Download Unit 5 Animals

ANIMAL KINGDOM 1
EVOLUTIONARY TRENDS and PHYLUM PORIFERA
1. Describe the biological definition for an animal.
2. Identify the 4 major trends in the evolution of animals.
3. Describe the differences between a protostome and a deuterostome.
4. Identify 3 germ layers that form from a blastula and describe what structures
they give rise to.
5. Identify the unifying characteristics of the phylum Porifera.
6. Examine the process of filter feeding in a sponge. Label a sponge identifying
the functions of the following: archaeocytes, spicules, choanocytes, pores and
osculum.
7. Identify the reproductive cycle of Poriferans as having a haploid and diploid
stage.
PHYLUM CNIDARIA
8. Examine members of the phylum Cnidaria and describe characteristics that
unify each.
9. Explain the advantages to a Cnidarian of having the tissue level of
organization versus the cellular level of organization shown in Protists.
10. Name three classes of Cnidarians and give their characteristics. Put members
studied in class into their proper classes.
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11. Label a hydra, an Obelia colony, and a medusa using the appropriate terms:
Gastrovascular cavity (GVC), nematocyst, tentacle, ectoderm, mesoglea,
endoderm, bud, gland cell, flagellated cell, basal disc, feeding polyp, radial
canal, gonad, ovary, testis, ring canal, mouth bell.
12. Explain how a hydra and an Obelia colony captures food and then ingests,
digests (include extracellular and intracellular) and egests.
13. Explain how hydra and Obelia reproduce sexually and asexually, how they
respire and how they excrete. Include the meaning of ‘alternations of
generations’ as it applies to Obelia.
14. Describe the anatomy of coral. State its importance to oceans.
PHYLUM PLATYHELMINTHES
15. List the characteristics of the Phylum Platyhelminthes (flat worms)
16. Name three classes and give their characteristics. Put the animals studied
into their proper classes.
17. Label the anatomy of the planaria, the liver fluke and the tapeworm using the
appropriate terms from the following list: Auricle, eyes, brain, pharynx,
anterior and posterior ends, ventral surface, dorsal surface, GVC, scolex,
uterus, testis, vas deferens, oviduct, vagina, ovary, mature proglottid, gravid
proglottid, hooks, suckers.
18. Describe the life cycle of the planaria, liver fluke and tapeworm. Use the
terms: miracidium, sporocyst, cercaria, intermediate host, final host,
6-hooked larva, bladderworm.
19. List three adaptations of members of this phylum to a parasitic way of life.
20. Describe methods of preventing the spread of the parasites studied.
21. Describe how a planaria carries out the following life activities by describing
the structures used for: ingestion, digestion, egestion, respiration, and
excretion (include flame cells, excretory tubules, and excretory pores)
22. Explain why the possession of a mesoderm can be a problem. Explain how
the planaria compensates for having a mesoderm.
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PHYLUM PORIFERA (Sponges - a loose collection of cells)
All of the sponges belong to the Phylum Porifera (which means “pore-bearers”)
Sponges inhabit all the seas including polar and tropical seas, lakes and streams.
Sponges are classified as animals because they fit into the biological definition of
an animal. They, like us, are multicellular eukaryotic heterotrophs whose cells
lack cell walls. The sponge as an animal goes through all of the life activities
characteristic of animals.
Poriferans are unique from other animals in several ways:
 They are a “loose collection of cells”. This means that sponges do not form
distinct layers of cells as is found in all other animals.
 They rely on “filter-feeding” to obtain nutrients
 They have no mouth or gut, no specialized tissues or organ systems
Sponges do have specialized cells that perform specific tasks that allow the loose
assemblage of cells to function as a unit. You will learn the role of each of these
cells as you investigate Sponges. These cells include:
Pore cells
Collar cells (Choanocytes)
Archaeocytes cells
Spicules
Role of Sponges
In their aquatic environment Sponges have various roles with the organisms they
interact with.
 Form symbiotic relationships with bacteria and Protists. Sponges can
provide food for these organisms as well as exchanges of O2 and CO2.
 Sponges are food for snails, sea stars and various fish.
 Scientists use Sponges for the chemicals that they secrete when protecting
themselves from various fungi and other pathogens. These chemicals have
produced powerful antibiotics and even anti viral drugs. They have also
found limited use for treatments of leukemia, herpes and resistant strains
of streptococcus bacteria.
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Investigation Sponges
Reference pgs.664-667
Sponges are among the most ancient animals alive today. They are heterotrophic
and multicellular but very simple aquatic animals. Sponges lack specialized
tissues or organ systems. They are a loose collection of specialized cells. Fill in
the labels listed in the diagram below.
1. Describe the function of each of the following structures:
Osculum _______________________________________________
_____________________________________________________
Pore __________________________________________________
______________________________________________________
Spicule_________________________________________________
______________________________________________________
Archaeocyte _____________________________________________
______________________________________________________
Choanocyte ______________________________________________
______________________________________________________
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2. Name the structures in a sponge that an indigestible particle (carried in water)
would go through. Remember that a sponge does not keep this particle.
______________________________________________________
______________________________________________________
3. Name the structures in a sponge that a food particle would go through.
Remember that a sponge wants to keep this particle of food.
______________________________________________________
______________________________________________________
4. Complex sponges have folds in their body walls. On the left is a simple sponge
and the right is a complex sponge. Which sponge structure A or B below can
move water through its body faster? Give an explanation why?
A
B
______________________________________________________
______________________________________________________
5. Cholcicine is a chemical that stops the action of flagella. What would happen
to a sponge if cholcicine was present in the water in which they live? Explain?
