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Invertebrates in Animal Unit
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Animals WithoutBackbones: The
Invertebrates
The InvertebratesIn the laboratory investigation, you ob
served a variety of animals that are all knownas invertebrates. This group has many different types of animals in it, and many of itsmembers do not at first even appear to be animals. However, the greatest variety and larg^est number of animals alive on earth today areclassified as invertebrates. In spite of theirgreat variety, these animals are grouped together because all of them lack an internalbackbone.
SPONGES:PHYLUM PORIFERANSCharacteristics. Some sponges inhabit freshwater, but most species of sponges live in theocean. All sponges are composedof many cellsthat are arranged in two main layers arounda hollow cavity (Fig. 7-1). The cell layers arepierced by thousands of pores, hence the nameporiferans, or porebearers. Imbedded amongthe .cells is a tough supporting material thatforms the skeleton of the "sponge. Somesponges have a hard skeleton composed oflime, while others are of glasslike silica; athird type of sponge has a tough but flexibleskeleton composed of spongin^Aduh spongesdo not move around; they grow attached^tosolid underwater objects. Sponges can reproduce asexually by forming a bud, which is asmall bulge that breaks off to become a newsponge. Sponges can also reproduce sexually,by forming sperm and egg cells.
Vase-Shaped Sponge. The attached (bottom)end of the sponge is closed; the unattached endis open. Certain cells of the inner layer bearwhiplike hairs similar to cilia. The beating ofthese hairs causes a current of water to flowinto the pores, to the hollow cavity, and outthrough the open end of the sponge. Some cellsof the inner layer engulf microscopic food particles from the water and digest them. All theceils absorb dissolved oxygen and release carbon dioxide. The current of water carrieswastes ou t through the open end of the sponge.
Open end.
-Pores
v—Path of water
^.Hollow cavity
\ * •« < «• /_x**""• "i*r
> \) * * ■* ( Young sponge(bud)
^—-£—>»! .-____*• i *■—
- . '••"' ■'•• ..■"•;.!■ -■: - • <-v. ■ ;• .. ■• :•-__-
Fig. 7-1. Sponge (partly cutaway view).
Importance of Sponges. When sponges arebrought to the surface by sponge divers, andplaced in the air to dry out, the living cells dieand rot. The tough supporting material remains. When washed and dried, these sponginskeletons become the "natural sponges" usedfor bathing. Living sponges are an importantpart of coral reef communities.
JELLYFISH, HYDRA, CORALS:PHYLUM COELENTERATESCharacteristics. This phylum comprises alarge group of simple animals that includesthe jellyfish, hydra, corals, and sea anemones(Fig. 7-2). A few species of this phylum inhabitfresh water; most live in salt water. Like thesponges, the coelenterates are many-celiedand are composed of two main cell layers. Allcoelenterates have a layer of jellylike materialbetween the two cell layers. Coelenterates lackhard internal body parts, and are either bell-shaped Or vase-shaped. Musclelike cells, nervecells, and stinging cells are found in thisgroup.
Sea anemone
-Limestone skeleton
Coral (enlarged)
Fig. 7-2. Examples of coelenterates.
All members of the coelenterate group havemouths surrounded by long flexible arms,called tentacles. These tentacles have stingingcells for capturing prey. The mouth leads directly into a central, hollow digestive cavity.In fact, the name coelenterate means "hollowgut." The jellyfish and hydra are delicate andtransparent. Their bodies consist of about 95%water. Some jellyfish and hydra reproduce byforming buds. Others form sperm and egg cellsto reproduce sexually. The sea anemone lookslike ajarge hydra and is often colorful, resembling a flower. Coral animals are soft and tiny;but each animal secretes a hard limestoneskeleton around itself. As a coral animal reproduces by budding, the new individuals remain attached to the parent, forming a colony.Colonies made up of millions of attached limestone skeletons form coral reefs.
Hydra. Like the sponge, the hydra is usuallyattached to an underwater object. It is closedat the attached end (foot) and open at the otherend (mouth). A hydra can extend itself to alength of about 1 cm. When disturbed, it contracts into a tiny ball. The hydra, unlike thesponge, can move from place to place byslowly sliding along on its base, or foot. Sometimes it inverts itself, turning its foot upward.It then moves along on its arms or in very slowsomersaults. Its musclelikc cells make thesemovements possible.
