1. Vocabulary List Crop Gizzard Nephridia Setae Clitellum Metamerism
Parapodia
Tagmatization

2. Chapter 13
Phylum Annelida

3. Characteristics of Phylum Annelida
Body is metameric (segmented arrangement of body parts)
Bilateral symmetry and wormlike
Closed circulatory system
Includes over 10,000 species of segmented worms-most are marine
Triploblastic Coelomates

4. Characteristics of Phylum Annelida
Live everywhere except in frozen soil of polar regions and in the sand of dry deserts
Include earthworms, marine worms, and parasitic leeches
Different from flatworms and roundworms because they are segmented and have a coelom

5. Taxonomy of Annelida: Kingdom Animalia Phylum Annelida
Class Polychaeta
Class Clitellata

6. Class Clitellata Characteristics: Two subclasses:
Clitellum in cocoon formation
Monoecious
Few or no setae
Two subclasses:
Oligochaeta (earthworms)
Hirudinea (leeches)

7. Subclass Oligochaeta Over 3,000 species Habitat: Freshwater
Few estuarine
Some marine
Terrestrial
live in soil
during hot weather, may burrow 3 meters down

8. Lumbricus terrestris Earthworm No parapodia Cuticle covers body
Body segmented with short setae
Clitellum:
Swollen set of segments in the anterior half
Will secrete mucus during copulation
Forms a cocoon

10. Subclass Hirudinea Leeches About 500 species Most are freshwater
Predators of small invertebrates
Feed on body fluids of vertebrates (parasites)

11. Class Polychaeta Largest class (more than 5,300 species) Mostly marine
Habitat:
ocean floor
Under rocks, shells
Crevices of coral reefs
Burrow through substrate (tubeworms)

12. Segments with extensions called parapodia Numerous setae (bristles)
First body segment called the peristomium:
has mouth, protomium, sensory tentacles (cirri) & 2 to 4 pairs of eyes
May be predators, herbivore, scavengers, or filter-feeders

14. Metamerism & Tagmatization
Segmental arrangement of body parts in an animal.
It influences every aspect of annelid structure & function
The compartmentalization of the body has resulted in each segment having its own excretory, nervous, and circulatory structures.
The specialization of body regions in a metameric animal.
Although it is best developed in the arthropods, some annelids also display tagmatization.
Greek “tagma” means arrangement

15. Advantages of Metamerism (segmentation)
Creation of hydrostatic compartments
Lessens the impact of injury
Permits the modification of certain regions of the body for specialized functions, such as feeding, locomotion, and reproduction.
Hydrostatic compartments allow a variety of advantageous locomotor and supportive functions not possible in nonmetameric animals that use hydrostatic skeletons. Each segment can be controlled independently of distant segments, and muscles can act as antagonistic pairs within a segment.
If one or a few segments are injured, adjacent segments set off from injured segments by septa, may be able to maintain nearly normal functions, which increases the likelihood that the worm, or at least a part of it, will survive the trauma.

16. Feeding & Digestion
Running through all earthworm segments from the mouth to the anus is the digestive tract (a tube in a tube)
Food and soil taken in by the mouth pass through the pharynx into the crop, where they are stored until they pass to the gizzard (gizzard is a muscular sac containing hard particles that help grind soil and food before they pass into the intestine).

17. Feeding & Digestion Nutrients are absorbed from the intestine
Undigested material passes out of the worm’s body through the anus
Parasitic annelids have pouches along the digestive tract that hold enough food to last for months!

18. Circulation
Closed circulatory system. Oxygen and nutrients move to various parts of their bodies through their blood vessels.
At the same time carbon dioxide and metabolic wastes are removed from the blood and excreted.
Some of the vessels at the anterior end, or head, are large and muscular and serve as hearts that pump the blood.
The blood moves toward the anterior end of the worm in the dorsal blood vessel and toward the posterior end in the ventral blood vessel.
An earthworm has five hearts that pump blood through its circulatory system!

19. Respiration & Excretion
Segmented worms have 2 nephridia in almost every segment.
Cellular waste products are collected in the nephridia and are transported in tubes through the coelom and out of the body.
Nephridia also function in maintaining homeostasis of body fluids of annelids, ensuring that the volume and composition of body fluids are kept constant.

20. Response to Stimuli
Anterior segments are modified for sensing the environment
You might have seen an earthworm quickly withdraw into its burrow when you shine a flashlight on it or step close to it….these observations show that earthworms can detect both light and vibrations.

21. Movement
When an earthworm moves, it contracts circular muscles running around each segment.
This squeezes the segment and causes the fluid in the coelom to press outward like paste in a tube of toothpaste being squeezed.
Because the fluid in the coelom is confined by the tissues between segments, the fluid pressure causes the segment to get longer and thinner…
Next, the earthworm contracts the longitudinal muscles that run the length of its body.
This causes the segment to shorten and return to its original shape, pulling its posterior end forward and resulting in movement!

22. Movement
Many annelids have setae on each segment. Setae are tiny bristles that push into the soil and anchor the worm during movement.
By anchoring some segments and retracting others, earthworms can move their bodies forward and backward segment by segment!

23. Reproduction Annelids can reproduce both sexually and asexually.
Most annelids have separate sexes, but some, such as earthworms and leeches, are hermaphrodites.
Sperm are passed between two worms near segments called clitellum (a thickened band of segments).
It produces a cocoon from which young earthworms hatch.
Sperm and egg pass into the cocoon as it slips forward off the body of the worm.
After fertilization, the young are protected in the cocoon as they develop.
Some annelids reproduce asexually by fragmentation.
If a worm breaks apart, the missing parts can be regenerated.
Reproduction

24. Earthworm reproduction
Monoecious & Exchange sperm
Copulation: Two worms line up in opposite directions
Clitellum of one lines up with genital segments of other
Mucus holds worms together
Sperm travel from one to the other
Last 2-3 hours
After copulation, a cocoon is formed around worm
Mucus, food, eggs and sperm are deposited in the cocoon
Fertilization occurs in the cocoon
Worms back out of the cocoon and it drops to the ground
Hatching – takes a few weeks

26. Earthworms Probably the best known annelids
Used as bait for fishing and are found in garden soil.
Can eat its own mass in soil every day!
Earthworms ingest soil to extract nutrients…in this way, earthworms aerate the soil-they break it up to allow air and water to move through it (my mom always said, you know you’ve got good dirt if you find a worm)

27. Marine Annelids Include bristleworms and fan worms
Have head regions with well-developed sense organs, including eyes.
Most body segments also have a pair of appendages called parapodia that are used for swimming and crawling
Fan worms are sessile and filter feeders, they trap food in the mucus on their fan-shaped structures.
If there is a threat nearby, fan worms retreat into their tubes.
Marine Annelids

28. Leeches External parasites Flattened bodies and usually no setae
Most live in freshwater streams or rivers where they attach to the bodies of their hosts-including fishes, turtles, and humans.
Leeches attach to their hosts using front and rear suckers.
When a leech bites, it saliva contains chemicals that act as an anesthetic.
Other chemicals in the saliva reduce swelling and prevent the host’s blood from clotting.
They maintain blood flow after microsurgery.

30. Medicinal leeches