______________________________________________________
______________________________________________________
______________________________________________________
6. What would happen to a sponge living in a limited supply of stagnant water?
______________________________________________________
______________________________________________________
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CNIDARIANS
Two Layers of Cells
The Hydra lives in ponds, lakes, and streams, attached to rocks or water plants by a sticky secretion from its
basal disc. The body, with its tentacles encircling the mouth, looks like a centimeter of string with the
unattached end frayed out into several strands. Because of its small size, transparency and habit of
contracting down into a little ball when disturbed, the animal is readily overlooked. Yet, hydras are
abundant and are the only really successful ones among the few members of their phylum that have
invaded fresh water. The salt-water or marine relatives of the hydra — the jelly fishes, sea anemones, and
corals — are the better known of the phylum Cnidaria. The phylum Cnidaria used to be called phylum
Coelenterata which literally means “hollow-gut”. This refers to the fact that the main cavity of the body is
the digestive cavity called the gastrovascular cavity otherwise known as the GVC.
Beginning with the Cnidarians, all “higher animals” have a digestive cavity which connects with the outside
through a mouth. For this reason, among others, it is accepted that modern Cnidarians, unlike sponges,
evolved from the same stock that gave rise to all the more complex phyla.
The hydra consists of two layers of cells. The outer layer, or ectoderm
is a protective layer of cells as in sponges but Cnidarians contain
several other kinds of cells. The inner layer of cells called the endoderm
lines the internal cavity and has a primary function of digestion. The
ectoderm has muscle fibres that run lengthwise. When they contract
equally on both sides, the body shortens into a tiny ball. When they
contract more on one side than on the other, the body is bent in the
direction of greatest attraction. The muscle fibres in the endoderm layer
run circularly; and when they contract, the body becomes narrower and
longer. Between the two layers lies a jelly-like non-cellularlayer called the mesoglea.
FEEDING
In feeding, the hydra does not chase its prey, but remains attached to a rock or plant in a favorable
environment with almost motionless tentacles trailing in the water. When a small crustacean or worm
brushes one of the tentacles in passing, the unlucky victim is suddenly riddled with a shower of poisonous,
numbing threads shot out of structures called nematocysts. Each nematocyst consists of a fluid-filled
capsule containing a long spirally coiled hollow thread. These nematocysts arise from specialized ectoderm
cells called cnidocytes found mainly on the tentacles of the hydra. The cnidocyte has a small trigger
projecting from the surface. When the trigger is stimulated, a physiological change occurs, such that the
pressure within the fluid-filled capsule is suddenly increased and the nematocyst is discharged with such
explosive force that it pierces the body of
its prey and injects a poisonous substance
contained in the capsule. After the poison
from a number of nematocysts has begun
to paralyze a small victim, the tentacles
are wrapped around the prey and contract
drawing the prey toward the mouth, which opens widely to receive it. The victim is now swallowed into the
GVC by means of muscle contractions aided by slimy secretions from gland cells lining the inside of the
mouth. A nematocyst can be discharged only once. Used ones are discarded and are eventually replaced
with new ones.
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DIGESTION
Digestion takes place in the interior cavity called the gastrovascular cavity or GVC. Gland cells in the
endoderm secrete chemicals called enzymes which break-down or digest protein and fatty substances (the
digestible parts of the prey) into a soupy-like suspension. This material is then engulfed by the pseudopodal
activity of ameboid cells. The process of digestion is completed within food vacuoles in these cells, for
the hydra has retained, in part, the protists method of food ingestion and digestion. Since the mouth region
and thus the GVC is continuously open to the environment it has been said that digestion occurs in two
ways in the hydra. The first is extracellular digestion. Extracellular digestion occurs in the GVC with the
aid of the gland cells spewing their enzymes on the food. The second is called intracellular digestion
and requires the ameboid cells engulfing the products of extracellular digestion and then developing food
vacuoles to pass the food from cell to cell by diffusion. The GVC is able to circulate the food throughout the
cavity of the body and hollow tentacles. The GVC thus has the double function of digestion and circulation.
That is why it is called the gastrovascular cavity which means, “stomach-circulatory” cavity.
REPRODUCTION
When well fed and healthy, hydras will reproduce asexually by budding. The buds occur about one-third
the length of the body up from the basal disc. The bud looks like a projection which elongates and soon
sprouts tentacles at its outer end. In two or three days the bud looks like a little hydra, complete with stalk,
tentacles, and mouth. At its base, the GVC of the bud is continuous with that of the parent, and in this way
it receives nourishment. Shortly after this it constricts or pinches off from the parent and begins its own
independent life. The asexual budding process produces new hydras that are genetically identical to the
parent hydra.
Hydras have the curious ability to regenerate lost or damaged tentacles when injured. Even if the hydra is
cut into a number of pieces, most of the pieces will grow the missing parts and become complete and
independent hydras.
Hydras reproduce sexually at certain times of
the year, generally in fall or winter. In some
species both male and female sex cells occur
in the same individual, which is then known as
a hermaphrodite. In certain regions of the
hydras body, cells start to grow rapidly causing
a bulge in the body wall. Such bulges known
as testes when filled with sperm forming cells
and as ovaries when filled with egg forming
cells. It is not definitely known how the
formation of sex cells occurs. One of the
factors may be low temperature that stimulates
the growth of testes and ovaries. It is also
known that abundant food can sometimes
stimulate the development of sexual maturity.
Ripened eggs continue to grow until the egg
breaks through the ectoderm covering and projects
with its outer surface exposed to the water.
Sperm, discharged from a testis, swim through
the water and surround the egg; one enters and
causes fertilization. If the egg is not fertilized within
a short time after it is first exposed, the egg will
die and disintegrate.
Development begins, as in sponges and nearly all
other multi-celled animals, with the division of the Fertilized egg or zygote into two cells. These cells
promptly divide, forming four cells. Continued division results in a one-cell-layered ball known as a
blastula. In the hydra the blastula cells continue to divide as some of the surface cells migrate inward to
form the beginning of an interior cavity that will eventually become the endoderm layer. In this two layered
stage called a gastrula. The gastrula hardens and usually drops off from the parent and becomes fastened
by a sticky secretion to a surface. Under favorable conditions the young hydra may hatch from the shell
after a week or more. In winter, the egg may lie dormant until the following spring.
