Biology 120 Lab FLATWORMS, FLATWORMS, ROUNDWORMS AND SEGMENTED WORMS
Introduction Introduction to the Flatworms Flatworms Members of the phylum Platyhelminthes are commonly called called flatworms. There are both parasitic (dependent on a host organism for survival and freeli!in" forms of this group. !latworms" either parasitic or free#living forms" have both se$es on the same individual" a condition referred to as hermaphr#$itic. %nother term term that describes this condition condition is m#n#eci#%s. &ome parasitic species will self#fertili'e self#fertili'e their own eggs if another individual is not present. This group does not have a body cavity ( c#el#m and is referred to as ac#el#mate. !latworms are the first animal group to show all three tissue layers that we find in most animals (e$cept &ponges and nidarians. nidarians. This condition condition is referred to as tripl#&lastic. These three embryonic tissues are) ect#$erm" which forms the s*in or epidermis and nervous tissue" mes#$erm" which forms muscles and some organs" and en$#$erm" which forms the lining of the gastrovascular cavity or gut.
Introduction Introduction to the Roundworms Roundworms %ll roundworms" phylum Nemat#$a" are very similar in appearance) they have a cylindrical body with tapering ends. Most +ematodes are free#living" but some are important parasites parasites of plants and animals. %s for the flatworms" nematode development development includes all three embryonic tissue tissue layers. ,oundworms have a fluid#filled body cavity cavity"" that is lined on the outside by tissue derived from mesoderm. &uch a cavity cavity is called called a pse%$#c#el#m.
Introduction Introduction to the Segmented Segmented Worms Worms &ome worms are comprised of many segments. segments. These animals belong belong to the phylum phylum Anneli$a. Members of this phylum may be most familiar) the common earthworm" leech and nightcrawler belong to this group. group. There are three general types types of segmented worms. -ne group is entirely marine (the polychaetes" while the other two groups are either terrestrial or live in freshwater. %nnelids have a true coelom" a condition called c#el#mate. That is the the body cavity is lined on the inside and outside by mesoderm derived tissue.
Activities ou ou will be loo*ing at living specimens" preserved specimens for dissection" and preserved specimens for observation. observation. /lease handle all specimens with with care. !ollow the procedures procedures below and document your findings on the lab report.
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Freeli!in" Flat'#rms The free#living flatworm in the bowl at the front of the classroom is the common planarian Dugesia, which may be found under roc*s in cold" clean streams. -bserve the living planarian and note its general shape. hat type of body symmetry does it possess oes it have a head end % head end with a concentration of nervous tissue is called cephali(ati#n)
raw a s*etch of a planarian from either the living specimens or a whole mount microscope slide. %re the anterior and posterior ends the same or different here would you e$pect to find the animal3s sensory receptors and 4brain3 Label the head end on your s*etch. o you see any structures that may be sensory organs escribe them.
5$amine the planaria light demonstration and record your observations. o planaria prefer the light or the shade hat do you thin* are the benefits afforded to planaria
5$amine the /lanaria slide and draw6identify the following structures) Ocell%s, A%ricle, Anteri#r an$ p#steri#r &ranches #f intestine, E!erte$ pharyn* +pr#&#scis)
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7sing a prepared slide (planaria digestive tract w.m. or planaria plain and digestive tract w.m." s*etch the digestive tract of a planarian. 8s it simple li*e the cnidarians or more comple$ 9ow many openings to this tract do you see hat is similar and6or different about the gastrovascular cavity of the planarian compared with the hydra or :elly from last wee* hat might an advantage of the highly branched gastrovascular cavity be to flatworms
Parasitic Flat'#rms There are two types of parasitic flatworms) the tape'#rm and the fl%-e. Parasites are organisms that spend some portion of their lives in close association with their host organism. This relationship wea*ens and can even *ill the host. These organisms may live on the outside of the host (ectoparasites or within the host (endoparasites. Tapeworms seem to speciali'e in the gut tracts of many *inds of vertebrates" while flu*es are found in the blood stream or organs associated with the blood" li*e the liver. Loo* at the preserved specimens and slides of tapeworms and flu*es. +otice the body shape of each. hat do these animals use to anchor them in place on their hosts Both of these parasitic worms have comple$ life cycles; learn about flatworm parasitic life cycles.
