Sec. 27-3 Annelids

Phylum Annelida
segmented worms, true coelom
-Includes: earthworm, marine worms, leeches

Annelids

-Annelida means "little rings"
-body divided into segments separated by septum (Septum=internal wall)
- some have bristles called setae on each segment
-have closed circulatory system
-have well-developed nervous system with brain & nerve cords
-sexual reproduction, some are hermaphrodites

clitellum

*See Earthworm Labeling

Groups of Annelids

1. Class Oligochaeta - Earthworm
-Streamlined bodies for moving through soil
-Few setae, allows for gripping soil
-Live in soil or fresh water
-As earthworms pass food & soil through intestines, nutrients are absorbed and indigestible matter passes out through anus as castings
-Castings - enrich soil, earthworms aerate soil

earthworm

2. Class Hirudinea - Leeches
-external parasites with suckers on each end
- suck blood & body fluids from host
-most live in moist tropical habitats
-medicinal uses (circulation, anti-clotting)

3. Class Polychaeta - Marine worms
See p.698 fig.27-18
-includes:sandworms, bloodworms, & relatives
-have paired paddlelike appendages with setae

nereis