Transcript The Pseudocoelomate Body Plan: Aschelminthes

The Pseudocoelomate Body
Plan:
Aschelminthes
Chapter 11
Aschelminthes
• Seven different Phyla grouped
into either the
Lophotrochozoan (those that
do NOT molt)
or
Ecdysozoan (those that DO
molt)
Aschelminthes
Characteristics
–First animal to posses a body
cavity
– Pseudocoelom
•Distinct body cavity with no
peritoneal lining and
mesenteries.
•Visceral (internal) organs lie
free in the cavity
• A pseudocoelom
– Is a body cavity derived from the blastocoel, rather
than from mesoderm
Body covering
(from ectoderm)
Pseudocoelomates such as
nematodes have a body
cavity only partially lined by
tissue derived from
mesoderm.
Pseudocoelom
Digestive tract
(from ectoderm)
Muscle layer
(from
mesoderm)
Characteristics
Pseudocoelom – acts as an
internal hydrostatic skeleton
that functions
in
locomotion
Characteristics
• Most have a complete tubular
digestive tract (mouth-anus)
First time mechanical
breakdown of food, digestion,
absorption, and feces
formation
Characteristics
• Show eutely – same number of
cells for each animal and for each
given organ in all the animals of
the species
• Ex. Caenorhabditis elegans (a type
of nematode) has 959 cells
• Every worm in the species has 80
cells in their pharnyx
C. elegans
Nobel Prize (2002)
Brenner, Sulston and
Horvitz
– “Genetic regulation of
organ development and
programmed cell death”
Sydney Brenner
- C. elegans since 1963
http://www.nobel.se/medicine/laureates/2002/press.html
Characteristics
–Microscopic to meters in length
–Bilaterally symmetrical
–Unsegmented and cylindrical in
cross section
–Most are freshwater
–Osmoregulation through
protonephridia (mainly in
freshwater)
Characteristics
–Triploblastic
–Most are dioecious
– No separate gas exchanges
–Some cephalization is present
–Cuticle present – may bear
spines or scales and is useful
for protection and taxonomic
identification
Lophotrochozoan
Phylum Rotifera
(rota, wheel + fera, to bear)
Small animals 0.1-3 mm
Most abundant in
freshwater
About 1,000 cells (3
classes) and organs are
eutelic
Phylum Rotifera
• All have a Corona
(crown)- ciliated
organ for
locomotion and
food gathering
Phylum Rotifera
Posterior toes and
adhesive glands
called:
Pedal glandsecretions aid in
temporary
attachment of foot
to a substratum.
Feeding and Digestion
Feed on small microorganisms
and organic material
Coronal cilia brings food to
mouth
Food enters the Pharynx that
contains a muscular organ that
grinds food called Mastax
Feeding and Digestion
Then food passes through a
ciliated Esophagus to the
ciliated Stomach-complete
extracellular digestion and
absorption of food occurs.
Feeding and Digestion
Some species have ciliated
Intestine that becomes
Cloacal bladder- receives water
from the protonephridia, eggs
from ovaries, and digestive waste.
Cloacal bladder opens to the
outside via an Anus
Other Organ Systems
Protonephridia that empty into
the cloacal bladder function in
osmoregulation
Nervous System- 2 lateral
nerves and bilobed brain
Reproduction and Development
Some reproduce sexually
Many reproduce by
parthenogenesis- a type of
reproduction in which females
produce offspring from
unfertilized eggs
Reproduction and Development
Females
Germovitellarium- ovary and
vitellarium fuse
Males
Single testis
Eversible penis-injects sperm into
the pseudocoelom of female
(hypodermic impregnation)
Reproduction and Development
Divided into 3 classes:
class
order
Class Seisonidea
Females produce haploid eggs
that must be fertilized and
develop into either males or
females.
♀ & ♂ similar in size and form
Sexually reproduction only
Class Bdelloidea
Females are parthenogenetic
(asexual)- produce diploid
eggs that hatch into diploid
females.
Class Bdelloidea
"The study of rotifers is a study of
ladies, sometimes beautiful, often
capricious, always fascinating.“
(Meglitsch)
Class Monogononta
Females produce two kinds of
eggs:
–Amictic eggs- diploid eggs
that have not undergone
reduction division, cannot
be fertilized & develop only
into females.
Class Monogononta
–Mictic eggs- undergone
meiosis and are haploid- if:
• Unfertilized- develop quickly
into males
• Fertilized- they secrete a thick
shell and become dormant for
several months before
developing into amictic females.
