Segmented Worms

Section 27.2

Animal Classification

Animals

Invertebrates

Vertebrates

SpongesCnidariansWormsMollusksArthropodsEnchinoderms

Ectotherms(cold-blooded)

Endotherms(warm-blooded)

FishesAmphibiansReptiles

BirdsMammals

Worms

- Phylum Platyhelimenthes- Phylum Nematoda- Phylum Annelida

Segmented Worms

Phylum Annelida Latin term anellus = “little ring" Examples: Earthworms, bristleworms, and

leeches Coelomates with two body openings

Segmented Worms

Can be found in most environments, except in frozen soil and dry, compact sand

15,000 species of segmented worms

Earthworm

Leech

Bristleworm

External Anatomy of an Earthworm Prostomium – a tongue-like lobe above the

mouth Clitellum - the swelling of the earthworm near

its anterior side Setae - Tiny bristles that help earthworms

and bristleworms move through soil Mouth Anus

Nervous System

Segmented worms have simple nervous systems

Some species have eyes and brains All species have nerve cords and ganglia

Internal view of an earthworm

Circulatory

Segmented worms have a closed circulatory system – blood flows through vessels to reach all parts of the body Open circulatory system – blood is not enclosed

in vessels throughout the entire body Examples: flatworms and roundworms

Internal view of an earthworm

Respiration

Segmented worms must live in water or wet areas because they are able to exchange gases directly through their moist skin

Digestion

Annelids have a complete digestive system Have a crop and a gizzard

Crop – a sac that holds soil temporarily before it moves into the gizzard

Gizzard – a muscular organ that grinds food

Internal view of an earthworm

Excretion

Annelids have two nephridia in almost every segment that collect waste products and transport them out of the body

Internal view of an earthworm

Reproduction

Earthworms and leeches are hermaphrodites During sexual reproduction, worms exchange

sperm Eggs are fertilized and laid in the soil The eggs hatch in 2-3 weeks Bristleworms have separate sexes and

reproduces sexually

Internal view of an earthworm

Leeches

Many species are parasites that suck blood or other body fluids from their hosts

Front and rear suckers enable leeches to attach themselves to their hosts

Leeches

The saliva contains chemicals that act as a anesthetic Example – Novocain

Other chemicals prevent the blood from clotting

Leeches are used medically to remove decaying tissues of patients

Leeches

A leech can ingest 2-5 times its own weight in one meal

A leech will drop off its host when its full and may not eat again for months