Annelids Chapter 35 B

About Annelids The term annelida means “little rings” The rings refer to the many body segments

Characteristics This is a phylum with 15,000 species All have bilateral symmetry Like mollusks – they are coelomates

Characteristics Segmentation is their most distinguishing feature Each segment has its own coelom Allows different body parts to expand or contract independently Provides an insurance policy against injury

Characteristics More distinguishing features: Setae (external bristles) Parapodia ( fleshy protrusions)

Class Oligochaeta “Few Bristles”

Oligochaeta These annelids live in freshwater or in the soil They do not have parapodia They have very few setae ( “few bristles” )

Oligochaeta These annelids have more than 100 segments Circular and longitudinal muscles line the body

Oligochaeta – digestive system Earthworms ingest soil as they pass through it Soil enters the pharynx to the esophagus

Oligochaeta Then from the esophagus to the crop Temporary storage site From the crop it moves to the gizzard Mechanical break down using stones

Oligochaeta From the gizzard to the intestine Nutrients absorbed Waste proceeds through to the anus

Oligochaeta – circulatory system Annelids have a closed circulatory system The system contains 5 pairs of aortic arches The arches link the dorsal to ventral blood flow

Oligochaeta – respiratory system Mucus and a cuticle keep Annelids moist They absorb O2 and CO2 directly thru the skin

Oligochaeta – excretory system Annelids get rid of waste and excess water with excretory tubules called nephridia Each segment – except first three and last – have their own pair of nephridia

Oligochaeta – nervous system The nervous system is a chain of ganglia Ganglia connected to a ventral nerve cord Branches carry impulses to each segment

Oligochaeta – reproduction Earthworms are hermaphrodites They are held together by setae and a film of mucus – during reproduction

Oligochaeta – reproduction Their clitellum secretes the film of mucus The clitellum is a thickened section on the body of an earthworm

Class Polychaeta “Many Bristles”

About Polychaeta About two-thirds of all Annelids are here They have antennae They have specialized mouth parts Most live in a marine environment They are free-swimming predators

Class Hirudinea

About Hirudinea This is the smallest class of Annelids These are the leeches Most live in calm waters

About Hirudinea They have no setae or parapodia They have anterior and posterior suckers

Annelids Chapter 35 B The End