The hydra captures food by means of itsarms, which sting the prey and then push itthrough the mouth into the digestive cavity.Here, special cells of the inner layer secreteenzymes and digest the food. Solid wastes aredischarged through the mouth. Since everycell of the animal is close to water, each cellcan take in oxygen directly from the water bydiffusion and. similarly, can excrete liquidwastes directly into the water.
By means of a network of nerve cells, thehydra receives stimuli and responds to themby muscular action or by discharging its stinging cells. When stimulated, the stinging cellsshoot out hooked, poisonous threads that canentangle and paralyze very small animals. Inthis manner, the hydra protects itself againstenemies and captures animals smaller than itself for food.
Importance of Coelenterates. Large jelly-fishes, with poisonous stinging cells in theirtentacles, endanger swimmers who are stungby them. Corals are important because accumulations of their skeletons form underwaterreefs. When ships run into such reefs, both theship and the reef may be damaged. Large col-
2.
wall of the new human host. There they develop into adult tapeworms, capable of reproduction.
Liver fluke. This flatworm is a parasite thatinhabits the liver of such hosts as humans andsheep. Flukes may reach a length of about 2cm. and a width of about 1 cm. The fluke(which has a sucker, but no mouth) attachesto. the host's liver, and feeds upon its blood.The fluke produces eggs that reach the intestine of the host by way of the bile duct andleave the host's body with solid wastes. If theeggs are swallowed by a certain kind of snail,they hatch within the snail. The young flukesthen leave the body of the snail and enter thebody of certain fishes. When people eat suchfish uncooked, the young flukes pass into theirlivers, where they grow into adult flukes.
Importance of Flatworms. Tapeworms andliver flukes cause serious diseases in theirhosts, leading to physical weakness and, sometimes, death. These diseases are easily prevented by thoroughly cooking all red meat andfish until heat has penetrated the food. Wormparasites cannot withstand teinperaturesabove boiling for more than about 20 minutes.Better sanitation of water supplies in. developing nations can also help cut down flat-worm infections in people.
ROUNDWORMS:PHYLUM NEMATODESCharacteristics. Some species .of roundworms live in soil; some live in water; someare parasites of animals; others are parasitesof plants. Most free-living roundworms arevery small; the parasitic roundworms can beover a meter long. The body of a nematode isslender, rodlike in shape, soft, and also composed of three layers of cells. The middle layerof cells encloses a body cavity. Tissues andsimple organ systems are present. Roundworms, which are pointed at both the headand tail ends, possess a mouth and an anus.Among the most important roundworms arethe hookworm and the trichina worm (Fig. 7-4). Other examples of roundworms are thethreadworm and the pinworm.
Hookworm. Adult hookworms, less than 2cm. long, are often found attached to the intestinal wall of humans who live in warm regions. The worms feed upon the host's blood,causing the person to feel weak. The eggs of
Hookworm (about twice natural sirs]
Trichina worm in muscle tissue(microscopic view)
Fig. 7-4. Examples of roundworms.
the hookworm pass out of the host's body withthe solid wastes. If these eggs reach moist soil,they hatch into young hookworms. Theseworms can enter the body of a new host byboring through the skin of the feet. The wormthen enters the blood and is carried to thelungs or another organ. Eventually, the wormarrives in the intestine, fastens itself to the intestinal wall, and bores into a blood vesselthere. Feeding on blood, the hookworm growsto adulthood and reproduces. Hookwormsalso infect the intestines of dogs, cats, andhorses.
Trichina Worm. This tiny (1/2 cm.) worm isa parasite in the human, the pig, and the rat.Pigs that eat rats infected with the trichinaworm become infected themselves. The youngtrichina worms burrow into the pig's musclesand,Tike tapeworms, lie inactive there insidecysts. If a human eats infected pork that hasnot been thoroughly cooked, the worms leavethe cysts, enter the person's small intestine,mature and reproduce. The new generation ofyoung worms then enters the muscles of thesame human to form more cysts, causing intense muscular pain.
