Platy = flat Helminth = worm Platyhelminthes Platy = flat Helminth = worm

Taxonomy Phylum Platyhelminthes Kingdom Animalia Phylum Platyhelminthes Class Turbellaria Class Trematoda Class Cestoda (planarians) (flukes) (tapeworm)

Platy = flat Helminth = worm Flatworms flatworm biology

General Characteristics Body is flattened dorsoventrally (from back to belly) Acoelomates: have no true body cavity Most are parasitic but a few are free-living Three body layers: ectoderm, mesoderm, endoderm Cephalization: sensory organs are clustered a head region Simplest animals with bilateral symmetry

Body Plan Three body layers Digestive cavity Bilateral symmetry Acoelomates Have only 1 body opening- no anus

Digestion 2-way digestive tract Free-living: food enters through the mouth and pharynx Parasitic: suckers take in predigested food – no digestion is needed

Circulation and Respiration No circulatory system Gases diffuse through skin FLAME CELLS: cells that circulate water and nutrients

Sensory organs Eyespots (in some) Ganglia (bundles of nerves) Nerve cords

Movement Secrete mucus and use cilia on their ectoderm layer to glide along surfaces Use muscle contractions to twist and turn flatworm moving

Reproduction All are hermaphrodites that do NOT fertilize their own eggs (except tapeworms) All can reproduce sexually as well Asexual: budding, fission, regeneration Sexual: monoecious but don’t fertilize their own eggs

Ecological Importance Most are parasitic (Endoparasites) Free-living forms live in water and are a food source for many other animals

Class Turbellaria Planarians and marine flatworms All are free-living Live in all water environments (lakes, ponds, oceans etc.) Planarians worlds weirdest

Class Trematoda Flukes All are parasitic Found in warm, tropical areas Can make people extremely sick or even cause death snail parasites blood flukes

Intestinal fluke

Liver Fluke

Class Cestoda Tapeworms All are endoparasites Live in the intestines of mammals Has a scolex and hooks to attach to the host Contracted by eating undercooked meat tapeworms tapeworm2 tyrabanks human parasites

Videos parasites in fish parasite in eye Platyhelminthes mind controlling parasites