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BEHAVIOUR
The behavior of the hydra is much more varied and complex than that of the uncoordinated sponge. The
many celled hydra has a network of nerve cells extending throughout the entire animal. This nerve net is
slightly more concentrated around the mouth than elsewhere. There is no brain controlling the nerve net.
The nerve net is thought to be composed of separate nerve cells arising from the mesoglea, which is not a
true layer of cells but rather a loose connection of individual cells. The hydras reflexes are poor. A hydra
must contract and respond to a stimulus with its whole body rather than just an individual tentacle or body
part. The development of simple reflexes seems to be sufficient for the hydra. More complex multi-celled
organisms have evolved their nervous systems enough to show specific local responses to stimuli, for
example, the ability to blink our eyes or withdraw a hand without having to contract all the muscles in the
body as does the hydra.
All the essentials of a simple nervous mechanism
in multi-celled animals are present in hydra.
Stimuli are received by sensory cells that are
peculiarly sensitive to touch or to chemical
substances in the water. These are slim, pointed
cells scattered among the cells of both layers, and
lying with their pointed ends projecting to the
outside if in the ectoderm, or into the digestive
cavity if in the endoderm or gastroderm. Sensory
cells send impulses to nerve cells which in turn
send their impulse to muscle cells which contract
or gland cells which squirt out digestive enzymes
into the GVC.
Even non-living things can respond to stimuli. If
you push over a rock, it may “respond” by rolling
over; but in doing so, it may roll down a hill and
break as it strikes some other rocks. The response
of a hydra, or of any other living organism, however,
is usually adaptive, that is, the response results in
a favorable adjustment of the animal to its
the nerve net of a hydra
environment.
If a hydra is touched, the sensory cells receive the stimulus. The change started in them by the touch
affects in some way, the nerve cells of the network and causes them to transmit a stimulus to muscle fibers,
which contract, shortening the hydra and getting it out of the way of the “offending” object.
The nerve net not only transmits impulses but also co-ordinates the hydra’s activities. When a small animal
touches one tentacle, the other tentacles will finally come to grasp the prey and will work together to cram
it into the mouth, which has already opened in response to chemicals leaking from the food. The nerve net
likewise co-ordinates the muscular contractions involved in swallowing food or in forcibly removing
indigestible particles. Thus it enables an animal composed of many thousands of cells to react as one
integrated individual. The importance of co-ordinated activity is emphasized by what happens when it fails.
Sometimes the hydra swallows its food so rapidly that it takes in one or more of its own tentacles, and the
hydra has even been observed to swallow its own base along with the prey. Fortunately, it does not digest
its own cells, and after a time the swallowed parts emerge, apparently uninjured.
LOCOMOTION
Hydra can simply glide on the base of their discs due to a creeping amoeboid movement of these basal
cells. The most rapid method of locomotion is a kind of somersaulting action. Some hydras can even
extend their tentacles and latch onto another surface by releasing their basal discs. A hydra will move away
from water at which the temperature approaches 25˚ C. Many species can even tend to move toward light.
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OBELIA
The nearest marine relatives of the hydras are the branching colonial cnidarians known as the Obelia.
Obelia form delicate plant-like growths on rocks and wharf pilings along the seacoast. The colonies are
about 2 to 7 cm in height. The colony arises from budding from a single hydra-like individual. The bud fail
to separate, and after repeated budding, there results a treelike growth, permanently fastened to some
object and consisting of numerous members united by stems. More often, any single individual of a colony
is referred to as a polyp.
Polyps and stems are protected and held erect by a horny covering
secreted by the ectoderm, which encloses all the stems and extends
around each polyp as a transparent cup, shaped like a goblet. When
irritated, the polyp can withdraw into this cup; and the rapid contraction
and slow expansion of the polyps are about the only movements that
can be seen in an Obelia colony. The stems are unmovable because
of the rigidity of the covering; but at certain points the covering is
arranged in rings, which allow for flexibility as the stems are swayed
by water currents.
An Obelia polyp is built on the same plan as a hydra, and consists of the same two layers, endoderm and
ectoderm. These are made of similar cell types to those of the hydra.
FEEDING
The Obelia feeds in the same way as the hydra, capturing small prey by means of tentacles armed with
nematocysts. The tentacles are not hollow, as in the hydra, but are solid, having a central core of large
endodermal cells. The polyps and stems are hollow, and the GVC of every polyp is continuous with that of
every other polyp in the colony. The food is partly digested in the cavity of the polyp, and the resulting
fluid is circulated about through the stems by the actions of the GVC. Thus food is distributed throughout
the colony in thoroughly cooperative fashion, and digestion is completed in food vacuoles within the cells
lining the gastrovascular cavity.
REPRODUCTION
The way that Obelia reproduces along with its colonial nature are two of the main reasons why we study
this organism. Asexual reproduction by budding is the usual method of increasing the number of
polyps. In addition to continuous budding even the stems tend to grow horizontal shoots over the surface
and then give rise to new colonies so that over time the entire colony may, after a time consist of hundreds
of individuals. Sexual reproduction does not occur in the polyp colony. There are never any signs of testes
or ovaries as we might find in the hydra.
Where Obelia is different is that all the polyps are not alike. There are feeding polyps that have tentacles
with which they catch prey. When looking closely at some of the polyps that branch off of the main stem,
there occur reproductive polyps. These polyps have lost their tentacles and the capacity to feed, and are
nourished through the activities of the feeding members of the colony. Inside the reproductive polyp are
saucer-like buds stacked one on top of each other. The most developed near the top of the polyp, the least
near the base. As the top-most “saucer” matures it escapes through an opening at the upper end of the
polyp and swims away as a tiny animal called a medusa. The medusa of the Obelia looks like a typical bellshaped jellyfish however, miniature in size. The medusa jellyfish has the same general body plan as all
Cnidarians. There are two cell layers, a non-cellular mesoglea, a gastrovascular cavity and nematocysts.
The primary function of the medusa is sexual reproduction.