Importance of Roundworms. Hookworm disease results in a loss of blood and general bodyweakness. In this condition, a person is likelyto catch other diseases. Hookworm diseasecan be prevented by the Sanitary disposal of
human wastes and by wearing shoes in ruralareas. Trichinosis, the disease caused by thetrichina worm, is not only painful but may, ifuntreated, cause death. This disease can beprevented by cooking pork and other meatslong enough and at temperatures high enoughto kill the parasites that may be present. Someof the parasitic roundworms also destroy tomatoes and other crops by sucking out the sapfrom their roots.
SEGMENTED WORMS:PHYLUM ANNELIDSCharacteristics. Some segmented wormslive in fresh water, but most live in salt water.A few others live on land. The body of theseworms is long and tubelike in form. Unlike thesurface of roundworms, which is smooth, thesurface of these worms is divided into manysections, or segments. Like the two otherworm phyla and, in fact, like all higher animalphyla, segmented worms, or annelids, havethree layers of cells.
The organ systems are complex. The foodtube extends from mouth to anus, having specialized regions, such as an intestine, betweenthese openings. A complete circulatory systemis present. It is made up of arteries, capillaries,and veins. The nervous system is composed ofa solid mass of nerve tissue in the head region(a "brain") and a solid nerve cord that runsalong the lower side of the body. Althoughsome segmented worms reproduce by splitting in half, all are capable of sexual reproduction. Every earthworm has both male andfemale reproductive organs. The clitellum isthe body segment that plays a role in theearthworm's mating process. Examples of segmented worms are sandworms, leeches, gianttube worms, and earthworms. The earthwormis the one most familiar to people (see Fig. 7-5).
Earthworm. The earthworm lives in moistsoil. This worm burrows into the soil by eatingit and the organic matter that it contains. Asthe soil passes through the worm's food tube,the organic matter is digested and absorbed.The remaining waste material is dischargedthrough the anus.
The circulatory system of the earthwormconsists of two major blood vessels—an arterythat runs above the food tube and a vein thatlies below the food tube. About 2 1/2 cm. behind the front end of the worm, these bloodvessels are joined by five pairs of more muscular blood vessels (the "hearts"). These fivepairs of hearts continually pump blood. Elsewhere in the body, branches from the arteryjoin the vein by way of capillaries. The wormtakes in oxygen and gives off carbon dioxidethrough its moist skin.
The earthworm responds to stimuli bymeans of reflex actions that are controlled byits nervous system. (You will learn about reflexes in Ch. 20.)
Importance of Segmented Worms, Segmented worms serve as food for many animals. The earthworm is probably mostimportant to people, because this worm'sactivities make farming possible. As earthworms burrow, they aerate the soil, bring deepsoil to the surface, and enrich the soil withtheir wastes. Earthworms arid sandworms arefrequently used as bait in fishing. The leech(or bloodsucker), which is a temporary parasite on humans, turtles, and fish, is also important to people. Because the leech's salivacontains a substance that prevents blood.clotting, leeches are now being used to aid bloodflow and healing in some types of surgery.
HARD-SHELLED ANIMALS:PHYLUM MOLLUSKS
Clitellum
"Brain" "He3/lS" Art.ef*
Mouth Nerve cord Vein Food tube Se*men"
Fig. 7-5. Earthworm (partly cutaway view).
Characteristics. There are over 100,000 species of mollusks, divided into three distinctclasses based on their shells. Some animals inthis group live in salt water; some live infreshwater; and others live on land. The body of allmollusks is soft and enclosed by a soft tissuecalled the mantle. The outer side of the mantleproduces a hard shell material. Some of theanimals in this phylum, like the snail, have asingle coiled shell; others, like the clam andoyster, have two shells connected by a muscular hinge; and a few, such as the squid, havea shell that is not visible because it is small
S
Snail Octopus
Fig. 7-6. Examples of mollusks.
Scallop
and imbedded in the soft tissues. (The octopushas no shell at all.) Clams and snails move bymeans of a muscular foot. Squids and octopuses move by squirting jets of water. See Fig.7-6 for some examples of common mollusks.Clam. Many kinds of clams burrow in sandin shallow water. The central mass of theclam's body contains all the major organ systems (see Fig. 7-7). Muscles open and close theshells of the clam. Folds of the mantle formtwo passageways through which water flowsin and out. and passes over the gilb. The flowing water brings in oxygen and food. The ox*ygen is taken up by blood inside the gills. Thefood, which consists of microscopic organisms, is directed to the animal's mouth bycilia.
