Flatworms, Roundworms, & Rotifers

Chapter 34

Phylum Platyhelminthes

Section 34.1

General Structure:

3 germ layers – ectoderm, mesoderm, and endoderm acoelomates

Bilateral symmetry Anterior and posterior ends

Dorsal and ventral surfaces only Flat body plan Flatworms!

General Functions:

Exchange oxygen and carbon dioxide directly with the environment to cells by diffusion No circulatory system or respiratory

system needed

Only one opening where food and wastes pass through!

Cephalization

Classification:

Four Classes:1. Turbellaria - non-parasitic

2. Trematoda- parasitic3. Monogenea - parasitic

4. Cestoda –parasitic

1. Class Turbellaria: 4,500 species Mostly marine Swim in wavelike

motion Glide over solid surfaces

on layer of mucus Example: Planarian

Dugesia freshwater

Video

Planarian Body Plan:

Planarian Organ Systems:

Digestive System: Scavengers & predators

Decaying plants & animal matter Prey on smaller organism

Pharynx – throat that extends to the middle of body video

Planarian Organ Systems:

Excretory System: Flame Cells – enclosed tufts of cilia that

draw excess water together and excretes it through pores video

Planarian Organ Systems:

Nervous System: Cerebral ganglia: two

clusters of nerve cells at anterior “Brain” Can learn

Eyespots: sense direction and intensity of light

Other senses: touch, water currents, chemicals

Planarian Organ Systems:

Reproductive System: Sexual:

Hermaphrodites Eggs laid in protective capsule

Hatch in 2-3 weeks

Asexual: Regeneration

2. Class Trematoda & 3. Class Monogenea:

Both are parasitic flukes Leaf-shaped flatworms

Endoparasites: Live in blood, intestines, lungs, liver, etc.

Ectoparasites: Live on external surfaces of aquatic

hosts

Structure of Flukes

Anterior & ventral suckers for attachment to host

Nervous system like planarian Except NO eyespots

Tegument – outer layer that protects from host’s immune and digestive system

Liver fluke

Reproduction of flukes: Most are hermaphroditic May release 10,000+ eggs at a time! Complicated life cycle (p. 692)

Life Cycle:

Primary host: adult parasite gets nourishment from this host Sexual reproduction

Intermediate host: larvae derive nourishment here Asexual reproduction

Fluke Diseases in Humans

Swimmer’s itch: minor skin irritation and swelling Small brown fluke in lakes (in Ohio) Dies within skin because humans are not

ideal hosts

Swimmer’s itch

disease that causes tissue damage, bleeding, tissue decay and possible death Lungs, intestine, bladder, & liver 200 million people affected worldwide

Human- Primary hostSnail- Secondary or

Intermediate host

Animation!

Schistomiasis (blood fluke):

WHO Info.

4. Class Cestoda 5,000 species of tapeworms Can live in intestines of most

vertebrates Enter through undercooked food with

eggs or larvae Symptoms of infection:

Digestive problems Weight loss Lack of energy anemia

Structure:

Tegument to protect from host Also absorbs nutrients from host

Scolex: knob-shaped organ with hooks and suckers to attach to host

Proglottids: body sections after a short neck Up to 2,000 per tapeworm!

Reproduction:

Hermaphrodites Each proglottid has ovaries and testes

Filled with 100,000+ eggs each! Eggs fertilized by sperm of different

proglottid

Life Cycle:

Cysts: dormant larvae surrounded by protective covering in animal muscle

Phylum Nematoda & Rotifera

Section 34.2

General Characteristics:

Bilateral symmetry Fluid filled body cavity

pseudocoelomate Holds internal organs Stores sperm & eggs Supports body Structure that muscles can contract

against

Phylum Nematoda Roundworms

Long, slender bodies that taper at both ends

1mm to 4ft Digestive tract with 2 openings

Anterior – mouth Posterior – anus One directional movement

Continued…

Most have separate sexes Cuticle – protective covering Free-living on land, salt and

freshwater 15,000 species known

150 species parasitic to plants and animals

Humans are host to 50 species!

Ascaris:

Roundworm parasite that lives in intestine Pigs, horses, & humans

Can totally block host’s intestine

Up to a foot in length Female produces 200,000

eggs/day

Eggs leave with feces and enter soil Enter humans with contaminated food and water

Larvae enter intestines and move to blood stream, then lungs, coughed up and swallowed back to intestines where they mate and reproduce

Life Cycle:

Hookworms:

Another intestinal parasite Mouth has cutting plates that clamp

onto intestine wall Feed on host’s blood which may lead to

anemia May cause slow mental and physical

development in children Affects 1 billion people in tropical and

subtropical regions

Hookworm

Enter host by boring through the feet

Eggs leave with feces Larvae develop in soil Enter host’s feet Hitch a ride with blood to the lungs Coughed up and swallowed to

intestines where adult develop

Life Cycle:

Trichinella: Infect humans and pigs

Adults embed in walls of intestine Larvae travel via blood to muscles Form cysts

Humans get it from eating undercooked pork

Causes disease trichinosis Muscle pain & stiffness Can cause death

Pinworm – most common in U.S. Live and mate in lower intestine Female crawls out at night and lays eggs

around anus Person scratches during sleep and

spreads eggs to everything touched Eggs ingested and hatch

Pinworm

Filarial worms – 250 million people infected in tropics Found in lymphatic system (collects

excess fluid from blood vessels) Can cause elephantiasis

Swollen limbs, skin hardens & thickens Can cause heartworm in dogs and cats Spread by mosquitoes

Phylum Rotifera Most are transparent (see-through)

Free-living in freshwater 100 to 50 micrometers

No water = dry up and look like grains of sand; when water is present again they go back to normal Cool adaptation!

Rotifer Structures: Cilia – sweep food into mouth Mastax – breaks down food Stomach Intestine – absorbs nutrients Cloaca – digestive, reproductive, and

excretory systems empty here Universal hole

Flame cells – pull excess water together

Anus – hole to the outside

Body Parts: video

Have cerebral ganglia and eyespots Reproduction by:

Parthenogenesis – unfertilized eggs become adult females