From the underside of the bell hang four sex organs called gonads. In female medusas they are the
ovaries and produce eggs; in male medusas they are testes and produce sperm. Eggs and sperm are shed
into the sea water, where fertilization takes place. The fertilized egg becomes a zygote, then a blastula with
two cell layers and eventually a ciliated larva which swims around for a time, settling on a rock or on a
piece of kelp. The larva will grow tentacles and a mouth and eventually become a new polyp. The polyp by
asexual reproduction produces a new colony of sessile polyps. The larva and the free-swimming medusas
both serve as a means of spreading the Obelia to new localities.
Although the medusa form looks radically different from the polyp form, they do as mentioned have the
same internal body plan that is consistent with all Cnidarians. The chief difference from the polyp is the
thickness of the mesoglea, the jelly-like substance between the two cellular layers. In the absence of
supporting structures like the spicules of sponges or the connective tissue of higher animals, the jelly gives a
firm consistency to the otherwise fragile body and adds to its buoyancy. The polyp and medusa may be
regarded as having adapted the same general pattern to two different ways of life… attached and free
swimming.
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The fact that Obelia lives its life in two forms, the medusa and polyp, is a phenomenon known as
polymorphism. The Obelia really has three kinds of individuals: the feeding polyps, the (asexual)
reproductive polyps, and the (sexual) reproductive medusas, each with its own functions.
The life history of Cnidarians may be interpreted as follows: The ancestral Cnidarian was a medusa-like
form which produced other medusas directly from eggs and sperm, by way of a larval stage resembling a
polyp. Eventually, this larval polyp-like stage became more and more important in the life history and took
on an independent existence. At first the polyps were incapable of sexual reproduction and would grow up
into medusas, which produced egg and sperm. But some Cnidarian polyps eventually developed the
capacity for forming sex cells and dropped out the medusa stage altogether, as has happened in the Hydra.
Cnidarians form a number of interesting symbiotic relationships with other animals. Certain fish, shrimp,
and other small animals live among the tentacles of large sea anemones. The sea anemone protects and
provides scraps of food for these fish which are unaffected by the anemones nematocysts. In return the
fish are thought to help clean the sea anemone and protect it from certain predators.
Corals and the reefs they form are extremely important in the ecology of tropical oceans. Because coral
reefs are built from many separate coral colonies attached together, they contain tunnels, caves, and deep
channels. In these recesses live some of the most beautiful and fascinating animals in the world. Corals
are important to humans in many ways. Coral reefs provide homes for food fishes and other edible animals,
as well as for organisms that produce valuable shells, pearls and other products. Reefs also protect the land
from much of the action of waves. When coral reefs are destroyed or severely damaged, large amounts of
shoreline may be washed away. Fossil reefs offer important clues to geologists about the location of oil
deposits. Large blocks of coral have been used to build houses and to filter drinking water. Humans have
long used certain corals to make jewelry and decorations. Coral reefs are the only living structures that can
be seen from outer space aboard the space shuttle.
Some Cnidarians are used in medical research. Chemicals that they produce to protect themselves in their
environments may provide us with anti-cancer drugs and help us understand the disease in other ways.
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Digestion begins in the GVC and is completed intracellularly after gland cells in
the gastrodermis layer break down the food particles extracellularly.
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Cnidarian Lab
Make sure to read the manual on pages 7 - 13 before you do this lab.
Blk: ____
Name: __________________
Name: __________________
1. Place a living hydra in a watch glass with a daphnia. Observe it with a
dissecting microscope and answer the following questions:
2. Touch the hydra with a toothpick gently.
What can you conclude about its body based on its response?
_____________________________________________________
3. Explain how the hydra catches and eats food.
_____________________________________________________
_____________________________________________________
_____________________________________________________
4. By looking at the prepared slide of the hydra, the chart, and your lab manual,
how many cell layers are there? Name the layers.
_____________________________________________________
5. What is found between the two layers?
_______________________________________
6. In each layer, identify two special kinds of cells.
_____________________________________________________
_____________________________________________________
7. When compared to sponges, why is two cell layers considered to be an
evolutionary advancement over just a loose collection of cells?
_____________________________________________________
8. Obtain a slide of a hydra with bud.
What type of reproduction is represented by budding?
_________________________________
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9. Obtain a slide of an Obelia colony. From the slides and wall chart of the
Obelia, how do the feeding polyps and reproductive polyps differ?
_____________________________________________________
Label your diagram of an Obelia by using the Obelia chart and lab manual.
10. Explain what “alternation of generations” in the Obelia means.
_____________________________________________________
Class Scyphozoa
11. Go and look at the Aurelia and the diagram of its life cycle.
Why is it placed in a different class than the Hydra and Obelia?
_____________________________________________________
Class Anthozoa
12. Look at specimens of coral, and sea anemones provided.
What is a unique characteristic about organisms in this class?
____________________________________________________
Conclusion:
List the characteristics common to all members of this phylum.
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
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PHYLUM PLATYHELMINTHES (Flatworms)
Platyhelminthes include many free-living species such as planaria and two
important groups of parasites, the flukes and the tapeworms.
*Flatworms have three cell layers.
*Flatworms possess bilateral symmetry (left and right sides are mirror images of
each other)
*Cephalization
Flatworms are hermaphroditic
(*indicates an evolutionary advancement over Cnidarians.)
The mesoderm contains many structures that allow the flatworm to perform
many functions for a primitive nervous system, excretory system, digestive
system, and reproductive system. Unfortunately, the mesoderm is isolated from
its environment (its surrounded with endoderm and ectoderm). The flatworm
compensates by:



Being flat. An increase in its SA to V
Highly branched GVC
Excretory pores and flames cells
Evolving a parasitic way of life can also compensate the problem of having a
mesoderm by reducing the energy needed to obtain nutrients.
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PLATYHELMINTHES (Flatworms)
Three Layers of Cells
Put a piece of raw meat into a small stream or spring and after a few hours you may find it covered with
hundreds of black worms that are feeding upon it. These worms, each about one or two centimeters long are
called Planaria. When not attracted into the open by food, they live conspicuously under stones and on the
vegetation.
