ACOELOMATE ANIMALS – animals __________________ a coelom
Phylum
Platyhelminthes – flat worms
Phylum
Nemertea – ribbon worms
Phylum
Gnathostomulida – jaw worms
I. General Features of Acoelomate
animals
A.
_______________________________
1.
Concentrating the sense organs on the head is an advantage to
active animals that seek food; this provides
an anterior and
posterior end and bilateral symmetry.
B. Position
and Biological Contributions
1. These
are the simplest animals with primary bilateral symmetry.
2. They
have a solid body without a coelom; they are the
_______________________________.
3.
Specialization of organs provides the organ-system level of
organization.
4. Along
with cephalization, this is the beginning of a
_______________________________of
nervous system.
5. The
simplest excretory or osmoregulatory systems appear.
6.
_______________________________ have the simplest
circulatory system and a one-way alimentary canal
with both mouth
and anus.
II. Phylum Platyhelminthes – the
flatworms
A.
Classification of Phylum Platyhelminthes
Class Turbellaria
Class Trematoda
Class Cestoidea
Class Monogenea
B.
Characteristics
1.
Flatworms vary from a millimeter to many meters in length.
2.
_______________________________ are mostly free-living in
aquatic or moist terrestrial environments; some
are symbiotic or
parasitic.
3. All
_______________________________ and
_______________________________
are parasitic.
4.
Parasitic flatworms may have several hosts in their life cycle;
some larvae may be free-living.
C. Form and
Function
1.
Tegument and Muscles
a. Most turbellarians have dual-gland adhesive organs.
1) Viscid
gland cells fasten microvilli of anchor cells
to the substrate.
2)
Secretions of releasing gland cells provide a
quick chemical detachment.
2.
Nutrition and Digestion
a.
_______________________________ have no digestive
system; they rely on the host’s digestive
tract and absorb
digested molecules.
b. The other flatworms have a mouth, pharynx and an
intestine.
Undigested food is egested back out the
_______________________________.
(They
have no _______________________________.)
c. Planaria Feeding
1) They
are carnivorous and detect food by
_______________________________.
2) They
entangle food in mucous secretions from
glands and rhabdites.
3) They
wrap themselves around prey and extend the
proboscis to suck up bits of food.
d.
Monogeneans and trematodes feed on host cells, cellular
debris and body fluids.
3.
Excretion and Osmoregulation
a. Most
flatworms have
_______________________________
with flame cells.
b. Collecting ducts join
and rejoin until they empty at
nephridiopores.
c.
Metabolic wastes are removed largely by diffusion through
the body wall.
4. Nervous
System
a.
One to five pairs of
longitudinal nerve cords lie under the
muscle layer.
b. In
most flatworms, the nerves are differentiated into
sensory, motor and association-types.
5. Sense
Organs
a.
_______________________________ are light-sensitive
eyespots in turbellarians,
monogeneans and larval
trematodes.
b.
Tactile and chemoreceptive cells are abundant, especially
in the ear-shaped auricles.
c. Some
have _______________________________ for
equilibrium and _______________________________ for
sensing direction of water currents.
6.
Reproduction and Regeneration
a.
Fission
1) Many turbellarians constrict behind the pharynx
and separate into two animals. Each half regenerates
the missing parts; this provides for rapid
population
growth.
b. Some
asexual reproduction occurs in intermediate hosts;
see life cycles to follow.
c.
Nearly all are _______________________________ but
_______________________________.
d. After
copulation, eggs and yolk cells are enclosed in a
small cocoon and attached by a stalk to
plants.
e.
Embryos emerge and resemble little adults; however,
some marine forms are ciliated and
free-swimming larvae.
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D. Class Turbellaria (e.g. ___________________) 1. Planaria, which are very small, swim by cilia. 2. Others
move by cilia and gliding over a slime track
secreted by marginal adhesive glands. 3.
Rhythmical muscular waves pass backward from the head. 4.
_______________________________ |
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E. Class Monogenea
1.
Monogeneans are external parasites of ___________________,
especially gills, but a few are found in bladders
of frogs and turtles.
2.
Monogeneans have a _______________________________ life
cycle in a _______________________________
host.
F. Class Trematoda (the _______________________________)
1. Most
adults are _______________________________ of
_______________________________.
2. Adaptations for parasitism
include:
a. penetration glands,
b. glands to produce cyst material,
c. hooks and suckers for adhesion, and
d. increased reproductive capacity.
3. Sense
organs are poorly developed.
4. Subclass
Digenea –
includes the serious fluke parasites of
humans and domestic animals.
a.
Nearly all have an indirect life cycle with the first
_______________________________
host being a
_______________________________.
b. The
_______________________________ or final host
is a vertebrate.
This is where
_______________________
_______________________________occurs.
c. A
second or third intermediate host may be required in the
life cycle.
d. They
parasitize a wide range of hosts and most parts of
most systems in hosts.
e. General Digenean
Life Cycle
1) The egg passes from the
definitive host in excreta
and must reach water.
2) The egg
then hatches into a free-swimming ciliated
larva, the miracidium.
3) The miracidium penetrates the tissues of a snail and transforms
into a sporocyst.
4) The sporocyst reproduces asexually into more
sporocysts or many rediae.
5) Rediae reproduce asexually into more rediae
or
into cercariae with
tails.
6) Cercariae emerge from the snail and penetrate a second
intermediate host or encyst on objects to become metacercariae,
or juvenile flukes.
7) The adult
grows from a metacercaria when it is eaten by the
definitive host.
6. Sheep Liver
Fluke - _______________________________
was the first digenean
whose life cycle was described.
Watch this video of a cow liver fluke turning ants into “zombies!”
This is
caused by the trematode Dicrocoelium dendriticum, known as the lanceolate fluke.