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&*etch and label the tapeworm and flu*e from the prepared whole mount slides (the tapeworm slide is labeled Taenia pisiformis and the flu*e is Clonorchis sinensis. These are the species names for each animal. here do these organisms attach to their host Label these parts on the drawings.
&*etch and label the tapeworm (Taenia pisiformis scole$.
Nemat#$es The parasitic Ascaris lives in small intestine of humans and pigs" feeding on partially digested food. 8ts life cycle is shown in the preserved model. +ote that females can be distinguished from males because they are larger and do not have a curved or hoo*ed posterior end. raw and describe the Ascaris preserved specimen located on the counter with other specimens. an you identify males from females
&*etch a cross section of a nematode ( Ascaris lumbricoides m. = f. c.s.. !ind and label the muscles" uterus" intestine" pseudocoelom" dorsal and ventral nerve cords.
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raw and label the following nematodes) Enterobius vermicularis +pin '#rm, Nectar americanus, . Trichinella spiralis)
Anneli$a Be able to identify some representative members of %nnelida from the segmented worm# demonstrations.
atch an earthworm move. Based on its movement" predict what types of muscle annelid worms have.
raw a cr#ss secti#n of the earthworm (&lides) 5arthworm intestinal region c.s. = 5arthworm posterior to clitellum c.s.. 8dentify the muscles in the drawing. hat advantage might a segmented worm have over a non#segmented worm (e.g. Ascaris have in terms of movement
!inally identify (draw = label few internal structures.
Dissecti#n /nstr%cti#ns f#r Earth'#rm 1. issection should be done with care. /in each end of the preserved roundworm to the bottom of a wa$ed dissecting pan.. 2. ,efer to the illustration of worm dissection (diagrams are clearer than the photographs. 8dentify the dorsal (bac* side of your earthworm. 8t is dar*er than the ventral (belly side of the worm. /lace your earthworm dorsal side up in a dissecting pan. /in the earthworm to the dissecting pan by inserting a pin in the first and last segments. Try to place pins as close to the end of the worm as possible to avoid so that you do not pucturing any important structures. &tretch the worm slightly as you add the second pin.
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<. +e$t" identify the clitellum" a distinctive landmar*. The clitellum is a section of the worm that is about 1 cm long" where it appears lighter colored and has a slightly larger circumference than the rest of the worm. 8t is found closer to the anterior (front end of the worm. The end of the worm further from the clitellum is the posterior (rear end. Most of the interesting structures are found at the anterior end of the earthworm. /osterior to the clitellum" all of the segments are essentially identical. >. ou must now carefully cut the s*in of the earthworm and open it up to view internal structures without destroying them in the process. The best way to open the earthworm is with scissors. 8nsert the tip of the scissors about one inch posterior to the clitellum. Then lift up on the scissors to pull the s*in away from the delicate structures below as you cut. arefully cut forward from this point to the anterior end of the worm" *eeping the scissors held up where they will not damage structures below. ou may also cut posteriorly towards the pin holding the end of the worm in place. ?. /in open the incision as you cut so that the body cavity is e$posed. /lace the pins at such an angle that they will not obstruct your view. ou may need to gently use a dissecting probe to pry the s*in away from the structures below. @. Trace the digestive system from mouth to anus" paying special attention to the sections of the digestive tract that are modified to aid in digestion) pharyn$" crop" gi''ard" intestine. A. +ote the si'e (relative to other structures of the seminal vesicles and seminal receptacles ##sperm storage areas. . !inally" pull the intestine out of the way to reveal the ventral nerve cord.
Dra' the $issecte$ anneli$ an$ la&el s#me #f the ma0#r #r"ans y#% $isc#!ere$