Planaria belong to the phylum Platyhelminthes, which literally means “flat-worm”. These flatworms
include many free-living marine species and two important groups of parasites, the flukes and the
tapeworms. There are many species of planaria just as there are many kinds of Amoebas and hydras.
The planaria differs from the hydra in that one end of the body has a definite head, with eyes and other
sense organs. The head is always directed forward in locomotion; and the body is clearly differentiated into
front, or anterior, and the rear, or posterior, ends. The planaria has an elongated flattened body; and if
we watch it move, we can see that one surface of the body always remains upward while the other is kept
against the bottom. The upper surface is termed dorsal (meaning back), and the lower surface, ventral
(meaning belly).
BODY PLAN
Beginning with flatworms all more complex animals have a layer of cells between the ectoderm and
endoderm called the mesoderm. This layer gives rise to muscles and to other structures which make
possible an increasing complexity and efficiency in animal activities. The Cnidarians were animals organized
on the tissue level. Their cells worked together to form two layers of tissues. From flatworms to humans, the
animals are organized on a still higher level. Not only do cells work together to form tissues, but tissues of
various kinds are closely associated to form one structure called an organ which is adapted for the efficient
performance of one function. An organ usually co-operates with other organs or parts in the performance of
some life-activity, and such a group of structures devoted to one activity is called an organ-system.
Flatworms do not have a lot of these organ systems and the ones they do possess are not very well developed;
but they are the lowest phylum of animals built on the organ-system level of construction.
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DIGESTION
In the digestive system of planaria the mouth , curiously enough, is not on the head but near the middle of
the ventral surface. It opens into a cavity that contains a tubular muscular organ, the pharynx. The
pharynx contains complex muscular layers and many gland cells. By means of the muscles, the pharynx can
be greatly lengthened and then protruded from the mouth for some distance; it behaves in this way during
feeding. Planarians feed on small live animals or on the dead bodies of larger animals. They can sense the
presence of food from a considerable distance by means of sensory cells on the head. They move toward
their food, mount upon it, and press it against the bottom by means of their muscular bodies. Struggling
prey can be successfully held in this way, especially after they have become entangled in the slimy secretion
from the worm. The pharynx is protruded through the mouth and inserted into the prey. It secretes
enzymes that soften the prey tissue, and its sucking movements tear the tissue into microscopic bits which
are swallowed along with the juices of the prey.
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From the anterior attached end of the pharynx the rest of the digestive system extends throughout the
interior of the animal. From the pharynx there is one anterior branch and two posterior branches. All three
branches of this gastrovascular cavity have numerous and fairly regularly spaced side branches, thus
providing for the distribution of the food to all parts of the body. The GVC is of course lined with cells that
make up the endoderm.
There is some digestion of food in the GVC such as in Cnidarians, but the food is broken up into small
particles before it enters the cavity, and is mostly ready to be taken up by endodermal cells in Amoeboid
fashion and formed into food vacuoles. The digested food is absorbed and passes by diffusion throughout
the tissues of the body. There is only one opening to the GVC, so undigestibles are eliminated through the
mouth as in the hydra.
EXCRETION
The region between the ectoderm and the endoderm called the mesoderm is filled with various organs and
specialized cells. The excretory system lies in the mesoderm layer and consists of a network of fine tubules
which run the length of the animal
on each side and open to the surface
by several minute excretory
pores. Side branches from these
tubes terminate in tiny structures
called flame cells. Each flame cell
has a hollow center in which beats a
tuft of cilia that simulates a
flickering flame. As the cilia beat,
extra body fluid gets drawn into the
flame cell and passed into the
tubule network of the excretory
canal and eventually out through
an excretory pore.
This flame cell system is analogous
to the contractile vacuoles of
Paramecium and appears to
function
primarily
for
the
regulation of water content of the
tissues.
23
REPRODUCTION
The planaria has a highly complicated reproductive system for sexual reproduction. We saw that sponges
have cells that can become egg and sperm and that in Cnidarians cells can aggregate into simple ovaries and
testes, which discharge their contents, the eggs and sperm directly to the exterior water. In Planarians,
ovaries and testes arise in the mesoderm; but there is a system of tubules and chambers in which
fertilization occurs, and there are complicated sex organs for the transfer of sperm. The animals are
hermaphrodites, forming both male and female sex organs in every individual; although crossfertilization amongst different planaria usually takes place to ensure genetic diversity. After the reproductive
season the reproductive structures degenerate and is regenerated anew at the beginning of the next sexual
period.
When sexually mature, each individual has a pair of ovaries close behind the eyes. From each ovary, a tube,
the oviduct, runs backward near the ventral surface. Yolk glands nourish the eggs. There are numerous
testes connected to a sperm duct . The penis extends into the genital chamber and transfers sperm during
mating. Sperm is deposited into the copulatory sac where the fertilized eggs are passed into the water and
will hatch little worms in two or three weeks.
Many planaria have no method of
reproduction other than sexual, but
some multiply asexually.
In this process, a region below the
pharynx pinches off and then both
sections grow a complete new body.
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NERVOUS SYSTEM
In flatworms, we see the first appearance of a central nervous system, the kind of nervous system
possessed and further centralized by all higher animals.
In the planaria there is in the head a concentration of
nervous tissue in a mass called the brain. From the
brain, two strand-like concentrations of nerve cells, the
nerve cords, run backwards through the body near
the ventral surface. From the ventral nerve cords
numerous side branches occur and are connected with
each other by many cross-strands like the rungs in a
ladder. Oddly enough, the brain does not control the
muscular movements required for swimming and a
planaria can still swim with its brain removed. It serves
chiefly as a sensory relay that receives stimuli from the
sense organs and sends them to the rest of the body.
The result is a much more closely knit behavior than is
possible with the non-centralized, diffuse nerve net of the
Hydra.
The external world is sensed by the sensory lobes, pointed
Projections on each side of the head. These are sensitive to
touch and water currents, as well as food and other chemicals.
The two eyes are sense organs specialized for light reception.