Ecdysozoan
Phylum Nematoda
The roundworms
5 billion per acre
Phylum Nematoda
• Parasites and free-living
• Lack cilia except in their sensory
structures
• Marine, freshwater, and soil
habitats
• Triploblastic, bilaterally
symmetrical
• Unsegmented vermiform (wormlike
organism)
Phylum Nematoda
External features
• Noncellular, collagenous
cuticle
–Can molt 4 times during maturation
–Maintains internal hydrostatic
pressure
–Mechanical protection
–Resists digestion by the host
Phylum Nematoda
• Longitudinal muscles are used for
locomotion
– Thrashing movements (can’t crawl like
worms)
Phylum Nematoda
• Sensory organs
–Amphids – chemoreceptors
along the cuticle
–Phasmids - chemoreceptors
near the anus
–Ocelli – eyespots found in
aquatic nematodes
Feeding and Digestive System
Carnivores, herbivores, omnivores,
saprobes(decomposers), or parasitic
Complete digestive system
mouth->buccal cavity->pharynx
->tubular intestine->rectum->anus
Hydrostatic pressure pushes
food thru
Other Organ Systems
Glandular system
–Aquatic nematodes
–Renettes – absorb
nitrogenous waste
Tubular system
–Parasitic nematodes
–Renettes form a canal
Other Organ Systems
• Nervous system
–Nerve ring from anterior
to posterior
–Also have neuroendocrine
secretions involved in
growth, molting, cuticle
formation, and
metamorphisis
Reproduction
Sexual
–Dioecious-having separate sexes
–Dimorphic-males are smaller than
females
–internal fertilization
Reproduction
–Males
»One testis
»Bursa- used to insert
their sperm into the
female
»males have ameboid
sperm
Reproduction
–Females
»Pair of convoluted ovaries
»Oviducts become uterus
»Several hundred to
several hundred- thousand
eggs per day
»Ovovivparity – giving birth
to larvae that hatched
from an egg
Some Important Nematode
Parasites of Humans
• Ascaris lumbricoides
• Enterobius vermicularis
• Necator americanus
• Trichinella spiralis
• Wuchereria bancrofti
Ascaris lumbricoides
The Giant Intestinal
Roundworm- The adult
female worm can be over 30
cm long and 2-6 mm wide
800 million infected- most
common parasitic worm
disease in the world
Ascaris lumbricoides
Adults live in small intestines of
humans
Eggs exit with through feces
Once the eggs are ingested, they
hatch in intestine and travel to
the lungs
Larvae molt twice, they travel to
the trachea where they are
swallowed
Ascaris lumbricoides
Warning: those with weak stomachs need not
continue viewing. Only for the HBO
audiences!
When Ascaris
becomes a big
problem. . .
Enterobius vermicularis
Pinworm
Most common
parasite in US
Adults live in large
intestine
At night females
migrate out of the
anus and lay eggs
on skin
Enterobius vermicularis
Human ingest
eggs, hatch and
molt 4 times in
small intestine
& migrate to
large
Necator americanus
• Found in Southern US
• Adults live in small
intestine with teeth
and feed on blood &
tissue fluid
• Females 10,000 eggs
daily & pass out of
body in feces
Necator americanus
Eggs hatch in warm moist soil and
releases a small larva, the larva
molts and becomes the infective
filariform larva.
hookworms living in soil
Necator americanus
Humans become infected when
filariform penetrates the skin
(usually b/w toes) to reach our
circulatory system
Trichinella spiralis
The Porkworm
Adults live in mucus of small intestine
of humans and other mammals
Adult female
Adult male
Trichinella spiralis
Females birth young, larvae enter
circulatory system and are carried
to Skeletal (striated) Muscles
Larvae entering
into Skeletal
Muscle cells
Trichinella spiralis
Larvae encyst in muscles & remains
infective for many years
Another host
must ingest
infective meat
to continue the
life cycle
Trichinella spiralis
Humans become infected by eating
improperly cooked pork products
Larvae encyst in stomach move to
small intestine molt 4 times, turn
into Adults
Wuchereria bancrofti
The Filarial worms
In tropical countries over 250
million human infected
Wuchereria bancrofti
Thread-like worms that live in the
Lymphatic System, block the vessels
This causes enlargement of various
appendages: Elephantiasis
An Adult female Wuchereria
bancrofti is about 80-100 mm long
and 0.24-0.30 mm in diameter,
whereas a male is about 40 mm
long and 0.1 mm in diameter.
Elephantiasis
Warning: Pictures not for everyone!
Wuchereria bancrofti
Adults copulate produce
microfilariae.
The microfilariae released into the
blood stream
A microfilaria is about
240-300 µm
(micrometers) long and
7.5-10 µm thick
Wuchereria bancrofti
Mosquito (intermediate host) feeds on
human (definitive host) ingest
microfilariae and larvae molts 2 times
Mosquito bites another human it injects
3rd stage larvae into human blood, molts,
enters lymphatic system
Other Filarial Worms
Dirofilaria immitis in US parasite of dogs
Adult worms live in heart, large arteries,
and lungs
Heartworm disease- fatal to dogs, unless
give preventative medicine
Phylum Nematomorpha
• Phylum Nematomorpha
– Characteristics
250 species
Horsehair worms
Adults are free-living
Juveniles are parasitic in
arthropods
• No distinct head
• Dioecious
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