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CrayFrshDissection 07.05.
DISSECTION
OF THE CRAYFISH
Name
PartnerName
Hour
PhylumArthropoda ClassCrustacea
INTRODUCTION:
Crayfish(or "crawdads"or crawfishasthey aresometimescalled)
arefreshwatercrustaceansthat arevery similarto lobsters. You can
readilyfind thesein freshwater pondsandstreams in muchof the
United States.Watchfor their chimneylike mud mounds in the
shallowwaters.If you try to catchthem,you will soondiscover their
amazingability to makea hastyretreat-backwards!
Give two altemate"local" namesfor the cravfish:
The crayfishis an extraordinary exampleof the arthropod
characteristicofjointed legs.The crayfishhastwentypairsof
appendagesthat havebeenmodifiedfor specificfunctions. In this investigationyou will locateandexamine
the main externalstructuresandrespiratory systemof the crayfish.
Namethe phylumto which the crayfishbelongs:
Statethe majorcharacteristicof members of this phylum:
How manypairsof appendages doesthe crayfishhive?
The groupof organisms to which the crayfishbelongsis the largestof theplant andanimalphyla.Indeed, of
the millions of known species of animals,three-fourthsarearthropods. In additionto crayfish,this group
containsmillipedes,centipedes, spiders,scorpions,horseshoe crabs,insects,anda little knownanimal
calledPeripatuswhich is considered to be the "missinglink" betweenthe annelids(segmented worms)and
the arthropods.
The crayfishis a cannibalistic scavengerthat lives on themuddybottomsof streamsandponds.It emerges
at night to feedon deadanddecaying matter,insectlarvae,andworms.
Tell whatportionof all knownspecies of animalsarearthropods:
To what class doesthe crayfish belong? Name six other "common classes"that
belongto the phylumArthropoda:
What doesthe phrase "cannibalisticscavenger"mean?
Hereis a sunmaryof the phylumArthropoda.Useyour pencilto circlethe subphylum(mostbiologistscall
it a class)to whichthe crayfishbelongs.....
5u
ffi
h0ft6sndc cf'tib
centipede
rrniltipede
&cnocquitoet
rnot
all hsect
ordor rhown
As an arthropod,the crayfishhasa body protectedby a hardexoskeletonmadeof chitin.Periodicallv,the
crayfishsheds,or molts,its outerskeletonandgrowsa new one.After molting,the crayfishtakesin large
amountsof waterto increaseits body sizebeforethe new skeletonhardens.The crayfishbodyhasfive pairs
ofjointed legsandtwo segments, a fusedcephalothorax,andajointed abdomen.The carapace,apart of the
exoskeleton,coversthe cephalothorax.Crayfishbreatheby meansof gills. Tubularstructures,calledgreen
glands,removeexcesswaterandwastesfrom theblood.The "brain"
of the crayfishconsistsof a pair of
gangliaconnected to a ventralnervecord.
What is an exoskeleton?
of in the crustacean?
Describehow the cravfishincreasesin sizeaftera molt:
Name the organscrayfish use for breathing:.
Whatis the exoskeletonmade
When a crayfish shedshis exoskeleton,the processis called
z
Tell what greenglands do:
Crayfish are grouped in the phylum Arthropoda, which also includes such animals as insectsand spiders.
Arthropods are chancterizedby having
jointed appendages and segmentedbodies. In crayfish and other
higher arthropodseach appendagehas a specific function. Crayfish, which are aquatic,use their appendages
for swimming, walking, food-getting, reproduction, biting, touching, and tasting.
What doesaquaticmean? terrestrial?
Line a dissecting
panwith newsprint andplacea crayfishin thepanwith its dorsal(back)sideup. Feelthe
hardexoskeleton.It is madeof a substancecalledchitin.
Body Segments:The crayfish'sbody is dividedinto two majorregions:the abdomenandthe cephalothorax,
which includesthe headandthorax(chest).The cephalothorax
is covered by a pieceof exoskeletoncalled
the carapace.Note the curvedcervicalgroovethat marksthe division
betweenthe headandthorax.The pointedanteriorendof the carapaceis therostrum.Beneathit arethe
stalkedcompoundeyes.
