1. Chapter 27
Worms and Mollusks

2. Phylum:Platyhelminthes (flat) (worm)
Simplest bilateral symmetric animals showing a head and tail region.
3 layers: endoderm, ectoderm, mesoderm
Known as acoelomates (without a coelom)
coelom : a fluid-filled body cavity

3. General body structure:

4. Feeding Free-living flatworms can eat: Tiny aquatic animals
Dead animals
Single opening to function as a mouth and anus.
Possess a pharynx

5. Respiration, circulation, excretion
Breath through diffusion
Flame cells: specialized cells used for removing excess water.

6. Planarians (c. Turbellaria)
Free-living freshwater flatworm.
Possess a digestive tract, mouth, pharynx, and branched intestine.
Feed on small microscopic animals
No skeletal,circulatory,or respiratory system

7. Planarians continued Small brain with two nerve cords Hermaphrodites
Internal fertilization
Can also reproduce asexually.

8. Parasitic flukes (c. Trematoda)
Usually two or more hosts. (Page 687)
Primary host: human (site of asexual reproduction)
Causes the disease schistosomiasis

9. Tapeworms (c. Cestoda) Parasites. Example: beef tapeworm
Head region (scolex) : contains suckers and hooks used to attach to a host organism.
Proglottids : square body segments used for reproduction

12. Phylum: Nematoda (roundworms)
Long cylindrical bodies
Often covered with a thick cuticle
1 mm to 1 meter in length
Both free-living and parasitic
*** 2 body openings***
Major difference from the flatworms
Food and wastes will NOT be mixed

13. Form and function Eat small animals, bacteria, algae, fungi, etc
Exchange gases through diffusion
Possess a simple nervous system
Move through contracting muscles
Reproduce sexually

14. Trichina worm Causes trichinosis
Often present in pigs. Grow to about one millimeter in length and become cysts in pig muscles.
People eat contaminated pork and larval cysts develop into adults in human intestines.
New larvae can end up in human muscles.

16. Ways to prevent trichinosis:
Thoroughly cook pork products
Feed hogs uncontaminated feed
Freeze pork immediately after packaging

17. Filaria Roundworm that causes the disease elephantiasis.
Carried by mosquitoes
Infects bloodstream and blocks lymph nodes resulting in severe swelling.

18. Ascarid worms Affects more than 1 billion people
Affect people, horses, pigs, chicken, cattle, dogs, cats etc.

19. Pinworms and Hookworms
Most common nematode infection in N. America
Especially infants and toddlers.

20. HOOKWORMS Often will enter through the feet.
Common in areas where sewage disposal is inadequate

21. Phylum: Annelida Also known as the segmented worms.
The body is divided into separate body segments.
Marine,fresh water,and on land.
Parasitic and free-living. ex.

22. …more annelid facts “tube within a tube” body plan.
Closed circulatory system, 2 openings

23. respiration Aquatic annelids breathe using gills
Land-dwelling annelids breathe through the skin

24. excretion
Nephridia : excretory organs that filter nitrogenous waste in the ceolom.

25. Reproduction
Hermaphroditic. eggs and sperm released at the clitellum

27. First segment = prostomium
Earthworms
C. Oligochaeta
First segment = prostomium
Setae = small hair-like extensions on ventral surface used for locomotion.
Possess many “hearts”

28. The “hearts” of an earthworm:

29. Ecology of Earthworms Help to aerate the soil
Provide nutrients in to the soil in fecal matter
Participate in a wide range of food chains

30. Suckers on both ends of body
Leeches
Mainly freshwater.
Suckers on both ends of body
Saliva of leeches contain enzymes that prevent blood from clotting (anticoagulants)

31. Leech Anatomy
Attaches to prey with posterior sucker, and uses anterior sucker to “suck” blood.

32. Medicinal uses of leeches
Used to be used for “leeching” by early physicians to rid a sick person of “bad” blood.
Still used in surgery to prevent blood clotting and unwanted swelling due to excess blood.

33. Phylum: Mollusca Second largest phyla of animals after the arthropods.
Found in fresh water, salt water, and on land
ex.

34. Mollusk characteristics:
Soft bodies, 3 cell tissue layers
Many are used for food and jewelry
Possess a foot = large ventral muscle used for movement.
Most have a radula (exception: bivalves)
Mantle - fold of skin that surrounds the body organs

35. 1. bivalves 2 parts to their shells.
Strong adductor muscles to keep the shell closed
Incurrent siphon – carries water and food into the mantle cavity
Excurrent siphon – siphon where water is expelled.

36. Examples of bivalves:
clams and mussels
scallops
oysters

37. pearls Mother-of-pearl inner smooth part of bivlave shell.
Made primarily by oysters when a foreign object gets lodged inside between mantle and shell.
Come in many colors

38. Reproduction and nutrition
Bivalves are filter-feeders. (plankton and small invertebrates)
Separate sexes
Sperm is released by the excurrent siphon and enters a female via the incurrent siphon where fertilization takes place.

39. 2. gastropods slugs conch snails Largest class of mollusks
Most possess a single shell.exception: slug
slugs
conch
snails

40. 3. cephalopods Most advanced mollusks All are marine predators
Use tentacles to gather and manipulate food
Can swim rapidly by expelling a jet of water from their mantle cavity.
Some may discharge an inky fluid for defense
Octopus (8 arms) squid (10 tentacles)

41. examples:
nautilus
cuttlefish
octopus
squid