7. Liver
Fluke in Humans - _______________________________
a. This is
the most important human liver fluke; it is common
in
b. It also
infects cats, dogs and pigs.
c. Clonorchis
Life Cycle (courtesy CDC below).
d. Control is achieved by:
__________________________
___________________________________________
__________________________________________.
8. Blood
Flukes - _______________________________
a. Over
200 million people have ______________________,
infection with blood flukes, commonly in Africa,
South
America,
West Indies, and the Middle and Far East.
b. It is
unusual insofar as sexes are separate (they are
______________________).
1) The male
is larger with a gynecophoric canal to
embrace a smaller female.
c. Schistosoma Life Cycle (courtesy CDC) below.
d. _____________________________________________
(swimmer’s itch)
occurs when cercariae penetrate an
unsuitable host such as a human.
9. Lung Flukes –
_______________________________
_______________________________
is a lung fluke that
parasitizes humans, pigs, rodents, etc.
a. Its eggs are
coughed up in ________________________,
then swallowed and eliminated in feces.
b. Metacercariae develop in _________________________;
human infection occurs by eating uncooked
crabmeat.
c. Control is by ___________________________________
_______________________________________________.
10.
_________________________________________________,
another trematode, lives in human intestines in
is contracted from eating raw aquatic
vegetation.
G. Class Cestoidea (the _______________________________)
1. General tapeworm characteristics
a. A unique flattened and segmented shape
compared to
other
flatworms.
b. Each trailing segment is a
_______________________________
containing a set of
_______________________________
organs.
1)
Proglottid formation is not “true”
segmentation;
replication
of sex organs is not equivalent to
metamerism in annelids, etc.
c. The tegument is syncytial and has no cilia.
d. The entire
surface of cestodes is covered with projections
(they look like microvilli seen in vertebrate small
intestines);
these _______________________________ increase
the
surface area for food absorption.
e.
Nearly all are _______________________________.
f. They
lack sensory organs except for modified cilia.
g. The _______________________________
is a holdfast
head portion with suckers and hooks.
h.
Nearly all cestodes require two hosts; the adult is
parasitic
in the digestive tract of the
__________________________.
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2. Characteristics of Subclass Eucestoidea –
tapeworms that affect humans. ·
The
chain of proglottids is called a strobila. ·
Proglottids
originate in the germinative zone just
behind the scolex. ·
A
proglottid is usually fertilized by another proglottid in the same or different strobila. ·
Shelled
embryos form in the uterus; they are either expelled or the whole proglottid is shed. ·
Over
1000 species of tapeworms are known, infecting almost all vertebrates. Most tapeworms do little harm to the host. |
3. Beef
Tapeworm – ____________________________________
a. This
tapeworm lives as an adult in the alimentary canal of
humans; the juvenile form is found in
_______________________________
tissue of
_______________________________.
b.
Mature adults can reach over
_______________________________
in length with
over _______________________________ proglottids.
c. The scolex has four suckers but no hooks.
d.
_______________________________ proglottids (with
shelled, infective larvae) pass in
_____________________.
e. Each
mature proglottid has muscles and parenchyma plus
male and female organs.
f.
Gravid proglottids usually crawl out of feces.
g. Proglottids rupture as they dry; embryos are viable for
_______________________________
and are picked up by
grazing.
h. Life
Cycle
i. Infection can be avoided by
________________________
________________________________________________.
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Neural
cysticercosis
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4. Pork Tapeworm _________________ a. This
tapeworm lives as an adult in the _____________________ of humans; juveniles live in muscles of
____________________________. b. If eggs
or proglottids are ingested,
the embryos migrate to organs and form _____________. c.
_________________________ commonly
occurs in ___________ or the
_______________ causing expected symptoms or death. d.
Infection can be avoided by ___________________________. |
5.
. Fish Tapeworm - Diphyllobothrium latum
a.
Adults are found in intestines of humans, dogs, cats and
other mammals; immature stages are in
crustaceans and
fish.
b. It is
the largest cestode of humans, reaching up to 20
meters long.
c. Fish
tapeworms may occur when people eat raw fish.
6. Unilocular Hydatid - Echinococcus granulosus
a.
Adults parasitize dogs and other canines; juveniles infest
many mammals.
b.
Humans may serve as an intermediate host.
c. A
juvenile is a special cysticercus, a hydatid cyst,
that
grows for up to 20 years to a huge size.
d.
Surgical removal is the only treatment.
e. Infection occurs when people play with dogs or
work in
soil where dogs have defecated and then fail
to wash their
hands.
III. Phylum Nemertea - ribbon worms
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Nemerteans are dorsoventrally flattened. They are the simplest animals with a blood-vascular
system. ·
The
blood-vascular system has a single dorsal vessel and two lateral vessels. ·
Blood
is colorless and contains nucleated corpuscles. ·
There
is no heart; blood is moved by muscular walls of blood vessels and by body
movements. ·
Respiration
occurs through the body surface. Most are marine. Most nemerteans
are carnivorous and eat dead or living prey. |
IV. Phylum Gnathostomulida – jaw worms
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·
Over
80 species of jaw worms in 18 genera have been described. ·
They
are delicate worm-like animals, 0.5 to 1 mm long. ·
They
live in crevices of sediment and silt and endure low oxygen; they are often
very common. |
V. Phylum Gastrotricha
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·
Gastrotrichs
are similar to rotifers but are ventrally flattened, lack a corona and mastax, and are bristly or scaly. o They live in the interstitial spaces
between benthic (the bottom of seas or lakes) particles of sand or mud. ·
Gastrotrichs
are hermaphroditic. o Some eggs are thin-walled and rapidly
develop, and some are thick-shelled for long dormancy. o Development is direct; juveniles have
the same form as adults. |