The segmentedabdomenendsin a segment calledthe telson.Unlike the cephalothorax,the abdomencanbe
flexed.
Namethe two partsof the cephalothorax:
What do humanshavein placeof the cervicalgroove?
What canthe crayfishdo with the abdomenthat it cannotdo with the cephalothorax?
How manysegmentsdoesthe abdomenhave?
On the diagram of the dorsal surfacebelow, label the cephalothorax,abdomen,carapace,cervical groove,
rostrum, eyes,and telson.
Tag each of the following on your specimen: dorsal surface,cephalothorax,abdomen,carapace,cervical
groove, telson
Verified
I
Appendages:Turn the crayfishoverto exposeits ventralside.Note the manypairedappendages. Crayfish
havethe ability to regeneratelost bodyparts,soyou may find an appendagethat hasonly partiallyregrown.
Protrudingfrom the headaretwo long antennae. Two shorterbranchedantennulesare locatedbetweenthe
antennae.The crayfishusesthesestructuresfor taste, touch,andsmell.
Locatethe mouthopening.Surroundingthe moutharejagged
jaws calledmandibles,
usedfor biting and
chewing. Posteriorto the mandiblesaretwo pairsof maxillaeandthreepairsof leg-likemaxillipeds;these
structures areusedto hold food.Usea handlensto examinethesemouthparts.If you havetroubleidentiff-
ing them,referto the diagramsbelow.
Tag each of the following: venfral surface,antennae,
antennules.mouth
Verified
Usethe diagramsbelowandthe descriptionaboveto locatethe
variousappendagesthat surroundthe mouth. Working from
themouth"out" locatethe mandibles,maxilla,andmaxillipeds.
SECOND MAXILLA
THIID MAXILUPED
FINST MAXILLIPED
Tag each of the following: Maxilliped, maxilla, mandible Verified
s
V E N T R A LV I E W
O F H E A D
Third
MANDIBLE ORJAV FIRSTMAXILLA
Fcding appcndrg* ofa
Observethe abdominalregionandits divisioninto six segments. Thejointed appendages,called
swimmerets,on the first five segments alsoaid
in respiration by movingwateroverthe
gills. Grabthe edge
of the carapaceon onesideor the otherof the crayfishandlife it gently....thegills arelocated underthe
carapace.The carapaceis actuallynot "glued-down"to mostof the cephalothorax
At the
posteriorend,on eachsideof the telson,aremodifiedswimmeretscalleduropods.Theuropodsand
telson form a tail fin that is usedto propel the crayfishbackwardthroughthe water.
On the diagramof the ventralsurfacebelow,labelthe antennae,antennules,chelipeds,walking legs,
swimmerets,anduropods.
Tag eachof the following: walking legs,cheliped,swimmerets,uropod,gills.
Verified
1
Baseduponyour observationsandreadingto this point, complete-the"fi.rnction"columnin thetablebelow.
Then,carefullyremoveonesample of eachappendage(usescissorsandcut closeto thebody) andplaceit
in the samplecolumn. DO NOT TAPE THEM DOWN. Only ONE partnerwill needto havethe sample
appendagesin place....
Appendage Chan
Body Soction Appcndago Function
Caphalothorax Antennules
(1 pair)
AntennEe
{l pair)
Eyes
{compound,
1 pair)
M a n d i b l e s
( 1 p a i r )
M a x i l l a e
( 2 p a i r s )
Maxillipeds
(3 pairsl
Chelipeds
(1 pairl
Walking Legs
(4 pairsl
Abdomen Swimmerete
(5 paira)
Uropods
Telson
I
Completed
To exposeseveralimportant organsand blood vessels,remove a long, narrow section of the dorsal
abdominal exoskeletonas shown in the figure below.
ANTERIORDORSALAORTA
B e g i n c u t t i n g
a n d
f o l l o wd i r e c t i o n s
of arrows.