Each eye consists of a bowl of black pigment filled with special
sensory cells whose ends continue as nerves which enter the
brain. The pigment shades the sensory cells from light in all
direction but one, and so enables the animal to respond to the
direction of light.
By having abundant sensory cells, specialized sense organs, and
a central nervous system, the planaria shows a more varied
behavior and much more rapid responses than does the hydra.
Planaria generally avoid light and are generally found in dark places
under stones or leaves or water plants.
The flatworms are advanced over two-layered animals in a number
of important characteristics which are possessed by all higher
animals. The flatworms are the first to show bilateral symmetry
and cephalization. They are also the first to make extensive use
of a third layer of cells, the mesoderm, which, either by itself or in
combination with ectoderm and endoderm, gives rise to organs and
organ systems.
25
Parasitic Flatworms
Living at the expense of one’s neighbor is an old habit among animals. Practically all animals harbor one or
more kinds of parasites, and most of these are themselves host to even smaller parasites. Parasitism is a
relationship where one organism is harmed and the other organism benefits.
A well adapted parasite usually lives without causing serious harm to its host. A well adapted example is the
trypanosome which lives in the blood of African wild game with no apparent ill effect upon the game. The
fact that this parasite causes severe illness and finally death, when it gets into the blood of humans or our
domestic animals, is taken as an indication that the parasite has only relatively recently come into contact
with these hosts. Neither parasite nor host has had time to make proper adjustments. It does a parasite no
good to kill the very host it relies on for nourishment.
The tapeworms (class Cestoda) are usually long, flat, ribbon-like animals, some species of which live as
adults in the intestine of probably every species of vertebrate. The most common tapeworm of humans is the
so-called “beef tapeworm”. (Taenia saginata) It maintains its place in the intestine, despite the constant
flow of materials, by means of four suckers on the minute knob-like head called the scolex. Behind the
head is a short neck or growing region, from which a series of body segments called proglottids are
constantly budded off. The sections closest to the scolex are the younger ones; those farthest away are the
most mature. Thus the body widens gradually along its length, and the sections are in all stages of
development.
The body is covered externally by a protective cuticle, as in flukes. But unlike flukes, tapeworms have no
mouth and no trace of a digestive system. They live in the intestines of their host, where digested food
is readily available; there they simply “soak up” their nourishment… truly the laziest way of living.
REPRODUCTIVE SYSTEM
The reproductive system lies embedded in the mesoderm and is so highly developed in mature sections that
the tapeworm is sometimes described as
nothing but a reproductive factory. There is
a complete set of male and female organs in
each section. The male organs start to grow
first. They consist of numerous small testes,
which are connected by a single convoluted
sperm duct where sperm will exit out of a
modified penis. Running parallel with the
sperm duct is the vagina, a female duct
which receives sperm. Self-fertilization can
occur within the same segment, or crossfertilization can take place between the
segments of different worms when two or
more are present in the same
host. The most common method of sperm
26
transfer is from one section of the worm to a more mature segment farther down the length of the tapeworm.
This is possible when the animal is folded back on itself for part of its length. Eggs are produced in a pair of
ovaries and pass into the oviduct. Once the eggs are fertilized by the sperm, they pass forward into the
uterus, which at first is a single sac but later develops numerous branches. Eventually all the female
structures will degenerate except the uterus, which becomes enormously bloated with eggs undergoing
development into embryos. This ripe segment is said to be a “gravid” segment.
LIFE CYCLE
The life cycle of the beef tapeworm involves the eating habits of man and cow. The cow eats vegetation on
which human feces have been deposited. In the intestine of the cow the embryo, which is armed with six
sharp hooks, bores its way through the wall of the intestine and into a blood vessel. In the blood stream the
six-hooked embryo is carried to a muscle. It will remain there and grow into a bladder from which the
scolex of the worm develops. Eventually the head pokes out and attaches itself to the intestinal wall of its
host by means of suckers. Nourished by an abundant food supply, it soon grows a long body and produces
eggs.
The lifecycle of the pork tapeworm has a similar life history except that the bladders develop in pigs. It can
be dangerous as some bladderworms can develop in humans. If these settle in the muscles, no great harm
can occur. Sometimes, however, they lodge and grow in the eyeball, interfering with vision. Certain causes
of insanity or epilepsy are really due to bladderworms in the brain.
A very thin person is frequently accused of harboring a tapeworm, and it is true that infected individuals are
sometimes emaciated. The anemia and the nervous disorders that sometimes occur are not due as much to
loss of food as to the poisonous substances given off by the parasite. Also, the mere bulk of the worm,
especially when folded back on itself many times may block the intestine and produce serious temporary
illness.
The presence of a tapeworm can be detected by the appearance in the feces of the white, ripe sections loaded
with embryos. The only way to get rid of the parasite is to take by mouth some drug that kills the head and
causes it to detach from the intestinal wall, whereupon the whole worm is evacuated with the feces.
LIFE CYCLES
Many tapeworms have more than one intermediate host. The “broad fish tapeworm”, which may be 3
centimeters wide and 25 meters long, is the largest and the most injurious tapeworm that lives in humans.
The life-history requires that the eggs reach water, that the larvae, which hatch are eaten by small
crustaceans, and that the crustaceans are eaten by fish. Humans get the parasite when we eat raw or
imperfectly cooked fish.
Sometimes humans are the intermediate host for a tapeworm that lives its adult life in some other mammal.
Echinococcus granulosis is a minute tapeworm (with only three or four segments) that live as an adult in the
intestine of the dog and occurs only as a larva in humans. In spite of the small size of the adult, the larva is
enormous. Human infection results from drinking contaminated water or from allowing dogs to lick the face
and hands. Because of the unclean habits of dogs, their tongues are likely to carry tapeworm eggs.
27
The lowest grade of parasitism is that practiced by the flukes which live as external parasites attached to the
skin or gills of fish. These parasites have enormous suckers allowing them to hang on to a fast moving
object. The flukes which live as internal parasites, imbedded in the tissues or clinging to intestines have little
trouble hanging on; their suckers are not as elaborate as those of external parasites. But the problem of
getting their offspring established in a new host is a much more difficult one. It has been solved by
increasing the number of potential offspring and by complex life-cycles. All flukes that parasitize humans
are internal flukes.
