PRACTICAL 7 : Flatworms, Roundworms, and Rotifers Objectives At the end of this lab, students should be able to: i.
explain
the
basic
body
plan
of
some
members
of
phyla
Platyhelminthes, Platyhelminthes, Nematoda, and Rotifera. ii. ii.
iden identi tify fy str struc uctu turres and and fun funct ctio ions ns of of repr repres esen enta tati tive ve of of thes these e grou groups ps..
iii. iii.
stat state e char charac acte teri rist stic ics s of of mem membe bers rs of thes these e grou groups ps..
iv. iv.
expla xplain in the the dier dieren ence ce betw betwee een n acoel acoelom omat ate e and pseu pseudoc docoe oelo loma mate te,, and now which phyla associated with each.
Introduction !latworms of phylum Platyhelminthes, roundworm of phylum Nematode, and rotifers rotifers of phylum Rotifera live in marine, freshwater, freshwater, terrestrial, and parasitic environment. "heir morphology is more complex than that of sponges and #elly$sh. "hey have three germ layers: ectoderm, mesoderm, and endoderm %described as triploblastic& and have organ made of interdependent tissues and are the simplest animal having bilateral symmetry with with distinct anterior and posterior ends.
!latwo !latworm rms s have have soft, soft, wormli wormlie e bodies bodies and are are acoelomates acoelomates %lac of body cavity between the gut and body wall&. "hey represent an important evolution evolutionary ary transition transition because because they are the simplest forms to exhibit exhibit an organ system level of organi'ation and cephali'ation %a de$nite head with sense organ&. Although they are de$nite organs, the digestive system is still of the gastrovascular type, incomplete with a mouth and no anus. !latworms are grouped in three classes: class "urbellaria: Planarians, class "rematoda: !lue, and class (estoda: "apeworms.
Round oundwo worrms are are pseudocoelomates %hav %have e a fals false e body body cavi cavity ty or pseudocoel&. "hey have a complete gut with both a mouth and an anus. "ogether, "ogether, the pseudocoel and the complete digestive system comprise a tube)w tube)with ithin) in)a)t a)tube ube arran arrangem gement ent..
Roundwo oundworm rms s
have have
slende slender, r,
cylind cylindri rical cal
bodies that taper at both ends. A complex cuticle of protein covers them. !ree)living roundworms are Rhabditus and "urbatrix, Ascaris, and "richinella.
Rotifers are pseudocoelomates, microscopic animals, easily found in rain gutters and spouts, and in the slimy material around the bases of building. "heir body wall is very thin, usually transparent and covered by a cuticle composed of protein. "hey are dioecious* however, many species have no males, and the eggs develop parthenogenetically.
aterials Preserved or living specimens of :
(ompound
) Dugesia ( planaria&
microscope
) Taenia pisiformis
+issecting microscope lide and coverslip
Prepared
slide
of
Dugesia
( planaria ), Taenia pisiformis
(omplete
dissecting
set +istilled water
Procedure
!"#eriment $
:
Flatworms of #%&lum Plat&%elmint%es
Dugesia ( planaria ) (Figure 7.1) :
$'
A living Dugesia was obtained and its morphology was examined with a dissecting microscope. !eatures of planaria distinguish its head from its tail was identi$ed.
-.
A prepared slaide of a stained planaria was examined. "he ectoderm, mesoderm, endoderm, gastrovascular cavity, and muscular pharynx was identi$ed.
Taenia pisiformis (Figure 7.2) :
.
A preserved Taenia pisiformis was obtained. "he morphology of Taenia pisiformis, internal parasites of dogs and cat was loo for.
('
"he speciali'ed head or scolex, nec, and proglottis was identify at the body of Taenia pisiformis.
)'
/sing a prepared slide, hoos and sucers was identi$ed. "as that the tape worm used these hoos and sucers was identi$ed.
Fi*ure 7'$ : Anatomy of a planarian. %A& +orsal view of digestive and nervous system. %0& (ross section and %(& longitudinal section of
planarian taen through the pharynx region. %+& 1ateral view. %2& +orsal view. %!& agittal view of reproductive system.
Fi*ure 7'( : tructure and life cycle of the beef tapeworm, Taenia saginatus.
+iscussion :
3n the ingdom Animalia,the phylum Platyhelminthes represents all 4atworms."here are bilaterally symmetrical, having an anterior, posterior, dorsal, and ventral end and two seemingly identical lateral surfaces. 5owever, 4atworms is lacs of any type of body cavity, a 4uid $lled space between the digestive tract and the body wall. "he area of 4atworm is $lled with tissue. !latworms have primitive brains, comprised of clusters of nervous tissue. "wo long nerve cords run the length of the body, and they branch to form small nerves running throughout the body. Another hallmar of 4atworms is a lac of a complete digestive tract. !latworms tae in food and excrete waste from one single hole. "he opening in the gastrula never fully evolves in 4atworms to mae a tract that travels from one hole in the anterior end to another hole in the posterior end, which would mae the tract complete. "here are four classes that mae up the phylum Platyhelminthes, each with uni6ue structures and living styles which is "urbellaria, (estoda, 7onogenea. 3n the experiment, "aenia pisiformis come from class (estoda also nown as tapeworms while +ugesia sp Planaria common name planaria come from class "urbellaria.
