Pinworms- most common roundworm parasite of humans in US; very high infection rate in school age children yet no serious threat and are easily treated

Ascaris roundworms • Ascaris- roundworm genus that parasitize pig, horse and human intestines; can overpopulate and block intestines

Hookworms • Hookworms are intestinal parasites • Cutting plates attach to host intestinal wall • Feed on host blood and can cause anemia, cause slow development if left untreated

Trichinosisa disease from eating infected pork

Cysts in Contaminated Pork

Filarial Worm Infections § Elephantiasis/ Filariasis - build up of fluid as a result of blockage in lymphatic vessels; limbs are very swollen, skin is thick and hardened; worsened by accompanying bacterial and fungal infections § Other filarial worms infect pets, known as heartworms if they infect cardiac muscle

Not all bad…. § Beneficial nematodes: organic pest control b/c they kill garden pests, bacteria and fungi by secreting their own bacteria § Controls Japanese beetles, & various roaches, weevils, maggots; § Doesn’t harm beneficial creatures like earthworms