Flatworms
and
Annelids
Levels of Organization
• All animals are multicellular – made of more
than 1 cell
• Animals can be organized on the cellular,
tissue, or organ level of organization.
• Cell – Sponge
• Tissue – Jellyfish
- Have endoderm & ectoderm only
• Organ – Worms
- Have ectoderm, endoderm, and
mesoderm
Type of Body Plan
• Two body plans are present in the animal
kingdom:
• Sac plan:
• Incomplete digestive system with only one
opening.
• Ex: Jellyfish
• & planaria
•Tube-within-a-tube plan:
•Complete digestive system.
•Two openings allows for specialization
along the length of the tube.
•Ex: Roundworms, earthworms, insects
Type of Symmetry
• Three types:
• Asymmetrical animals have no particular
symmetry.
• Radial symmetry means the animal is
organized similar to a wheel.
• Bilateral symmetry means the animal has
definite right and left halves.
Type of Coelom
• Coelom - an internal body cavity where internal
organs are found.
• Ex: Mollusks, annelids, echinoderms,
vertebrates
• Pseudocoelom - a body cavity incompletely
lined with mesoderm.
• Ex: Roundworms, rotifers
• Acoelomates - have mesoderm but no body
cavity.
• Ex: Flatworms, sponges, jellyfish
Segmentation
• Segmentation is the repetition of body parts
along the length of the body.
• Animals can be segmented or nonsegmented.
• Segmentation leads to specialization of parts.
• Ex: annelids, arthropods, and chordates
(includes vertebrates).
Phylum Platyhelminthes
•Meaning – flatworms
•Symmetry - bilateral
•Sac body plan
•Non-segmented
•Acoelomates
•Organization – organ level
•Have organs for all life processes except
respiration and circulation
•Habitat – fresh or salt water, moist environments,
inside host
•Examples:
Tapeworms
Marine flatworms
Flukes
Freshwater planarians
Planarians • Lifestyle - free-living
• Habitat - freshwater
• Movement – secrete slime, push through with
cilia, muscles
• Excretion – flame cells – interconnecting canals
throughout body
• Response - small brain
- ladder of nerves
- light-sensitive eyespots
- Auricles sensitive to chemicals
• Respiration - diffusion
•Internal transport - diffusion
•Diet – plankton (small worms or crustaceans)
•Feeding – wrap around prey
- secrete slime
- extend pharynx to suck up food
•Digestion – occurs in GVC
•Gender - hermaphrodites
•Sexual reproduction – have sex, exchange sperm,
each planaria gets pregnant - 2 sets of young hatch
from eggs 2-3 weeks later.
•Asexual reproduction – capable of regeneration;
1 worm can even grow 2 heads or 2 tails!!
Planarian
Eyespot
Brain
Auricle
Longitudinal
nerve cord
Transverse
nerve cord
GVC
Pharynx
Flame
cells
Excretory pore
Mouth
Mesoderm
Endoderm
Ectoderm
GVC
Flame
cells
Cilia
Parasitic Flatworms
• Two classes - flukes and tapeworms
• Require host to carry on life cycle – see next slide
• Primary host – infect as adult
• Secondary host – infect as larval stage
• Tapeworm –
• Scolex with hooks and suckers to hold itself
inside the gut.
• No digestive system; absorbs host’s digested
food through skin
•Body is an assembly line of square sections
called proglottids, which contain male and
female sex organs.
•As proglottids mature, they break off, pass
with feces, and release eggs.
•When animals feed in feces-contaminated
food, larva eventually form cysts in muscles of
secondary host.
•When humans eat infected meat, larva hatch
from cyst, attach to intestine, and grow to
adulthood.
1. Hooks
2. Suckers
3. Scolex
4. Neck
5. Proglottids
6. Testes
7. Ovary
8. Eggs
9. Detached proglottid
10. Longitudinal nerve cord
11. Brain (ganglia)
12. Transverse nerve cord
Life cycle:
•Contracted by eating undercooked, infected
beef, pork, or fish.
