1. Phylum Annelida The Segmented Worms
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2. Annelida Characteristics
Triploblastic
Organ level of organization
Bilateral Symmetry
Cephalization
Eucoelomate

3. Eucoelomate
Have a “true” body cavity that is completely surrounded by mesoderm
ectoderm
coelom
mesoderm
Gut
endoderm

4. Annelid Characteristics
the coelom
is a closed, fluid filled cavity that surrounds the gut
mesodermal membranes (mesenteries) suspend organs in the coelom

5. Annelida Characteristics
Protostome
Development is characterized by:
blastopore becomes the mouth
Spiral / determinate cleavage
Schizocoely

6. Annelida Characteristics
Metamerism
The body is made up of serially repeating, coordinated segments called metameres that are separated from one another by septa.
Each metamere contains sets of repeating organs
e.g. blood vessels, nerve cord, excretory organs

7. Metamerism
septa

8. Annelida Characteristics
Nervous system
2 cerebral ganglia
a ventral nerve cord with 2 ganglia per metamere.
In some species, sensory organs such as eyes, palps, and tentacles have arisen

10. Annelida Characteristics
Locomotion
both longitudinal and circular muscles
most have chaetae [setae] (chitonous bristles secreted by the epidermis) that aid in locomotion and burrowing
Skeletal System
fluid in coelom acts as a hydrostatic skeleton

11. Annelid Characteristics
Gas exchange
mainly by diffusion
Class Polychaeta often has specialized structures for gas exchange
(e.g. parapodia, gills)

12. Annelid Characteristics
Digestive System
complete
regional specialization

14. Annelid Characteristics
Circulatory System
closed circulatory system composed of blood vessels (some of which are contractile and act as “hearts”)
some circulation is also accomplished by the coelomic fluid

15. Annelid Characteristics
Excretion
excretion is accomplished by organs called nephridia (singular nephridium)
predominantly sexual
Reproduction

16. Phylum Annelida
Class Polychaeta
Class: Clitellata
Subclass: Oligochaeta
Subclass: Hirudinea

17. Class Polychaeta
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18. Class Polychaeta
most marine; about 30 species that are freshwater and brackish water in the US.
this class contains 2/3 of all known Annelids
have a well developed head with specialized sense organs
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19. Class Polychaeta
have many chaetae [setae] (chitonous bristles secreted by the epidermis)
(Poly = many, chaeta= setae)
these setae are arranged in bundles on paddle-like appendages called parapodia
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setae

20. Class Polychaeta
Parapodium
chaetae
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The parapodia function in gas exchange, locomotion, and feeding.

21. Parapodia are biramous

22. Class Polychaeta Tagmatization (tagmosis)
the fusion and specialization of formerly metameric segments
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23. Class Polychaeta Many are filter-feeders with specialized structures
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24. Terebellids with tentacles that creep over the surface of the substratum and accumulate food

25. Class Polychaeta Many are predatory with specialized structures: Jaws
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26. Class Polychaeta
Many construct their own homes out of CaCO3 or sand debris and mucous
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27. Class Polychaeta Reproduction usually dioecious
no permanent sex organs; gametes are shed into coelom
fertilization is usually external
indirect development  trocophore larvae
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28. Class Polychaeta Epitoky this swarming behavior is usually
In some species, the rear portion of the worm (“epitoke”: carries the eggs or sperm), breaks off from the body and swims to the surface to reproduce. The remaining benthic worm (“atoke”) continues to feed and grow and will eventually produce new epitokes.
To synchronize these spawnings,
this swarming behavior is usually
triggered by the full moon.
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29. Polychaetes Swarming

30. Polychaetes Swarming

31. Class Polychaeta Reproduction asexual Epitokes
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Epitokes

32. Symbiotic relationships
Many scaleworms are found near, or in the mouth, of brittlestars, starfish, sea urchins, and molluscs.
The scaleworm eats its host’s leftovers and with its vicious jaws, it will attack any predator trying to eat it’s host.
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33. Subclass Oligochaeta
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34. Subclass Oligochaeta terrestrial, freshwater and few marine
have few setae (Oligo = few, chaeta = setae)
usually feed on detritus
(decaying organic matter)
have specialized digestive system to obtain the maximum amount of nutrients out of the detritus (e.g. typhlosole, gizzard, crop…)

35. Subclass Oligochaeta typhlosole-
infolding of the dorsal side of the intestine
increases surface area for absorption of nutrients
typhlosole
gut

36. Subclass Oligochaeta Reproduction usually monoecious
cross-fertilize by
exchanging sperm
clitellum
testis

39. Earthworms Secret Cocoons Where They Store Their Eggs!

40. Ecology
Earthworms are essential soil aerators in terrestrial and aquatic habitats
If all the material ever moved through earthworms was piled up, the heap would rise 30 miles , more than 5 times the height of Mount Everest!!
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41. What is the most exciting thing about earthworms?

43. What is the most exciting thing about earthworms?
The Giant Gippsland earthworm, Megascolides australis can reach lengths of nearly 4 meters, the Central and South American Glossoscolecidae can reach 2 meters and the Australian earthworm Terriswalkeris terraereginae can get to 2 meters in length and the mucin it releases is luminescent!

44. What is the most exciting thing about earthworms?
The Microchaetus rappi more commonly know as the Giant South African Earthworm to over 20 feet long!