1. Phylum Annelida

2. Phylum Annelida “little ring” Segmented worms 15,000 species
Marine worms
freshwater worms
terrestrial worms
Leeches
worldwide distribution
Soft body
Repeating segments allow independent movement

3. Size of Annelids <1mm  many meters
Megascolides australis up to 7.5 m!

4. Architectural patterns of animals
Architectural patterns of animals. These basic body plans have been variously modivied during evolutoinary descent to fit aimals to a great variety of habitats. Ectoderm is shown in gray, mesoderm in red, and endoderm in yellow
Fig. 9.9

5. Fig. 9.9

6. Trochophore larva

7. Characteristics of Phylum Annelida
triploblastic
schizocoelomate

8. In enterocoelous formations, the ceolom comes from pouches of the primitive gut (archenteron)
Fig. 9-13, p188

9. Characteristics of Phylum Annelida
Coelom partitioned by walls (septa)
Serial (repeating) segmentation= metamerism
Each segment= metamere/ somite

10. Development of Metameric, Coelomic Spaces

11. Characteristics of Phylum Annelida
External evidence of septa= circular grooves called annuli (rings)
Septa
annuli

12. Advantages of metamerism
greater flexibility of movement, compare to nematode
Components organ systems repeated w/i segments
(repeated excretory, nervous, circulatory structures)
Built-in redundancy- increases survival

13. Note:
Not all organ systems are metameric
ie, digestive system extends the length of the organism and is differentiated along its length

14. Characteristics of Phylum Annelida
Greater flexibility demands greater fine motor skills
Highly developed, centralized nervous system
brain
Ventral nerve cord
Ganglion in each metamere

15. Movement in Phylum Annelida
Fluid-filled coelom (except Subclass Hirudinea) = hydrostatic skeleton
Longitudinal and circular muscles

16. Characteristics of Phylum Annelida
Closed circulatory system (except some leeches)
Blood vessels and aortic arches (“hearts”)
Branch to every metamere

17. Excretory System of Annelids
Consists of paired metanephridia (in most)
Excretory tubes with ciliated funnels that remove waste from the coelomic fluid
open to the outside via excretory pores.

18. Phylum Annelida: Classes
Class Polychaeta
Class Clitellata
Sublass Oligochaeta
Subclass Hirudinea
Fan Worms clip

19. Class Polychaeta poly = many; chaeta = bristles Mostly marine
Example: Neries video
Mostly dioecious

20. Class Polychaeta (cont’d)
Parapodia
fleshy segmented appendages for locomotion & breathing
have numerous setae at ends of parapodia
Fireworm (Hermodice carunculata)

21. Class Polychaeta (cont’d)
Gas exchange across parapodia

22. Class Polychaeta (cont’d)
parapodia have numerous setae at ends
Tiny chitinous bristles
Chitin= tough, flexible polysaccharide; not soluble in water
Provide anchorage
Swimming
Fireworm (Hermodice carunculata)

23. Class Polychaeta (cont’d)
well differentiated head (prostomium) with specialized organs (eyes, jaws)

24. Class Polychaeta (cont’d)
Many are euryhaline (able to tolerate a wide range of salinity conditions).
Live under rocks, coral crevices, abandoned shells.
Serve as the basis for many marine food chains.

25. Class Clitellata
Earthworms and leeches
Few/no setae
Possess clitellum

26. Class Clitellata (cont’d)
Clitellum
secretes mucus for cocoon, copulation

27. Class Clitellata (cont’d)
monoecious, cross-fertilization

28. Subclass Oligochaeta oligo = few; chaeta = bristles
Terrestrial, freshwater, some marine
Example: earthworms, night crawlers

29. Subclass Oligochaeta (cont’d)
Prostomium lacks sensory structures
Parapodia are absent
Prostomium  2. Mouth   3. Buccal cavity  4. Pharynx  5. Esophagus   6. Nephridia  7. Seminal vesicles  8. Dorsal blood vessel  9. Ventral blood vessel10. Aortic arches11. Suprapharyngeal ganglion12. Circumphar. connective13. Ventral nerve cord
bioweb.uwlax.edu/.../ earthworm_model_1a.htm

30. Subclass Oligochaeta (cont’d)
Feeds on organic or vegetable matter in soil
May be as many as 50,000/acre
Earthworms very beneficial in aerating the soil.
capable of recycling up to 18 tons of soil/acre annually
food

31. Do these questions now…
The coelomic cavity of annelids is usually divided by walls called ________
What is metamerism?
What are the advantages of metamerism?
Is any part of the annelid not metameric? What part?
To what class do earthworms and leeches belong?

32. Subclass Oligochaeta (cont’d)
Gas exchange across moist skin  to circulatory system

33. Subclass Hirudinea Leeches Mostly freshwater
possess clitellum – apparent only during reproduction
have annelid characteristics but generally lack setae
Monoecious, cross-fert.
Generally dorsoventrally flattened

34. Subclass Hirudinea (cont’d)
Predatory
Attach to host via 2 suckers

35. Subclass Hirudinea (cont’d)
Locomotion
More complex muscle system- includes oblique + dorsoventral muscles
“inchworm” movement via suckers

36. Subclass Hirudinea (cont’d)
Have a fixed number of metameres
Internal septa are lacking
coelom functions as a single, large chamber with connective tissue, muscle, and spaces

37. Subclass Hirudinea (cont’d)
Gas exchange across skin (in most)

38. squeamish?

39. Medicinal leech Attach via suckers, pierce skin with sharp proboscis.
Leeches cure
Attach via suckers, pierce skin with sharp proboscis.
Proboscis resembles 3 circular saw blades.
Salivary glands secrete local anesthetic and an anti-coagulant.
remove hematomas resulting from surgery
15 ml blood/meal
hematomas (areas of blood leakage)