•Transmitted to cats & dogs by fleas that have
eaten feces of infected host
•Primary symptom – weight loss
•In prolonged infections – worms migrate to
eyes, heart, brain, lungs, & liver & form cysts –
cause swelling, cramps, diarrhea, anemia, &
seizures
•Diagnosed by fecal exam; treated with medicine
Fluke
•Have sucker at anterior end to attach to host
•Various species – can infect digestive tract, bile
duct, blood, & lungs.
•Blood flukes cause schistosomiasis – one of the
most common worm infections worldwide
(about 200 million in mostly Middle East, Asia,
Africa, & S. America)
•Common in areas with poor sewage treatment
•Enter through skin when in infected water – see
life cycle diagram next slide
Schistosomiasis
•Diagosed by fecal exam; treated with
medicine
•Symptoms: nausea, abdominal pain,
increased bowel movements, diarrhea, weight
loss, fatigue
•Burrow through host, feed on host’s blood &
tissues.
•Can live for up to 2-3 decades inside host
(usually only 5-10 years)
•Reproduce non-stop – 100 – 300 eggs/day
Phylum Annelida (segmented worms)
• Symmetry - bilateral
• Organization - 3 germ layers – organ level
• Coelomates -have a body cavity – more
complex organs
• Segmented
• Habitat – fresh or salt water, soil
• Tube-within-a-tube body plan – specialized
organs in digestive tract (see earthworm later)
• Support - hydrostatic skeleton (fluid-filled
chambers in body).
• Respiration - breathe through their skin diffusion.
• Internal transport - closed circulatory system
with 5 aortic arches (hearts) and blood vessels
that run the length of the body and branch to
every segment.
• Excretion –
– Nephridia (tiny tubes found in each segment) remove
nitrogen waste through openings in body wall
– Anus removes waste from digested food.
•Movement - alternating contraction of
longitudinal and circular muscles found in each
segment.
•Response - brain connected to a ventral nerve
cord .
•Three classes –
•Polychaeta – marine worms
•Oligochaeta – earthworms
•Hirudinea - leeches
Earthworm, Lumbricus
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
Mouth
Pharynx
Esophagus
Crop
Gizzard
Intestine
Anus
Aortic arches (hearts)
Dorsal blood vessel
Ventral blood vessel
Brain
Ventral nerve cord
Clitellum
Setae
Clitellum
Testis
Sperm reservoir
Seminal
Ovary receptacle
Excretory pore
Nephridium
Tubule
H. Intestine
I. Coelom
J. Muscle
K. Muscle
L. Epidermis
L1. Cuticle
M1. Blood vessel
M2. Blood vessel
N. Nerve cord
O. Nephridium
P. Setae
Earthworms
• Have pairs of setae in each segment; when
muscles contract in each segment, setae anchor
in the soil, and aid locomotion.
• Diet - leaves & decaying matter
• Digestion: Mouth  Pharynx (swallows food)
 Esophagus (connects pharynx & crop) 
Crop (stores food)  Gizzard (grinds food –
contains small stones swallowed by the worm)
 Intestine (digests food)
•Gender - hermaphroditic.
•Reproduction
•Meet at clitellum (smooth part of worm),
which secretes a ring of mucus
•Each injects sperm into mucus
•Tube slides forward, picking up eggs
•Tube slides off body & is left behind
•Fertilization occurs within tube
•Worms hatch in a few weeks – no larval
stage
•Two sets of young
Leeches
• Most in fresh water, some in soil or salt water.
• 2 suckers (1 small anterior, 1 large posterior) to feed.
• Some are free-living predators; most are fluid
feeders that attach themselves to open wounds.
• Bloodsuckers cut through tissue with 3 saw-like
jaws – leaves “Y” – shaped wound.
• Anesthetic in saliva prevents victim from feeling
attack and dilates blood vessels; anticoagulant
(hirudin) in their saliva keeps blood from clotting;
pouches in crop allows for storage of up to 5 times
their weight – long time between feedings.