Segmented Worms Section 27.2

Animal Classification Sponges Cnidarians Worms Mollusks Arthropods Enchinoderms - Phylum Platyhelimenthes - Phylum Nematoda - Phylum Annelida Worms Invertebrates Animals Fishes Amphibians Reptiles Ectotherms (cold-blooded) Vertebrates Birds Mammals Endotherms (warm-blooded)

Segmented Worms Phylum Annelida Coelomates with two body openings 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 Bristleworm Leech

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