Flatworms, Roundworms, & Segmented Worms

Phylum Platyhelminthes

• Flatworms• Flat and thin bodies• Bilateral symmetry • Most are parasitic

Phylum Platyhelminthes

• Flatworms include planarians, flukes, and tapeworms

• 20,000 species of flatworms

Miscellaneous Information- Flatworms

• Movement- use of moving bodies of water or damp soil, or larger animals transporting them

• Nutrition- parasitic; the flatworm will take in food through same opening it eliminates waste

• Circulatory system- Gastrovascular cavity with one opening

• Digestion and excretion occur through same opening• Reproduction- flatworm splits in two forming a new

flatworm

Tapeworms Information• Can get tapeworm

infection by ingestion of food or water contaminated with tapeworm eggs or larvae

• Can cause intestinal infections

• Symptoms- poor appetite, diarrhea, weakness, gastrointestinal discomfort

Phylum Nematoda

• Roundworms• Ex. Pinworms and

hookworms• 90,000 species of

nematodes• Bilateral Symmetry • Live in wet soil or water• Eat dead leaves and other

materials• Some eat insects that

destroy plant roots• Some destroy plant roots

Flatworm Head

• Head holds attachment hooks for host attachment

• 2 eyespots to help detect light

• Also contains brain called 2 simple brains called ganglia- simple bundles of nerves

Phylum Nematoda

• Some roundworms can live in humans and make them sick

• Roundworms have a complete digestive tract with 2 openings

Nervous System of Roundworms

• Two nerve cords that transmit impulses in the roundworm

Miscellaneous Information- Roundworms

• Reproduction- sexually, eggs deposited in soil after fertilization

• Bilateral symmetry• No formal respiration, circulation, skeletal

systems

Phylum Nematoda

Phylum Annelida

• Annelids are segmented worms• Bodies are divided into many sections or

segments• Live in moist soil, freshwater, or saltwater • 15,000+ species of annelids• Examples: earthworms and leeches

Phylum Annelida

• Earthworms– Have bristlelike Setae on each segment- helps in

movement– Tunnel through soil to eat small pieces of food– Tunnels will loosen the soil and allow air to enter

which helps plants to grow

Leeches and Us

• Used in medicinal treatment• Abscesses, painful joints, glaucoma,

myasthenia, and to heal venous diseases and thrombosis

Phylum Annelida

Miscellaneous Information- Segmented Worms

• Nervous system- ganglia nerve centers in each segment that are connected by nerve cords to brain

• Closed circulatory system- like humans • Gas exchange through skin- need for worm to live near

water • Digestion- complete internal digestive tract that runs

length of body– Gizzard- muscular sac and hard particles help grind soil and

food before they pass into intestine Nephridia- collect/remove waste from each segmentPg. 731 is a good reference for earthworm body

Miscellaneous Information- Segmented Worms

• Reproduction- Hermaphrodites• Produce both eggs and sperm

Phylum Annelida

• Leeches– Eat small invertebrates– Can attach to skin of vertebrates and feed on its

blood– Anesthetics in chemicals of bite to prevent pain– Leech secretes chemical so blood does not clot

Bilateral Symmetry and Body Plans

• All bilaterally symmetrical animals developed from 3 embryonic cell layers:– Ectoderm– Endoderm– Mesoderm

– 3 types- Acoelomates, Pseudocoelomates, Coelomates

Acoelomates

• Develop from the 3 layers but have no body cavities

• Digestive tract extends throughout body• May have been first group of animals to

evolve• Ex. Flatworms

Acoelomates

Pseudocoelomates

• Develop from the 3 layers• BUT also has a space that develops between

the endoderm and mesoderm- called a pseudocoelom (difference between flatworm and roundworm)

Pseudocoelomates

Coelomates

• Body cavities form from Coelom (fluid filled space that is completely surrounded by mesoderm where specialized organs and organ systems, serves to cushion and protect organs)

• Humans, insects, fishes• Example: Earthworm • Greatest diversity among animals

Coelomates

Earthworm

Compare and Contrast

• Flatworm and Earthworm digestive tracts • One opening to flatworm’s digestive tract (pharynx)• Earthworm’s digestive tract has 2 openings (mouth

and anus)

3 types of worms Segmented Worms Roundworms Flatworms

Phylum Annelida Phylum Nematoda Phylum Platyhelminthes

Segmented/sectioned bodies, bilateral symmetry

Bilateral symmetry Bilateral symmetry, flat and thin bodies

Moist soil, freshwater, or saltwater

Wet soil or water Parasitic- live inside a host or in water

Complete digestive tract- 2 openings (mouth and anus)

Complete digestive tract with 2 openings (mouth and anus)

One digestive opening (pharynx)

Coelomate- form from coelom (fluid filled space surrounded by mesoderm)

Pseudocoelomate- develop from 3 layers, with space between endoderm and mesoderm called Pseudocoelom

Acoelomate- develop from 3 layers but have no body cavities

Earthworms, leeches Pinworms, hookworms planarians, flukes and tapeworms