Hinge of shell
Mouth
Muscleof shell
Kidney
Anus
Nervoussystem
Edge ofmantle
Reproductiveg l a n d I n t e s t i n e .
Fig. 7-7. Cutaway view of a clam.
Importance of Mollusks. Among the mollusks that are used as food by people and-otheranimals are oysters, clams, snails, octopuses.
and squids. Some freshwater and saltwaterclams and oysters produce pearls when particles of sand become lodged between themantle and the shell. The shells of some mollusks are used to make buttons, jewelry,-andeven money. Animals of this group that areharmful include the "shipworm" (which boresthrough the wood of ships and piers), snailsthat transmit parasitic diseases; and snailsand slugs that feed on our crops.
SPINY-SKINNED ANIMALS:PHYLUM ECHINODERMSCharacteristics. There are over 5000 different kinds of echinoderms. All the animals inthis group live in the ocean. Most echinodermshave a bodyshape that either resembles a staror is round. The body is covered with numerous sharp projections, called spines, hence thename echinoderm, which means "spinyskinned." Echinoderms have no head; butthey do.have a mouth. These animals have special organs of locomotion, called tube feet. Allof the major organ systems are present. Common examples of echinoderms are the starfish,sea urchin, brittle star, sea lily, and sea cucumber (Fig. 7-8).
Starfish. The starfish lives in shallow offshore water. Its body consists of five arms, orrays, that extend from a central disc. The un-dersurfa.ee of each arm bears hundreds of tubefeet lined up in a groove. The tube feet are usednot only in locomotion, but in capturing andfeeding upon such animals as oysters andclams. The starfish wraps its arms around aclam and attaches its tube feet to the shells ofthe clam. By exerting a steady, strong pullupon the shells, the starfish tires the clamuntil the mollusk relaxes its muscles andopens its shells. Then, the starfish pushes itsstomach out of its small mouth and into the
6
space between the clam's shells. Before it ispulled back into the starfish's body, the stomach digests the soft parts of the clam.
Importance of Echinoderms. In some Asiancountries, sea cucumbers are used as food.Certain sea urchins have poisonous spines,which are very painful if stepped on. Starfishoften damage and destroy clams and oystersthat are being cultivated for market. Somestarfish also destroy coral reefs. However, scientists find starfish very interesting becausestarfish can grow back lost body parts, suchas an arm.
ycucumber
Slarfifih
Sea lily
Seaurchin
Fig. 7-8. Examples of echinoderms.
JOINTED ANIMALS:PHYLUM ARTHROPODSCharacteristics: All arthropods have bodiesthat are divided into either two or three sections and are covered by an outer shell, or exoskeleton. Hingelike joints between the bodv
sections give the animals flexibility. Even thelegs and antennae (feelers) of these animals arejointed. In fact, the name arthropod means"jointed feet." The organ systems are complexand well developed. The hard exoskeleton thatcovers an arthropod does not grow along withthe animal. In a process called molting, theexoskeleton is shed. Then, the animal growsrapidly until a new hard exoskeleton forms.
There are more kinds of arthropods thanthere are of all other species of animalscounted together. The four major classes ofjointed animals are axistaceans, myriapods,arachnids, and insects.
Class I: Crustaceans. Examples of this classare the lobster, the shrimp, and the crab (Fig.7-9). There are over 25,000 species of crustaceans. These animals usually have two bodysections containing two pairs of antennae andfive pairs of legs. Crustaceans are mainlyaquatic and they breathe by means of gills.Many animals in this group are prized as foodby people all over the world. Crustaceans suchas krill (a shrimp) are an important- foodsource for whales, too.
Crab
Lobster
Fig. 7-9. Examples of crustaceans.
Clas
s II:
Myr
iapo
ds.