A B D O M I N A L
AORTA
D I C E S T I V E
G L A N D
C O N A D S
I N T E S T I N E
M U S C L E S
Completed
Attemptto locatethe heartandthe two blood vesselsleavingtheheart,the abdominalaortaandthe anterior
dorsalaorta.Sincethereareno veinsin crayfish,the blood flows from the dorsalblood vesselsto capillaries
andtheninto tissuespacescalledsinuseswhich functionasveins.
/ 0
HEART
OVARY
- Pericardial
cavity
Figure 29-
crayfish.
Intemal featuresof a
- Intestine
17.Cardiac stomach
1 8. G a s t r i cm i l l
29,'Esophagus
|
- Oviduct
2 1. 0 v a r y
- Sternalartery
- Venfial thoracic artery
26, Liver
- Gerebral
ganglia
- Pyloric stomach
It
Traceover
(drawin) andlabelthe testis/ovary andthe oviduct/spermduct in the diagrambelow. (Fromthe
paragraph above,you learnedtheseorgansandductsarein the samelocation(s)in themaleandfemale.
Onedrawingwith the duellabelswill takecareof the labeling.)
DigestiveandExcretorySystems
Carefullyremovesomeof the muscletissuein the anterior
part of the cephalothorax.Locatethe stomach,a
large,thin-walled,two-chamberedsacthat is
just above
the Mouth andesophagus.
Identiff the large,yellowish-green digestiveglandson eithersideof the stomachandpart of the intestine.
Ductsconnecttheseglands
to the
stomach.
Using a probe,separatethe digestiveglandsfrom the stomach to observewherethe stomach
joins the
intestine.Follow the intestinealongthe lengthof the abdomento the anus.The anusis locatedon the
ventralsurface of thetelson.
Locatethe pairedexcretoryorgans, or greenglands.Eachpair is anteriorto the stomachat the baseof the
antennabeneatheacheye. Find the excretorypore,or opening, at the baseofthe antennaeon the ventral
surface.
Labelthe stomach,mouth,esophagus, digestive
gland,intestine, anus,greengland,andexcretoryporeon
the diagrambelow.
r 3
NervousSystem
Placethe crayfishwith the ventralsideup. Usingscissors,carefullyremovethe soft tissuefrom the ventral
areaof the abdomen.
Completed
Locatethe slender,white ventralneryecordthat lies alongthe centralmidline of the crayfish.Note:Begin
tracingthe nervecordin the abdomen.Thethin platesof shellthat partly coverthe nervecordin the
cephalothoraxmakethe cord difficult to find in this area.Locateoneor moresegmentalgangliaon the
nervecord.
Find the brainjust above the esophagus.Carefullycut awaytherostrumandanyremaining
carapace.Betweenthe eyestalksis thebrain,a smallwhite mass.Note the nervestravelingfrom the brainto
the eyesandantennae.
Labelthe ventralnervecord,ganglia,andbrainon the diagrambelow.
Each of the crayfish's compound eyes is madeup of long visual rods. The outer surfaceof eachrod is called
a facet. Light is focusedthrough each facet onto the retina, producing aftuzy but wide-ranging image.
Remove an eye by clipping it at its baseand examine it with the
dissectingmicroscope.Note the numerousfacetsin the eye. Because
the eyes are on movable stalks, the crayfish has a very wide field of
view. How might this be an advantage?
Draw a view of what you seeunder the stereoscopein the field of view
circle to the right. Leave the eye in place on the stageso you instructor
can verity it.
Verified
The senseof touchis probablymoreimportantin the crayfishthan
vision.Touchreceptors arelocatedin specializedhairson thebody
as*'ell asin someappendages.
r
Magnification
GRA\rFISHg ilNTERNAt
STRUGTURE.
DIGESTruVESVSTENfi-
Nfi@UTH.
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INTESTINE'
DIGESTIVEGLAND.
ANUS'
EXGRET@RVSVSTENfi-
GREENGLAND,IP@RE,'
A
GIRGULATORVSVSTEM-
HEART,
PERIGARDilALSINUS;
ARTERV'
SINUS"
AFFERENTGANAL-
EFFERENTGANALO
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NON.CHITINOUS
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I I J D U t r
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PROTOPODITE
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\ L
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