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- parasitic
3. 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
Schistomiasis (blood fluke):
 disease that causes tissue damage,
bleeding, tissue decay and possible
death
 Lungs, intestine, bladder, & liver
 200 million people affected worldwide
Human- Primary host
Snail- Secondary or
Intermediate host
Animation!
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
Life Cycle:
 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
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
Life Cycle:
 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
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