Download Characteristics of Annelids

Biology 2 Chapter 35: Mollusks and Annelids
Section 2 Notes: Annelida
Characteristics of Annelids
1. The phylum Annelida is made up of bilaterally symmetrical, segmented worms.
2. This phylum includes common earthworms, feather-duster worms, and bloodsucking
leeches.
3. They are called annelids, which means “little rings” and refers to the many body
segments.
4. Annelids have a true coelom that is divided into separate compartments by partitions.
5. Most annelids have external bristles called setae (singular, seta), and some have fleshy
protrusions called parapodia (singular, parapodium).
Class Oligochaeta
6. Annelids of the class Oligochaeta generally live in the soil or in fresh water and have no
parapodia.
7. Oligochaeta means “few bristles”; these annelids have a few setae on each segment.
8. The most familiar member is the earthworm.
Structure and Movement
9. An earthworm’s body has over 100 nearly-identical segments.
10. Circular and longitudinal muscles line the interior body wall.
11. Locomotion is made possible by segmentation.
Feeding and Digestion
12. Earthworms ingest soil as they burrow through it.
13. Soil is moved through these structures:
Mouth
Pharynx
Esophagus
Crop
Gizzard
Intestine includes the typhlosole
Anus
14. Earthworms play an important role in the condition of soil.
Circulation
15. Contractions of the aortic arches and the dorsal blood vessel force blood through the
closed circulatory system.
Respiration and Excretion
16. Oxygen and carbon dioxide diffuse through the skin, which contains many small blood
vessels and must be kept moist.
17. Cellular wastes and excess water are excreted through nephridia.
Neural Control
18. The nervous system of an earthworm consists of a chain of ganglia connected by a
ventral nerve cord.
19. Sensory structures are found in all segments but are concentrated at the anterior end.
Reproduction
20. Earthworms are hermaphrodites, but an individual worm cannot fertilize its own eggs.
21. During mating, earthworms press their ventral surfaces together.
22. They are held together by their setae and by a film of mucus secreted by each worm’s
clitellum.
23. The sperm from each worm move through the mucus to the seminal receptacle of the
other.
24. The clitellum secretes a tube of mucus and chitin.
25. Fertilization occurs inside the tube, which forms a protective case for the young worms.
Class Polychaeta and Class Hirudinea
26. Most annelids are members of the class Polychaeta, which means “many bristles.”
27. Polychaetes differ from other annelids in that they have antennae and specialized
mouthparts.
28. They are the only annelids that have a trochophore stage.
29. Hirudinea is the smallest class of annelids, consisting of about 500 species of leeches.
30. Leeches have no setae or parapodia.
31. Many leeches are carnivores but some are parasites that suck blood from other animals.