Milli
pede
s an
d ce
nti
pede
s (F
ig. 7
-10)
are
the
main
exa
mple
s of
this
class
. M
yria
pods
(m
eani
ng "
a gr
eat
man
yfe
et")
live
in th
e gr
ound
, usu
ally
in d
ark,
moi
stpl
aces
. Milli
pede
s (m
eani
ng "
thou
sand
feet
")ha
ve tw
o pa
irs o
f leg
s on
eac
h bo
dy s
egm
ent;
cent
iped
es (m
eani
ng "h
undr
ed fe
et")
have
one
pair
of le
gs p
er b
ody
segm
ent.
Som
e ce
nti
pede
s ar
e be
nefic
ial—
they
eat
inse
ct p
ests
.O
ther
cen
tiped
es a
re h
arm
ful—
thei
r po
ison
ous
bite
is p
ainf
ul to
hum
ans.
Milli
pede
s ea
tde
cayin
g pl
ants
.
yvTT
TrCe
ntipe
de
Millip
ede
Fig,
7-1
0. M
yriap
ods.
Clas
s III
: Ara
chni
ds. E
xam
ples
of t
he a
rach
nids
are
spi
ders
, sco
rpio
ns, t
icks,
and
mite
s.(S
ee F
ig. 7
-11.
) The
se a
nim
als
have
two
body
sect
ions
and
fou
r pa
irs o
f wa
lking
legs
at--
tach
ed to
thei
r fro
nt b
ody
sect
ion.
The
re a
reov
er 1
00,0
00 sp
ecies
of a
rach
nids.
Gar
den
spi*
ders
, whi
ch e
at in
sect
s, a
re u
sefu
l to
us. T
hesc
orpi
on,
which
has
a p
oiso
nous
stin
g, i
sha
rmfu
l to
hum
ans.
Also
har
mfu
l are
som
etic
ks a
nd m
ites,
whi
ch f
requ
ently
car
ry d
isea
ses.
Spi
ders
are
wel
l-kno
wn fo
r the
var
iety
of in
trica
te w
ebs
they
wea
ve to
cat
ch p
rey.
Spide
r
Kb
Scor
pion
Fig.
7-
11.
Arac
hnid
s.
Tick
Clas
s IV
: Ins
ects
. Mos
t ins
ects
hav
e th
ree
body
sec
tions
, or r
egio
ns, w
ith th
ree
pairs
of
legs
and
two
pairs
of w
ings
, whi
ch m
ay b
e un
equa
l in si
ze. T
here
are
mor
e th
an 6
00,0
00 d
iffe
rent
spec
ies o
f inse
cts. I
nclud
ed a
mon
g th
ese
are
the
wasp
, dam
selfly
. aph
id, a
nt, s
ilver
fish.
pota
to b
eetle
, and
gra
ssho
pper
. See
Fig.
7-12
for
som
e ex
ample
s.
Aphid
Fig.
7-1
2. E
xam
ples
of
inse
cts.
J1 Potat
o be
etle
Gra
ssho
pper
. The
hea
d of
a g
rass
hopp
er (F
ig.
7-13
) bea
rs tw
o la
rge
com
poun
d ey
es, w
hich
dete
ct m
ovin
g ob
ject
s. E
ach
com
poun
d ey
eco
nsist
s of
thou
sand
s of
tiny
eyes
. Also
pre
sent
Sim
ple
Com
poun
d H
eari
ey
e e
ye
Fron
t win
g
Ant
enna
/
Walk
ingleg
Spi
racl
es
Hin
d w
ing
Hea
d M
idre
gion
H
ind
regi
on
Fig.
7-
13.
Gra
ssho
pper
.
2
Asexual KeproductionThe Invertebrates o
REGENERATIONRegeneration is the process by which an or
ganism grows back a part of its body thai hasbeen lost. In plants, regeneration is often thesame as vegetative reproduction because complete plants are formed. In animals, regeneration also occurs, but lo a limited extent.Hardly any animals reproduce naturally byregeneration. Planaria worms can reproducethis way, either when cut in half or when theysplit in'half lengthwise (see Fig. 9-11).
Fig. 9-12. Regeneration in a starfish. ■
tebrates have a greater ability than vertebrates to regenerate lost parts. Very few vertebrates can regenerate lost parts.
