1. Latin for “Little rings” Segmented Worms
Phylum Annelida
Latin for “Little rings”
Segmented Worms

2. Segmentation
Repeating, specialized sections for different purposes or functions
Coelom is divided into separate compartments by partitions
Septa
Enables different compartments to contract or expand independently
Duplication of some of the organ systems between each segment provides insurance against injury

3. Taxonomy Class Polychaeta Class Hirudinea Class Oligochaeta
many bristles
Class Hirudinea
leeches
Class Oligochaeta
earthworms

4. Class Polychaeta - “many bristles”
Mostly marine worms
Have paddle-like appendages on sides
“parapodia”
Used for movement and respiration
Some have bristles to aid in defense

5. Bristleworm – many setae

6. Class Polychaeta Have antennae Have specialized mouthparts for feeding
Sense the environment
Have specialized mouthparts for feeding
Jaws (free swimming predators)

7. Class Polychaeta Some free living Some are sessile E.g. Nereis
Predatory
Some are sessile
live in tubes made of calcium, silica (sand) or protein
Filter feeders

9. Class Hirudinea Smallest class of Annelids (~300 species) Leeches
Suck vertebrate blood
Carnivorous
Powerful suckers at both front and back ends

10. Leeches No setae or parapodia Classified as a parasite
Have suckers at anterior and posterior ends
Move by “looping”:
Attach anterior sucker then pull rest of body forward
Classified as a parasite
Secrete an anaesthetic that prevents the host from feeling their presence
Secrete an anti-clotting agent
If undisturbed, a leech can ingest 10 times its own weight in blood

11. Class Oligochaeta Earthworms Tubifex (sludgeworm)
Found in soil and freshwater
Some types are found in the ocean
Tubifex (sludgeworm)
Can survive in polluted sediments, areas with little oxygen

12. Oligochaeta anatomy

13. Oligochaeta anatomy

14. Movement
Requires coordinated movement between the circular and longitudinal muscles
To move, the worm:
anchors middle segments using setae
contracts circular muscles in front of the anchored segments
this “squeezes” the fluid in the coelom which in turn causes the worm to “stretch” forward
the worm then anchors the anterior end, releases the middle and uses the longitudinal muscles to pull forward the posterior end
Made possible by segmentation

15. Movement

16. Feeding and Digestion Ingest soil as they burrow
Prostomium – flap of skin that covers the mouth when not feeding
Mouth – where soil enters the worm
Pharynx – muscular region that forces soil through esophagus into the crop
Crop – serves as temporary storage
Gizzard – muscular “blender” that grinds soil and organic matter

17. Feeding and Digestion
Intestine – long “tube” that absorbs any nutrients in the ground-up soil
has a special fold called a Typhlosole
increases the surface area of the intestine so that nutrients can be absorbed more efficiently
Anus – where any undigested material exits the worm = “worm manure”

18. Feeding and Ecology Earthworms are decomposers
Breakdown organic matter and
Release nutrients into soil , thus fertilize it
Loosen soil as they burrow and
Aerate it (increase its oxygen content)

19. Feeding and Digestion
prostomiumm

20. Circulation Closed circulatory system
transports oxygen, carbon dioxide, nutrients and wastes through the body of the earthworm
Ventral and Dorsal blood vessels
Blood is forced through blood vessel by contraction of vessels and 5 aortic arches

21. Circulation

22. Respiration No specialized respiratory organs
Oxygen and Carbon dioxide diffuse directly through skin and into small blood vessels
Only if skin is moist

23. Excretion Nephridia or Nephrostome act like kidneys Nephridiopores
remove waste and control water levels in blood
Nephridiopores
pores on ventral side of worrm
release waste and excess water
each segment except first three and last one have nephridia and nephridiopores

24. Excretion

25. Nervous System Chain of ganglia connected by a ventral nerve cord
Most body segments have a single ganglion
Have an anterior cerebral ganglia (brain!)
Can respond to light, touch, chemicals, moisture, temp, vibrations

26. Nervous System

27. Reproduction
Hermaphroditic
individual worm cannot fertilize own eggs

28. Reproduction The “Position”
head to tail, ventral surface to ventral surface
The “Transfer”
clitellum secretes mucus
each earthworm injects sperm into the mucus
mucus moves into pouch-like seminal receptacle of each worm
The “Delivery”
several days later the worm secretes a tube of mucus and chitin (thick carbohydrate) from clitellum
as the worm moves the tube “picks” up eggs and carries it to sperm to be fertilized
The “Result”
tube closes up to form protective case and 2-3 weeks “baby” worms hatch

29. Review