The most important of these are the blood flukes or
shistosomas, elongated and slender flukes, which
differ from most in that they are not hermaphroditic
but occur as separate males and females. The sides of
the male fold over to form a groove in which the
longer and more slender female is held. The worms
live in the blood vessels of the intestine, clinging to the
walls of the vessels by means of suckers and feeding
on blood.
The female lays her eggs in the small blood vessels of
the intestine. As the blood vessels of the host become
congested with eggs, the walls of the vessels rupture,
the intestine breaks and the eggs are discharged into
the cavity of the intestines. From there, microscopic
eggs are carried out in the feces. If the feces were
removed by a modern sewage system or deposited in a
dry location, that would be the end of the young
shistosomas.
But in China and Japan where this parasite flourishes,
human feces are used to fertilize the soil. The feces is
deposited in irrigation ditches or water canals. This
provides the eggs with ready access to water where
they hatch.
A ciliated larva called the miracidium, emerges and swims about. If the miracidium does not encounter a
snail of a certain species, it perishes after about 24 hours. If it comes into contact with the right kind of snail,
it burrows into the soft body of the snail and feeds on the tissues. Meanwhile, the cilia are lost and the
miracidium is transformed into a sac, called a sporocyst, which produces a swimming bud called a
cercarias, which resemble the adults in several ways. They have two suckers, a forked digestive tube, and
an excretory system with flame cells. They make their way out of the snail and swim about near the surface
of the water, where they come in contact with the skin of a man who is bathing or wading. Millions of
Chinese and Japanese are infected during the planting of rice, as they stand barelegged in the shallow waters
of the rice fields. The cercaria attaches itself to the skin digests its way through the skin into a blood vessel.
It is carried in the blood stream to the blood vessels of the intestine. There the young fluke feeds and grows
into an adult worm, finally mating with another that entered at the same time or with one already
established from a previous infection.
The presence of schistosomas in humans causes a disease called schistosomiasis characterized by body pains,
a rash, and a cough in the early stages, severe dysentery (water loss) and anemia later on. Victims may live
for many years but gradually become weak and emaciated (skinny) and eventually die of exhaustion or
succumb to other diseases because of their weakened condition.
When a parasite lives for part of its life cycle in one kind of animal and spends another part of its life cycle in
another kind of animal, the host that harbors the sexually mature form is said to be the final host, and the
one that harbors the young stages is called the intermediate host. In the case of Schistosoma, man is the
final host, and a certain species of snail is the intermediate host.
28
A liver fluke that lives in man and illustrates a life-cycle involving two intermediate hosts is the Chinese liver
fluke, (clonorchis sinensis), of China, Japan, and Korea. The adult is about 2 cm long and has two
suckers. The outer cuticle is very thick and highly resistant to digestive juices. The fluke is hermaphroditic,
and the fertilized eggs pass from the liver into the intestine and out with the feces. If the feces get into water,
as they commonly do, the eggs do not hatch into free-swimming miracidia, as in most flukes, but are eaten
by snails. Within the digestive tract of the snail the egg opens, and the miracidium emerges and makes its
way through the wall of the digestive tract into the tissues of the snail. There it becomes transformed into a
sporocyst, which produces, instead of cercarias, another asexual form, the redia. The development of redias
further increases the number of young forms, for each redia subsequently produces many cercarias, which
escape from the snail and swim about. The cercarias encyst in the muscle of a fish, which thus serves as the
second intermediate host. They burrow through the skin of the fish, lose their tails, and secrete about
themselves protective capsules. The fish respond by forming an outer capsule around each parasite. There
they remain until the fish is eaten by the final host, which is us. In the human stomach the cysts are digested
out of the flesh, and in the intestine the capsule is weakened and the young fluke emerges. It makes its way
up the bile duct and into the smaller bile passages of the liver, where it attaches by its suckers and feeds on
blood. These flukes may persist for many years, causing serious anemia and disease of the liver from
blocking off the bile passages.
29
30
ANIMAL KINGDOM 2
NEMATODES AND ANNELIDS
23. State the advantages of having a coelom and a two opening digestive system.
PHYLUM ARTHROPODA
24. List the characteristics of this phylum.
25. Describe the characteristics of the following major groups of Arthropods:
Crustaceans, Spiders and their relatives, Insects and their relatives.
Give a member of each group.
26. Label diagrams of the internal and external anatomy of a crayfish.
27. Explain how a grasshopper is modified to carry out life activities.
28. Describe distinguishing characteristics of insects.
29. Explain the difference between incomplete and complete metamorphosis.
30. Explain or identify the following: chitin, tracheal tubes, spiracle, book lung,
malpighian tubule, ommatidium, molting, open circulatory system, sinuses,
gastric mill, green glands, chelicerae, pedipalps.
PHYLUM CHORDATA
31. List the characteristics of this phylum
32. Give the characteristics of the classes studied. These include fish,
amphibians, reptiles, birds and mammals.
33. Outline the pathway of blood in the mammalian system.
34. State the function of the following: red blood cells, white blood cells,
platelets, plasma
35. Describe the different types of hearts found in this phylum
36. Describe the path of blood in a human heart.
37. Label a diagram of the human digestive system. Explain what happens in
each part.
38. Diagram a nephron in a human kidney and explain how it works.
39. Diagram the respiratory system and explain how it works.
31
40. Diagram a human brain and identify the functions of the brain stem,
cerebrum, occipital lobe and cerebellum.
41. Dissect a rat to show the internal structures.
42. Label a diagram of the internal anatomy of a rat.
32
Phylum Arthropoda
text reference: 715-718
The Arthropods are considered to be the most successful phylum of organisms on
Earth. In terms of numbers alone, ¾ of a million species is the closest estimate,
which is more than three times the number of all other animal species combined!
This phylum includes animals adapted to living terrestrially (on land) such as
spiders, insects, centipedes and millipedes, and others adapted to living in water
such as crayfish, shrimp, and lobster.