BENEFITS OF ASEXUALREPRODUCTION
Asexual reproduction benefits organismsand people for the following reasons:
[j^OUspringParent
Fig. 9-5. Budding In hydra.
Budding In Hydra. A small swelling whichbecomes the bud, forms on the body below thearms of the hydra (Fig. 9-5). The bud consistsof numerous cells. As the bud matures, it develops a moulh and small arms. In time, thebud becomes detached from the parent hydraand grows lo adull size.
Fig. 9-11. Reproduction by regeneration—aplanaria splitting.
Some animals have greal powers of regeneration, others very little. Tadpoles can re-grow a'lost tail or leg. If a starfish is choppedinto five equal parts, each arm can grow intoa new starfish, as long as it is attached to partof the cenlral disk (Fig. 9-12). A lobster alsocan regrow a leg that has been broken off, butthe leg cannot regrow the rest of a lobster. Thehuman body can repair small surface injuries,but cannot grow back a limb that has been cutoff or surgically removed. In general, inver-
1. One parent can produce new organisms.This is especially beneficial when it is hardfor an organism to locate a mate.
2. All the new organisms have the same characteristics as the parent variety. This is ofvalue when people want to produce manyplants of a particular breed.
3. Offspring are produced more rapidly bythis type of reproduction than by sexualmethods. An example of this would be yeastand bacterial colonies.
4. Offspring can be produced from seedlessvarieties of plants through grafting. This isa very desirable trait in many food plants.
Animals WithoutBackbones: The
Matching QuestionsO n * , b t a n k U n e . , * , t h e ! e t t f h e , f c fl ^ & ^
fo tfie zrem !n column A.
f t C o l u m n A* £ - > C o l u m n B1. related to hydra
a d . c r a b- J - 2 . h a s r i b b o n l i k e s h a p e b . c e n t i p e d e1 - 3 . p o r e b e a r e r _ r 5 £ r T ^l b - 4 . a t y p e o f r o u n d w o r m ^ _ _ 1 _ _ _ ^
| c - u / • g t a s s h o p p s r -_ 3 . h a s s p i n e s a n d t u b e f e e t _■ f l a t w o r m -6 . h a s fi v e p a i r s o f , " h e a r t s " T r - s p e * g _
■-T
^ 7 . h a s fi v e p a i r s o f w a l k i n g , e g s ' ' r S L -L_ 8. has four pairs of walking legs
9. has a double shell and gills10. has three pairs of legs and four wings
,1
Multiple-Choice Questions° " * b i a n k " M ' ^ ^ ! S ^ *■ - ~ *
2-Sponges can reproduce asexually by£3- forming a bud
* . s p l i t t i n g i n h a l f * p r o d u c i n g s p o r e sa. releasing seeds3 r r ^ w i c i ' s * ? s * — - - * * .■« .
4. An animal that has stinging ceils is the« • s p o n g e A . s t a r f i s h ( Q u f y f f e h d . t a p e w o r m c
* S o f t - b o d i a d . r i b b o n l i k e a n i m a t e c l a s s i fi e d a s " ~a . r o u n d w o r m s b . j e l . y fi s h < T 5 fl a t w o r m s d . s e a f o o d . C
6 - T h e l i v e r fl u k e J e e d s u p o n '
- i n t e s t i n e ^ * ) b l o o d c . d e c a y e d m e a t d . w a t e r p l a n t s fi U
8 ( g ^ l T T. t f r t - , ^ . t t e t h e h U - n ^
3___
/ /
9. A worm that lives inside human muscle tissue is thea. tapeworm b. fluke (fjtrichina d. hookworm
10. Thorough cooking of pork can help prevent infection bva m a l a r i a a n d t r i c h i n a © h o o k w o r m a n d t a p e w o r mb. tr ichina and tapeworm _. tapeworm and malaria
11. The number of cell layers in a segmented worm isa. two {j^Jhrce c. four d. six
12. Examples of segmented worms include thea. earthworm, tapeworm, liver fluke (Qarthworm. sandworm. leechb. earthworm, sandworm, tapeworm d. sandworm. leech, hookworm
13^e circulaiory system of the earthworm includes\ajarteries, veins, and capillaries ' c. onlv capillariesb. only arteries and veins d. only veins and capillaries
.14. Which, worm normally lives ajl its life in moisi soil?a. tapeworm b. pinworm Qearthworm d. hookworm
