1. Chapter 37-2
Annelida

2. Phylum: Annelida Annelid: means “little rings” Can include
Many body segments
Can include
marine species
Earthworms
Leeches

3. Characteristics and Classification
Bilateral Symmetry
Coelomates
Segmented (important evolution)
Developed organ systems
External Bristles and Fleshy Protrusions
Setae #
Parapodia
Presence or absence
Determine which class division
Oligochaeta, Polychaeta, Hirudinea

4. Oligochaeta Live in soil or fresh water Have no parapodia
Look for adaptations for burrowing
Have no parapodia
Name means “few bristles”
Have few Setae
Most familiar member is the Earthworm

5. Oligochaeta – Structure and Movement
Earthworm body divided in more than 100 virtually identical segments
Locomotion method
Worm anchors some middle segments by setae
Contracts muscles in front of those segments
This increases pressure on coelomic fluid
Elongates the animal and pushes anterior end forward
Anterior setae then grip ground, pulling the posterior segments forward

6. Oligochaeta – Feeding and Digestion
Ingest soil as they burrow through
Sucked into mouth by the pharynx
Esophagus – crop – gizzard – intestine - anus
Play an important role to maintain soil fertility
Decomposition
Release nutrients
Oxygen penetration
Loosen soil

7. Oligochaeta – Circulation
Closed circulatory system
Blood travels to posterior end through ventral blood vessel
Blood returns to anterior end through dorsal vessel
Aortic arches link the two blood vessels at the anterior end

8. Oligochaeta – Respiration and Excretion
No specialized respiratory organs
Oxygen and CO2 diffuse directly through skin
Gas exchange only happens if skin is moist
Secrete mucus and have a thin cuticle
Eliminate cellular waste and excess water
Excretory tubules called nephridia
Each segment (except first 3 and last 1) contain a pair
Nephridia

9. Oligochaeta – Neural Control
Nervous system
Chain of ganglia connected by a ventral nerve cord
Most segments contain a single ganglion
Nerves branch from each ganglion
Several ganglia fused to form “brain” (cerebral ganglia)
Main function is to process simple info from sensory structures
Present in all segments, but concentrated at anterior

10. Oligochaeta – Reproduction
Hermaphrodites (Cannot self fertilize)
Mating: 2 worms press ventral surface together, anterior pointing in opposite directions
Held together by:
Setae & Mucus
Secreted by clitellum (thickened section)
Sperm moves through mucus to seminal receptacle

11. Oligochaeta – Reproduction Cont’d
The worms separate
After several weeks the clitellum secretes a tube
Made of mucus and chitin
Tube slide forward and picks up eggs and sperm
Fertilization occurs within tube
Young worm develops inside for 2-3 weeks before hatching

12. Polychaeta 2/3 of all annelids “many bristles” Mostly marine
Have antennae and specialized mouthparts

13. Hirudinea Smallest class, about 300 species Leeches Mostly freshwater
No setae or parapodia
Sucker at each end of body
Some are carnivores, but many are parasitic
Suck blood from host
Secrete anesthetic and anti-clotting substance