1. Phylum Annelida

4. Phylum Annelida From the Latin Annellus a “little ring”.
Segmented body
Metamere – segment in the body
Setae
Small hair-like structures
Absent in leeches
Coelom divided by septa
Separating tissue 4

5. Phylum Annelida
The segments of an annelids body are separated by internal walls called septa.
Most of these segments are the same but a few are modified to perform special functions such a photoreceptors, antennae, etc. 5

6. Metamerism
Septa
Pygidium
Prostomium
Peristomium

7. Phylum Annelida
Annelids range in size from the Giant Earthworms, of which Michrochaetus rappi (Michrochaetus michrochaetus) is the largest
average length of 1.36 m (54 ins) and a record breaking specimen has been recorded that measured 6.7 metres (22 ft) in length, it was 2cm (0.8 ins) in diametre.
The smallest Annelid known to science is Chaetogaster annandalai
full grown at 0.5 mm (0.02 ins).

8. General Annelid Anatomy

9. Body Plan Cylindrical Bilateral symmetry True coelom
Annelids are the first major phyla showing segmentation (metamerism) which is advantageous to movement, safety, and tagmatization

10. Feeding Annelids have a complete digestive system
The digestive tract is a long tube from the mouth to the anus.
Their system contains mouth, pharynx, esophagus, crop, gizzard, intestine and anus
They have a pharynx which is used to grind up the larger particles of food. 10

11. Feeding Some annelids are carnivorous.
Carnivorous annelids can extend the pharynx through the mouth. These have two or more sharp jaws attached to it which are used to catch its prey.
In earthworms the pharynx acts like a pump pulling in soil and detritus through the mouth and forcing it into the gut.
In parasitic annelids the pharynx is used to suck blood from the host.
Some aquatic annelids are filter feeders and use fan-like structures to catch food particles.

12. Respiration Aquatic annelids breathe through gills.
Many annelids take in oxygen and give off carbon dioxide through their skin. The skin must stay moist for this type of gas exchange to occur.
Terrestrial annelids secrete a thin protective coat called a cuticle to hold moisture around them. 12

13. Circulatory System
Annelids usually have a closed circulatory system with two blood vessels running the length of the body.
In earthworms there are several ring vessels connected to these blood vessels in the anterior part of the worm.
The ring vessels are muscular and contract in rhythm so they are sometimes referred to as hearts. They do help pump blood through the system. In other annelids the blood is moved around by the worms movements. 13

14. Closed Circulatory System14

15. Excretion
Solid waste is removed through the anus while waste resulting from cellular activity is removed by a pair of nephridia in each segment of the body. 15

16. Nervous System Annelids have a well developed nervous system.
Sense organs are most developed in the free-living marine annelids. They often have sensory tentacles, photoreceptors, two or more eyes, and statocysts. 16

17. Nervous System cont’d
A statocyst is an organ used to detect gravity while they are in the water.
Many other annelids have simpler sensory systems like the earthworm. They rely only on cells in their skin to sense their environment. 17

18. Nervous System
Fig 18 18

19. Movement
Annelids have two major groups of muscles they use to move. Longitudinal muscles run from the front to the rear. These make the worm shorter when they are contracted.
The other group runs in circles around the worm. When they are contracted they make the worm skinnier. These two muscle groups are used together to help the worm wiggle forward. 19

20. Movement

21. Setae – help in movement

22. Reproduction
Most annelids reproduce sexually but a few can reproduce by budding.
Oligochaetes are hermaphroditic and during copulation they line up facing in the opposite direction
The clitellum secretes a mucous that holds the worms in place
Later, the clitellum acts as a cocoon where the fertilized egg develops 22

23. Earthworm Reproduction23

24. Palolo worm spawning.

25. Trochophore larva
Apical tuft
Stomach
Ciliary band
Mouth
Anus

26. Annelid development

27. Classification Class Polychaeta (many hairs)
Class Oligochaeta (few hairs)
Class Hirudinae (leeches)

28. Class Polychaeta Many setae Parapodia = “paired feet”
Characterized by paired paddle-like appendages on the segments.
The appendages are tipped with bristles that help the move about.
They live in the ocean, usually around reefs. 28

29. Fig. 17.3 29 29

30. Class Polychaeta
Parapodium
Head
Tentacle 30

31. Polychaete Worm Predatory Jaw Tentacle Everted pharynx Palp Eye Cirrus
Parapodium 31 31

32. Nereis 32

33. Class Polychaeta Fireworm33

34. Sedentary Polychaete Lugworm
Fig. 17.5 34 34

35. Fig. 17.4 35 35

36. 36

37. Pelagic* Polychaete
*Drift in the open ocean 37

38. 38

39. 39

40. 40

41. Class Oligochaeta Few setae
have bristles but they are much shorter and help the earthworm burrow through the soil.
Clitellum
No parapodia
Monoecious
Both male and female parts 41

42. Earthworms play an important role in soil fertility
Return nutrients to soil by decomposing dead leaves and organic matter
Burrowing allows air and water to penetrate to roots
Tunnels loosen soil so roots can grow more easily
“intestines of the earth”
-Aristotle 42

43. Lumbricus terrestris - earthworm
Enrich soil
Exceedingly important in soil creation, particularly in temperate areas.
Without them, agriculture and perhaps the whole of human society as we know it would never have evolved. 43

44. External Structures of an Earthworm
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
External Structures of an Earthworm

45. The Anatomy of an Earthworm
Section 27-3
Anus
Clitellum
Circular muscle
Longitudinal muscle
Nephridia
Ganglia
Ring vessels
Reproductive organs
Ventral blood vessel
Ganglion
Brain
Mouth
Dorsal blood vessel
Crop
Gizzard
Body segments
Setae

46. Fig c

47. Body wall
Epithelium
Circular muscle
Longitudinal muscle

48. Class Hirudinea - Leeches
No setae
Anterior & posterior sucker
Most live in fresh water
Feed
Invertebrates
Body fluids
Blood

49. Class Hirudinea
Usually no more than 6 cm in length but some tropical species can reach 30 cm.
After they attach to a host they release a substance called hirudin into the wound. This keeps the blood from clotting.
A leech can take in up to 10 times its weight in blood during a single feeding. 49

50. 50

51. 51

52. 52

53. 53

54. Fig

55. PARASITIC SEGMENTED WORMS LEECHES
Medical uses

56. Man vs. Wild - Leeches

57. Annelid
Annelid 3
Annelid 4

58. Dirty Jobs worm grunting

59. Dirty Jobs – Bloodworms

60. Video! Annelida (Leech Therapy)
Caution! If you don’t like leeches, you won’t like this news clip.
Copyright © 2010 Ryan P. Murphy

61. Video Link! Leeches NOVA podcast