All Arthropods have bodies that are ______________________ with a tough
outer ________________________ made from protein and a carbohydrate
called ____________________. Arthropods derive their name from the fact
that all Arthropods have ______________________________________.
Arthropods appeared on Earth more than 600 million years ago. You can
remember some of the earliest Arthropods as the Trilobites of which many are
found around the Cranbrook area. Throughout the evolution of arthropods,
fewer body segments and highly specialized appendages for feeding, movement
and other functions has resulted.
This trilobite which was common
around 500 million years ago,
had many appendages, a trend
that did not last.
Today’s
arthropods are much more varied
and specialized in their fewer
segments
and
sophisticated
appendages.
Arthropods use complex organ systems that help them carry out many of life’s
essential functions including feeding, respiration, circulation, excretion,
response, reproduction and movement.
33
Grasshoppers are arthropods with organs highly developed for surviving in dry
climates. Observe the tracheal tubes, spiracles, and the malpighian tubules in the
diagram below. Identify their functions:
Spiracle: _________________________________________________
_______________________________________________________
Tracheal tube: _____________________________________________
_______________________________________________________
Malpighian tubule: __________________________________________
________________________________________________________
Notice the other structures listed in the diagram. The grasshopper is well
equipped to carry out many of the “life activities” in an effective manner.
34
Copy the diagram of the grasshopper’s internal structures from the white board
Many arthropods go through a process of metamorphosis. You may be most
familiar with metamorphosis in insects. Insects undergo either incomplete or
complete metamorphosis.
Incomplete metamorphosis
Complete metamorphosis
35
Below is a summary of the versatility displayed by arthropods in a sample of
some of life’s activities:
The classification of arthropods is largely based on the number and structure of
their body segments and type of appendages present, particularly their
mouthparts.
The major groups of arthropods includes the:
Crustaceans, spiders and their relatives, and insects and their relatives.
Begin the chapter 28 questions assigned.
36
37
38
PHYLUM CHORDATA
Like all invertebrates you have studied, the vertebrates are animals too.
Vertebrates all have the same body plan whereas each invertebrate phylum may
be different.
All available evidence indicates that chordates have evolved from the
invertebrates, but it is impossible to establish the exact relationship.
Vertebrates belong to the phylum Chordata. As members of that phylum, they
have several characteristics that separate them from all other animals.
Major Characteristics:
1. Dorsal hollow nerve cord: this nerve usually runs the length of the body
only to enlarge at the anterior end to become a brain.
2. Notochord: this is a stiff skeletal rod which protects the nerve cord. This
structure may disappear later in life but is always present at some time in a
chordate. In us, the notochord becomes the bony vertebrate.
3. Pharyngeal pouches: these pouches look like gill slits and do indeed
become them in some chordates such as fish. In us however, the pouches
migrate downward to become part of the throat and ear.
4. Post Anal Tail: at some point in life (even the embryo stage) all chordates
have a post anal tail usually projecting beyond the anus.
5. Ventral Heart: this heart includes dorsal and ventral blood vessels in a
closed circulatory system.
6. Complete Digestive System.
7. Exoskeleton may be present
8. Endoskeleton present in the majority of members.
The generalized structure of a typical Chordate has the following:
39
Chordate Classes
1. Agnatha (jawless fishes)
-
their fins are not paired, eel-like body, no scales
sucker-like oral disc, jawless
ectotherms
2. Osteichthyes (bony fish)
-
fins are paired, scales present
swim bladder present
two chambered heart
stream-lined body
ectotherms
40
3. Chondrichthyes (Elasmobranchi) = sharks, skates, rays
-
endoskeleton is made entirely of cartilage
no swim bladder present
ectotherms
4. Amphibia (frogs, toads, salamanders)
-
paired limbs usually present
moist skin, no scales
ectotherms
three chambered heart
eggs without shells (fertilization in water)
41
42
5. Reptilia (snakes, turtles, lizards)
-
paired limbs
scales present
ectotherm
three to four chambered heart
eggs with shells (adapted to life on land)
As blood enters the heart, oxygen poor blood from the body and oxygen rich
blood from the lungs enter the single ventricle where they mix.
The “incomplete division” of the single ventricle found in the three chambered
heart diagram of the turtle causes oxygenated blood to mix with deoxygenated
blood. In more complex chordates this separation of the ventricle into two
chambers is complete, forever separating the oxygen rich blood from the oxygen
poor blood.
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6. Aves (birds)
-
paired limbs, usually adapted for flying, feathers are present
legs have scales, jaws have a beak
endotherm
4 chambered heart with complete separation (a septum)
eggs with shells
no urinary bladder and modified respiratory system (air sacs) to allow
continuous flow of air
Bird lungs work different…
Because flying is a high-energy activity, birds generally have a high metabolic rate
and require a great deal of oxygen. Thus, they have evolved a two-cycle breathing
process involving both lungs. Eight or nine extensions of the lungs (air sacs) act
as bellows that temporarily store air and then contract to force air through the
system. This moves fresh air through the lungs when birds are inhaling, and also
when they're exhaling.
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On inhalation, both sets of air sacs (the anterior and posterior air sacs) inflate at
different times. First, inhaled air flows down the trachea, bypasses the lungs, and
fills up the posterior air sacs (b). At the same time, the anterior air sacs fill with
stale air from the lungs (d).
On exhalation, both sets of air sacs deflate, forcing fresh air from the posterior
sacs into the lungs (c), and stale air from the anterior sacs out through the
trachea (e). Air takes two cycles of inhalation and exhalation to pass through the
system and out of the bird.
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7. Mammals
-
hair present
breast feed young milk
endotherms
4 chambered heart
Placentals: eggs develop in an internal uterus with placental attachment
Marsupials: bear live young, but at a very early developmental stage
Monotremes: lay eggs that hatch outside the body but feed young milk
The platypus is an obvious representative of the “odd” features present in a
monotreme. It has features representative of reptiles, birds, and mammals.
46