Download Platyhelminthes - cynthiablairlhs

Platyhelminthes
• General characteristics:
– Known as “flat worms.”
– Body plan: acoelomate,
incomplete digestive tract, and
bilateral symmetry
• Habitat: free living in aquatic
environments, parasitic in
host’s bodies
Platyhelminthes
• Nutrition:
• Parasitic - (blood, tissue, or
predigested materials from
host’s intestines) OR
• Scavengers and Saprobesfeed on small living or dead
organisms
• Feeding:
Platyhelminthes
• Planarians-capture food by
wrapping itself around prey,
entangling in it slime and
pinning it down, then they
extend pharynx from mouth
to eat.
• Parasites have specialized
mouth parts, hooks and
suckers 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
– Parasitic have no need for digestion,
they absorb nutrients already broken
down by host
• Excretion: diffusion through the
body wall
– planarians have flame cells to excrete
water and wastes through pores, and
regulate osmosis.
– Waste can also exit through the mouth
Platyhelminthes
• Respiration and Circulation: Diffusion of gases through the
skin, skin must remain moist
Platyhelminthes
• Nervous: most have ladder
like system, with ganglia
(mass of nervous tissue)
functioning as a brain,
eyespots, sensory lobes and
respond to touch and
chemicals
– Demonstrates cephalization,
nervous tissue is concentrated
in the head region.
• Not used as much in parasitic
forms, due to lack of predation.
Platyhelminthes
• Reproduction:
– Sexual Reproduction:
• Hermaphrodites
• Parasitic worms require
hosts to reproduce
– Secondary host
contains larval stages
– Primary host is infected
with sexually mature
• 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
Platyhelminthes
• Reproduction:
– Asexual reproduction through
fragmentation or fission.
Platyhelminthes
• Mobility:
– Cilia for gliding
– Muscle cells
controlled by
nervous system to
react to stimuli
• Three muscle layers:
outer circular, inner
longitudinal and a
diagonal
– May also secrete
mucus to move
along.
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-most common in
US. (live in large intestine)
– Guinea worms
– Trichinella (spread by eating
raw pork with encysted
larvae)
– Filarial worms are known to
cause heart worms in dogs
and is also know to cause
Elephantiasis
Annelida
• General characteristics:
– Known as “segmented
worms”
– Coelomates, well
developed coelom.
• Habitat: aquatic and
moist soil
– Approximately 2/3rds of
all annelids are marine
polychaetes
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)
– The dorsal blood vessel pumps red blood
anteriorly; 5 pairs of hearts (aortic arches) pump
blood to a ventral vessel
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, displays great
cephalization with
developed eyes, jaws and
other sense organs
– 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
• Reproduction
Annelida
– Most sexually
– Some use external fertilization
and have separate sexes
– Earth worms and leeches are
hermaphroditic, but rarely
fertilize their own eggs
– To mate they align parallel and
facing opposite directions to
exchange sperm, the clitellum
secretes mucus that forms a
slime tube to prevent the eggs
and sperm from drying out.
– There is no larval stage.
– Only during breeding season do
the polychaetes have
reproductive organs.
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