Platyhelminthes
• General characteristics:
– Known as “flat worms.”
– Body plan: acoelomate, bilateral
symmetry
• Habitat: aquatic or in host’s
body
Platyhelminthes
• Nutrition:
• Parasitic - (blood, tissue, or predigested materials
from host’s intestines) OR
• Scavengers and Saprobes
• Feeding:
Platyhelminthes
• Planarians extend pharynx
from mouth
• Parasites have specialized
mouth parts to attach to
their host.
Platyhelminthes
• Digestion:
– Extracellular: food is pumped
into digestive cavity or gut
and cells digest and absorb
nutrients, digested food is
then diffused into the other
body tissue
• Excretion: diffusion through
the body wall
– planarians have flame cells to
excrete water and wastes
through pores
Platyhelminthes
• Respiration and Circulation: Diffusion of gases through the
skin, skin must remain moist
Platyhelminthes
• Nervous: most have
ganglia (mass of
nervous tissue),
eyespots, sensory lobes
and respond to touch
and chemicals
– Demostrates
cephalization, nervous
tissue is concentrated in
the head region.
Platyhelminthes
• Reproduction:
– Sexual Reproduction:
• Hermaphrodites
• Parasitic worms require
hosts to reproduce
• Sexual reproduction
exchange sperm, internal
fertilization
Schistosome Life Cycle
Section 27-1
Flukes mature and reproduce
sexually in the blood vessels of
human intestines. Embryos are
released and passed out with
feces.
Primary host
(human)
Intermediate host
(snail)
Human
intestine
Adult
fluke
Embryo
Tailed
larva
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.
Ciliated
larva
Once in the water, embryos
develop into swimming larvae
that infect an intermediate host
(snail).
Shistosomiasis
Tapeworm Life Cycle
DON’T DO THIS!! GROSS!
Platyhelminthes
• Reproduction:
– Asexual reproduction through
fragmentation or fission.
Platyhelminthes
• Mobility:
– Cilia for gliding
– Muscle cells controlled by nervous system to react
to stimuli
The Anatomy of a Flatworm
Eyespot
Ganglia
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.
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
Mouth
Pharynx
Flame cell
Excretory
tubule
Most flatworms are
hermaphrodites, having male
reproductive organs (testes) and
female reproductive organs
(ovaries) in the same organism.
Platyhelminthes
• Common Examples:
– Turbellaria (Planarian)
– Trematoda (Fluke)
– Cestoda (Tapeworm)
Nematoda
• General characteristics:
– Known as “round worms”.
– Pseudocoleomate
– long and slender, tapered at both
ends
– protostomes
– bilateral symmetry
– Body is covered in a complex cuticle
Nematoda
• Habitat/Nutrition:
– Parasites
• Feeding
– Both mouth and anus connected by digestive tube
• Digestion: takes place in digestive cavity, digested food
diffuses into other body tissue.
– May also have digestive sacs that food is pumped into for
digestion.
Nematoda
Nematoda
• Circulation and Respiration: Diffusion of gases through the
skin
• Excretion: Canal system, diffusion through body wall or out
through mouth
• Nervous: simple nervous system, with a main ventral (belly)
nerve cord and smaller dorsal (back) nerve cord
Nematoda
•
Reproduction:
–
Sexual
–
–
–
–
usually dioescious
(separate sexes)
internal fertilization
genders differ in size,
shape and color
Parasitic worms require
host
Life Cycle of Hookworm
Life Cycle of Whipworm
Nematoda
• Mobility: Muscles along body wall for
movement
Nematoda
• Examples:
– Hookworms
– Pinworms
– Guinea worms
Annelida
• General characteristics:
– Known as “segmented worms”
– Coelomates
• Habitat: aquatic and moist
soil
Annelida
• Nutrition: heterotrophic, filter feeders,
parasites, scavengers, and saprobes
• Feeding: Pharynx used to obtain food
– Carnivorous species have two or more sharp jaws
Annelida
• Digestion: extracellular, takes
place in intestine
– Earthworm: pharynx →
esophagus→ crop (storage) →
gizzard (ground) → intestines
(absorption)
Annelida
• Excretion:
– Digestive wastes
pass out through the
anus
– Cellular wastes
containing nitrogen
is passed out by the
nephridia (simple
kidney)
Annelida
• Circulation:
– closed (blood contained in vessels)
Annelida
• Respiration:
– Aquatic: breathe
through gills
– Land dwellers: diffusion
through skin (must stay
moist) typically secrete
a mucus to keep skin
moist
Annelida
• Nervous:
– Best developed sense
organs in free living
marine organism
– Well developed nervous
systems consisting of
brain and spinal cord
– Two or more pairs of
eyes, sensory tentacles,
chemical receptors and
statocysts that help
detect gravity
Annelida
• Reproduction
– Most sexually
– Some use external
fertilization and
have separate sexes
– Earth worms and
leeches are
hermaphroditic, but
rarely fertilize their
own eggs
Annelida
• Mobility
– Two major groups of
muscles that function as
part of the hydrostatic
skeleton
– Longitudinal and circular
muscles, move by
alternating contractions
– Earthworms have hair-like
structures called setae
that allow them to easily
grip a surface.
– Marine worms have
parapodia to use for
swimming and crawling
Section 27-3
Anus
Setae
Body segments
Gizzard
Crop
Dorsal
blood vessel
Clitellum
Mouth
Brain
Circular muscle
Longitudinal
muscle
Nephridia Ganglia
Ring
vessels
Ganglion
Ventral
Reproductive blood vessel
organs
Annelida
• Examples:
– Earthworms
– Leeches
– Marine worms