1. The Invertebrates
The Worms

2. General Characteristics
soft-bodied, long, legless
bilateral symmetry
cephalization
a distinctive sensitive anterior region having a collection of nerve tissue with which to make decisions
three cell layers
epidermis – outer layer; protection and locomotion
mesooderm – middle layer; muscular contractions during locomotion
gastroderm – inner layer; lines the digestive track
Many phyla, we will look at 3 most common

3. Phylum Platyhelminthes
the “flatworms”

4. The Flatworms thin flattened body most are parasitic
tapeworms
flukes
some are free-living
planarians
3 classes

5. Planarians (Life process chart)
Class Turbeliaria – free-living
freshwater
approximately 1cm long
anterior region has cross-eyed eyespots on the dorsal surface that are sensitive to light

6. Planarians

7. Planarians
movement
cells on the ventral surface secrete slime and then the ciliated cells can move across the slimy surface
muscles in the mesoderm can contract to help with movement

8. Planarians nutrition eats small animals, eggs, liver
releases digestive enzymes out of its mouth and onto their prey
pharynx extends out of mouth and draws up the digested particles into the branched intestine
enzymes in the intestine break down the food further
food is diffused throughout the body
waste is egested through the pharynx

9. Planarians
excretion
flame cells – hollow bulbs located at the end of a system of tubes in the mesoderm, empty waste into the environment by the means of excretory pores
helps maintain water balance by excreting excess water

10. Planarians
Response
anterior mass of nervous tissue, ganglia, act as a “brain”
two longitudinal nerves extend from the “brain” and transverse nerves join the longitudinal nerves together
sensitive to touch, chemicals, light

11. Planarians
eyespots
longitudinal nerves
transverse nerves

12. Planarians asexual reproduction
fission: planarian can pull itself apart behind the pharynx and each half can regenerate into new animals
sexual reproduction
hermaphroditic: both male and female reproductive organs
cross-fertilize each other and release eggs enclosed in a capsule
eggs will hatch in about 1 months time

13. Planarians

14. Parasitic Flatworms depend on host for nourishment
harm their host, but do not kill them
few sense organs as adults
no external cilia in adults
thick tegument (protective covering)
suckers and/or hooks for attaching to the host

15. Parasitic FLukes Class Trematoda – The Flukes
Opisthorchis sinensis
Intermediate host - an animal that temporarily harbors the immature form of a parasite (snail)
cannot live outside of host for very long
Read page in textbook

16. Parasitic FLukes flukes sheep liver fluke mouth intestine sucker ovary
testes

17. Parasitic Tapeworms Class Cestoda – The Tapeworms
Do not resemble flukes
Pork tapeworm
Ribbon-like body that can be as long as 6m in length
Lives in intestines of a vertebrate host, animal or human
Scolex – small bulb-shaped head
Suckers and hooks on scolex attach worm to host

18. pork Tapeworms (cont.)
body is divided into proglottids that contains both testis and ovaries
no mouth or digestive organs
absorbs and uses only food that the host’s body has already digested
tegument protects it from harsh digestive juices
deprives host of food, but usually pose no physical dangers UNLESS
tapeworm grows so long as to clog the intestines
humans eat the proglottids and cysts form in their muscles