1. FLAT WORMS

2. Phylum Platyhelminthes
Simple animals with soft leaflike or ribbonlike bodies, and includes flatworms, flukes, and tapeworms
Around 20,000 species
Body is unsegmented
Bilaterally symmetrical
Called “flatworms” because bodies are flattened dorso-ventrally

3. Phylum Platyhelminthes
Acoelomates-solid bodies without a lined body cavity; internal organs lie in a loose tissue called parenchyma
3 body layers: ectoderm, mesoderm, endoderm
Show cephalization (concentration of sensory organs at anterior or head end)
No circulatory system; body cells exchange oxygen & carbon dioxide directly with environment by diffusion

4. Phylum Platyhelminthes
Single opening into gastrovascular cavity: two-way digestive tract
In some a tubular pharynx can be projected
Mouth located at the front, ventral end
Water balance is maintained by excretory tubules (protonephridia) equipped with flame cells

5. Phylum Platyhelminthes
Nervous system: brain and nerve cords extending along the body
Circular, longitudinal, and other muscle fibers enable turning, twisting, and folding of the body
Free-living flatworms move by means of a ciliated epidermis and undulations of the body
Parasitic flatworms have thick cell layer called tegument covered by a nonliving cuticle covering their bodies as protection inside hosts

6. Phylum Platyhelminthes
Mostly hermaphrodites
Sperm and egg are exchanged during mutual copulation; internal fertilization
Asexual reproduction by fragmentation and regeneration
Parasitic species have complex life cycles - with several larval stages often with two or more different hosts

7. Classification Class Turbellaria Class Trematoda (flukes)
Dugesia (planarian)
Class Trematoda (flukes)
Schistosoma
Class Cestoda (tapeworms) 7

8. Class Turbellaria (Planaria)
Most are marine but include freshwater planarian (Dugesia)
Spade-shaped anterior end with light-sensitive eyespots
2 clusters of nerve cells (ganglia) to form a simple brain and a nerve net
Capable of simple learning

9. Class Turbellaria (Planaria)
Move by cilia
Feed by scavenging or protozoans
Mouth located at the end of muscular tube called the pharynx which is extended when feeding
Flame cells help remove wastes to excretory pores

10. Class Turbellaria (Planaria)
Hermaphrodites that cross-fertilize eggs; deposited into a capsule until hatching in 2-3 weeks
Reproduce asexually by fragmentation

11. Class Turbellaria (Planaria)
Brain
Eyespots
Pharynx
Nerve Cords
Gastrovascular Cavity
Mouth

12. Class Trematoda (Flukes)
Includes parasitic flukes
Most around 1 cm long and oval shaped
Require a host to live
Have oral and ventral suckers to cling to host & suck blood & body fluids
Endoparasites: live inside a host
Ectoparasites: live on outside of host

13. Class Trematoda (Flukes)
Covered in tough, unciliated tegument
Nervous & excretory systems like turbellarians
Hermaphrodites
Long, coiled uterus stores & releases 10,000+ eggs
Eggs released through genital pore & develop into larva

14. Class Trematoda (Flukes)
Life cycle of sheep liver fluke (Fasciola hepatica):
Adult liver flukes live in sheep liver & gall bladder where they mate & form eggs
Eggs enter intestines, pass out with feces, & hatch in water
Larva enter snails, asexually multiply, then leave snail & form cysts
Cysts (dormant larva with hard, protective covering) clings to grass
Sheep ingest cysts when they eat grass
Cysts hatch in digestive tract & bore through intestines into bloodstream
Mature and reproduce in the liver

16. Class Trematoda (Flukes)
Schistosomiasis: disease caused by parasitic blood flukes (Schistosoma); infects people in Asia, Africa, and South America causing intestinal bleeding and tissue decay that can result in death

17. Class Cestoda (Tapeworms)
Adapted for parasitic life
Tough outer tegument prevents being digested by host
Scolex: anterior end, contains hooks & suckers for attachment to intestine of host

18. Class Cestoda (Tapeworms)
Long, ribbon-like bodies up to 12 m in length
Nervous system extends length of body but lacks sense organs
Lacks mouth and digestive tract; absorbs digested nutrients from host
Grows by making body segments called proglottids

19. Class Cestoda (Tapeworms)
Each proglottid produces eggs & sperm that cross-fertilize with other segments & also self-fertilize (hermaphrodites)
Oldest, mature proglottids containing eggs at posterior end; break off & pass out with feces

20. Class Cestoda (Tapeworms)
Life cycle of beef tapeworm:
Cattle eat grass with proglottids containing fertilized eggs
Eggs hatch into larva & bore through cow’s intestine into bloodstream
Larva burrow into cow’s muscle & form cysts
Humans eat beef (muscle) & cysts travels to intestines
Cyst breaks open & adult beef tapeworm forms