15. Inrespiration, the earthworm takes in oxvsen throush its/ a. *kin b. gills c. lungs d. air tubes
16^-fhe animaLmost closely related to the ciam is thea. starfishr&Anail c. trichina d. shrimp
17. The body ofmollusks is covered witha-scal.es b. spines (g) a mantle d. hinged joints
18. The body of a starfish is covered withM h a r p s p i n c s . c . t o u g h s c a l e s
" A s h 0 ^ c l l i a _ * • a s m o o i h s h e l l19. The echinoderms cany out locomotion bv means of
a. tentacles b. pseudopods c. small tails (^)ubc feet20. Which ani-mal possesses an exoskeleton with joints'
a. snail Q^obster c. earthworm" </. coral21. The process of moltins refers to
• £a i reac t ion to .warmth c . a wav o f reproduc in2
^shedding a body covering _. use of slinging celJs22. Crustaceans, such as ihe shrimp, breathe bv means of• a. air tubes b. iisskin (cTkiUs d. lungs"
23'/?V a^imal m°St pl0Sdy rdaied t0 the sc°rp«on is the(tayspider £. sea urchin c. octopus d. starfish
24. The grasshopper breathes throush itsa. lungs (£)spiracies c. gills ~tf. mouth
25. The two shells of clams and oysters are connected bvW a m u s c u l a r h i n g e c . s p e c i a l j o i n t sb . a n e x o s k e l e t o n d m o v e r l a p p i n g s c a l e s
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Mo clified True-False Questionsof the following statements, the italicized term makes the statement incorrect.i incorrect statement, write the term that must be substituted for the italicizedtake the statement correct. For each correct statement, write the word true.
'mals with many pores and a central hollow cavity are known as' poriferans.
I capturing its food, a-jellyfish uses its tentacles.
Hvdra can reproduce by forming little spores.Animals whose skeletons form reefs are known as sponges.
- The tapeworm is a type of flatworm that is a host.
6 Hookworms and trichina worms are two types of flatwonns.
7 An annelid's body is divided into many segments.8. An octopus is a type of arthropod.
9. Segmented arthropods having many legs are called myriapods.10. Most insects have wings and four body sections.
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. Testing Your Knowledge1. Explain each of the following true statements:
a . A t v p e o f c o e l e n t e r a t e c a n w r e c k a s h i p . r - o _ £ < 4 - 1 . L l \ ^ r ,f e c _ _ _ _ _ _ ± ^ _ _ _ _ j _ _ : '■ " * * * * ^ ^
dawt c|ajC % V\. p c.b . T a p e w o r m d i s e a s e c a n b e p r e v e n t e d i n t h e k i t c h e n . :
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c. A starfish uses its tube feet for feeding as well as for moving.- T l * . . ^ . U S c t v % C c i . f t . - K . r v o w - « r f - H ^ V v a ^ ^ - r - r - v a o% r
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2 . W h y i s h o o k w o r m d i s e a s e r a r e a m o n g p e o p l e l i v i n g i n c i t i e s ? {
_ 3 < y S c o ^ v x o * U o V c k b < L c a ^ ^ ^ ! _ " V - ^ . ° ( M - . ^ / v ]3. Why wi l l a grasshopper not drown, i f only i ts head is below water? - j
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4 . W h y i s t h e s p i d e r c l a « i T . _ w . i• CZ ̂ ̂ cU™ a-2achnid and noc an 'nfctcti
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in the blank space at the^'ht ^ d°eS not bel°ng «'ith the others. Write that term« • e a r t h w o r m , h o o k w o r m , t r i c h i n a w o r m , p i n w - o r m « . * r W ^6 . l e e c h , s a n d w o r m . e a r t h w o r m , t a p e w o r m " ^ ^ ^f t o y s t e r , s t a r f i s h , s n a i l , s q u i d " / ' ■ 'd - w a s p , b e e t l e , s c o r p i o n , b u t t e r fl y ~e - s e a U r c h i n ^ b r i t t l e s t a r , c o r a l , s e a l i l y : " " T ^ S S ^
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