WORMS
Flatworms: Phylum
Platyhelminthes






Soft and Flat
Tissues and Internal Organ Systems
3 embryonic germ layers (Ecto, Meso, &
Endoderm)
Bilateral symmetry
Cephalization
Acoelomates-without coelom (no fluidfilled body cavity)
Feeding
•Carnivore
•Scavenger
•Parasitic



Mouth/anus with pharynx (muscular tube that
moves food and waste)
Gastrovascular cavity – digestion/absorption
Parasites – simple or no digestive system b/c
feed on blood, tissue fluids, or cell pieces of host
Respiration, Circulation,
Excretion


Diffusion (transport O2 and nutrients)
through body walls
Flame cells – remove excess water and
waste

Connected to pores in the skin
Response



Ganglia – controls N.S. (nerve cell cluster)
Eyespot – detects light changes
Some have specialized cells to detect
chemicals, food, etc.
Movement


Cilia on epidermal
cells for gliding
Muscle cells for
twisting/turning
Reproduction




Hermaphrodites
Sexual by 2 worms
joining, exchanging
sperm, and each lay
eggs
Internal fertilization
Asexual by fission
(organism splits in 2
and each half grows
new parts)

Figure 27–3 The Anatomy of a Flatworm
Ganglia
Eyespot
Head
Nerve
cords
Gastrovascular
cavity
Flatworms use a pharynx to suck
food into the gastrovascular
cavity. Digested food diffuses
from the cavity into other cells of
the body. Eyespots in some
species detect light.
Mouth
Excretory
system
Freshwater flatworms have
simple ganglia and nerve
cords that run the length of
the body. The excretory
system consists of a network
of tubules connected to flame
cells that remove excess
water and cell wastes.
Ovary
Testes
Pharynx
Flame cell
Excretory
tubule
Most flatworms are
hermaphrodites, having male
reproductive organs (testes)
and female reproductive
organs (ovaries) in the same
organism.



Classes of Flatworms:
Turbellarians
Flukes
Tapeworms
Class Turbellaria:
Turbellarians



Free-living
Marine or fresh water
Not Parasitic
Ex. Pseudobiceros gloriosus
Tropical free-living flatworm (non-parasitic)
Ex. Planaria
Cross-eyed; fresh water free-living flatworm
(non-parasitic)
Class Trematoda: Flukes




Parasitic
Infect internal organs of
hosts
Blood flukes – travel to
intestines of host
Some have Multiple
Hosts
Ex. Blood Fluke (not free-living)
Parasite that
matures in human
blood vessels
Schistosoma mansoni
(has multiple hosts:
Snail=intermediate host
Human=primary host)
Figure 27-5
Primary host
(human)
Intermediate host
(snail)
Human
Adult
intestine
fluke
Flukes mature and reproduce
sexually in the blood vessels of
human intestines. Embryos are
released and passed out with
feces.
Embryo
After asexual
reproduction, new
larvae are released
from the snail into the
water. They then infect
humans, the primary
host, by boring through
their skin.
Tailed
Ciliated
larva
larva
Once in the water,
embryos develop into
swimming larvae that
infect an intermediate
host (snail).
Class Cestoda: Tapeworms





Parasitic
Lives in intestines
Long and flat
Scolex-head with
suckers or hooks
Proglottids-body
segments
• Cow/Fish
(intermediate host)
consumes food or
water w/ zygotes.
• Hatch to larvae and
burrow into muscles
as cysts (protected)
•human eats meat not
fully cooked and
larvae activated to
grow to adult in
human intestines.
Roundworms: Phylum Nematoda




Unsegmented
Most are free-living
Digestive tract with
two openings – mouth
and anus
Pseudocoelom-false
body cavity
Feeding


Most are carnivores
Use mouth parts and
spines to catch food
Hook Worms
Respiration, Circulation,
Excretion

Diffusion through body walls
Response



Simple nervous system
Nerves run body length from Ganglia in
head
Simple sense organs to detect chemicals
from prey or hosts
Movement


Hydrostatic skeleton
Muscles and fluid in the pseudocoelom
work together to produce movement
Reproduction



Sexual
Internal fertilization
Separate genders
Human Disease
--Parasitic Roundworms




Trichinosis-Causing Worms
Filarial Worms
Ascarid Worms
Hookworms
Trichinella  Trichinosis



Cysts are ingested from
eating animal muscle
tissue
Females burrow into
intestinal wall
Larvae travel to organs
via bloodstream and form
cysts
Filarial Worms




Live in blood and
lymph vessels
Transmitted by
mosquitoes
Can block the
movement of fluids
Elephantiasis
Ascaris
1. Eggs hatch in intestines
2. Larvae burrow into
bloodstream to lungs
3. Travel to air passages,
then swallowed
4. Carried to the intestines
and mature
5. Eggs released via feces
• Spread by eating
improperly washed
vegetables (foods)
Hookworms






¼ of the human population infected with
hookworms
Eggs hatch outside body and develop in soil
Use sharp toothlike plates and hooks to burrow
into skin and enter bloodstream
Travel to lungs and then intestines
Suck blood causing weakness
Don’t walk barefoot outside!!!
Annelids: Phylum Annelida
--Segmented worms with a
coelom (body cavity) that is
lined with mesoderm
Feeding and digestion


Filter feeders to predators
Earthworm
Full Digestive Tract: mouth  pharynx 
esophagus  crop  gizzard  intestine 
anus
 Crop- store food
 Gizzard- grind food

Circulation

Closed system, 2 major blood vessels
Dorsal blood vessel: tail  head (pumps like
heart)
 Ventral blood vessel: head  tail

Respiration and Excretion

RespirationSkin (moist due to mucus secretion) - land
 Gills - aquatic


ExcretionNephridia - filter out fluid/liquid waste
 Anus – solid waste


Movement
Hydrostatic skeleton
Longitudinal muscles – short and fat
 Circular muscles – long and thin



Setae- brush hair-like projections
ReproductionMostly sexual, some hermaphrodites, some
separate sexes
 Clitellum-thick band secretes mucus ring after
2 worms exchange sperm for fertilization
 Mucus ring slips off and forms protective
cocoonhatching

Classes of Annelids
Class Oligochaeta:
Oligochaetes- Earthworms


Few setae on each segment
Soil or fresh water
Class Hirudinea: Leeches



External parasites
Suck blood and body fluids of host
Medicinal Uses

Reduces swelling and prevents clotting
Class Polychaeta: Polychaetes




Sandworms,
bloodworms
Marine
Paired paddle-like
appendages w/ setae
Live in coral reefs,
sand, mud
What do you think caused this marking?





Worm?
Bacteria?
Virus?
Fungus?
Hickey?
Ringworm





Not caused by a worm!
Fungal infection
Can occur on any part of body
Contact with infected people, animals, soil,
etc.
Medically called Tinea
Earthworm Dissection
External View
Internal Structure
Pharynx
Aortic Arches
Seminal Vesicle
Seminal Receptacle
Septum
Crop
Gizzard
Intestine
Ventral Nerve Cord
Dorsal Blood Vessel