Unsegmented Worms Flatworms and Roundworms Biology 11 Worms

Unsegmented Worms: Flatworms and Roundworms Biology 11

Worms • Divided into 2 Groups – Unsegmented • Flatworms • Roundworms – Segmented • Annelids

Phylum Platyhelminthes • Platy= flat • Helminth=worm • The Flatworms

Characteristics Acoelomates (no fluid filled space) Unsegmented body (not divided into sections) Live in aquatic habitat (streams, lake, oceans) Free living or parasitic Cephalization- concentration of sensory organs at one end • Bilaterally symmetrical • • •

Germ Layer • 3 cell layers- ectoderm, mesoderm, endoderm • Have a two way digestive system (lack an anus)

Class Tubellaria • Free living flatworms • Marine and fresh water (a few terrestrial) • Reproduce asexually by fission and sexually are hermaphrodites

Class trematoda • Parasitic flukes • Live as external and internal parasites on fish and other animals • Complex parasitic life cycle involving hosts • Hermaphrodites

Class Cestoda • Parasitic tape worms • Live in intestines of vertebrates • Have scolex in “head” section that have sections called proglottids – Contain reproductive organs and fertilization takes place inside – Mature proglottids detach and pass out of the intestine

Phylum Nematoda • The roundworms • Found in soil, marine, and fresh water

• Cylindrically shaped • Bilaterally symmetrical • 3 body layers- have pseudocoelom

• One way digestive system – Have mouth and anus • No circulatory or respiratory system – Fluid in pseudocoelom distributes food and oxygen • Have nerve ring around pharynx (no brain) • Have separate sexes

EXTREME HEEBY–JEEBIES AHEAD!

Roundworms found in dog poop

Inside a chicken’s intestine

Feeding • Most are free living carnivores/omnivores • Have pharynx • Can be parasites in plants and animals

Respiration and Circulation • Diffusion of gases through body walls

Excretion • Metabolic wastes diffuse through body walls • Undigested wastes through anus

• Filarial worms • Tropical Asia • Mosquito carries worms from host to host • Cause elephantiasis