!"#eriment (
:
Roundworm of #%&lum ematode
Ascaris (Figure 7.3) : . A female and male Ascaris was examined and identi$ed the mouth and anus. -. 0y using a prepared slide of female Ascaris, ectoderm, muscle $bers, intestine, oviducts, loops of ovaries, uteri, and pseodocoel was identi$ed. 8. 0y using a prepared slide of male Ascaris, ectoderm, muscle $bers, intestine, loops of testis, seminal vesicle, and pseodocoel was identi$ed.
Fi*ure 7') %A& 1ateral view of female nematodes. %0& 1ateral view of male nematodes. %(& and %+& (ross section of the body.
+iscussion "he -9,999 nown nematode species inhabit terrestrial, marine, and freshwater environments and are found in almost all moist habitats. "he taxon includes numerous plant and animal parasites, many of which are of medical or agricultural importance, but most are free)living %non) parasitic&. 7ost nematodes, or roundworms, are long, slender, almost featureless externally, tapered at both ends, and round in cross section. "he body cavity, if present, is a hemocoel derived from the blastocoel. "he body is covered with a thic extracellular cuticle secreted by a cellular or syncytial epidermis that is molted during #uvenile development. "he epidermal nuclei are sunen below the epithelial layer into four longitudinal epidermal cords that extend the length of the animal. "he body wall has well)developed longitudinal but no circular muscles. "he gut is complete with terminal anterior mouth and subterminal posterior anus. 3t comprises ectodermal foregut and hindgut and an endodermal midgut. "he body cavity, or hemocoel, is not lined with mesothelium and there is no muscle, connective tissue, or other mesodermal derivative associated with the midgut. "he nervous system is a ganglionated circumenteric ring, hence the name cycloneuralia;, with several longitudinal nerve cords, the most important of which is the ganglionated, double, ventral cord. "he nerve cords are located in the longitudinal epidermal cords, along with the epidermal nuclei. (ytoplasmic innervation processes from the longitudinal muscles extend to the longitudinal nerve cords and serve the function of motor neurons, which are absent. ensory e6uipment may include uni6ue chemosensory amphids and sensory bristles around the mouth.
7ost nematodes lac cilia or 4agella, even in the sperm. "here are, however, ciliary derivatives in the amphids and cilia are present in the gut epithelium of some nematodes. Roundworms are ammonotelic and nitrogen excretion is mostly by diusion across the body wall. 8 mm& and free)living but some of the parasitic species, such as Ascaris, may reach ?9 cm. Ascaris is an intestinal parasite in pigs. Parasitic nematodes tend to be much larger than free)living nematodes. +igestive tract, when it is compare this slide to the whole preserved Ascaris. 3f you dissect one of those specimens, it will show that the internal organs %gut and reproductive organs& are simply hanging free inside the body cavity, or pseudocoel. 3n this cross) section, the intestine doesn@t appear to be attached at all, and if you loo closely %at 9x magni$cation&, will show that the wall of the intestine consists of #ust one layer of epithelium, with no other tissue layers attached. Reproductive organs are ovary is maes the eggs and uterus is stores eggs until they are released for external fertali'ation. "he male diers mainly in terms of its reproductive organs is where testis is a long tube, looping bac and forth throughout the body* in this cross)sectional view, there appear to be multiple separate testes. "he testis maes sperm. "he vas deferens %also called ductus deferens& is
another part of the same tubular male reproductive tract* it is responsible for storing and maturing sperm.
Post-lab Questions
.
5ow
is
bilateral
symmetry
dierent
from
radial
symmetryB
Radial s&mmetr& ea anemones display radial symmetry."hese organisms resemble a pie where several cutting planes produce roughly identical pieces. An organism with radial symmetry exhibits no left or right sides. "hey have a top and a bottom %dorsal and ventral surface& only. 7ost radially symmetric animals are symmetrical about an axis extending from the center of the oral surface, which contains the mouth, to the center of the opposite, or aboral, end. "his type of symmetry is especially suitable for sessile animals such as the sea anemone, 4oating animals such as #elly$sh, and slow moving organisms such as star$sh.
-ilateral s&metr& 3n bilateral symmetry %also called plane symmetry&, only one plane, called the sagittal plane, will divide an organism into roughly mirror image halves. "hus there is approximate re4ection symmetry.
e.g. in the case of an animal with a main direction of motion in the plane of symmetry.
-.
Chat are the advantages of a roundwormDs digestive system having two openingB "he roundworm can continue eating, and the ingested material will be processed appropriately, with dierent chemicals dumped into it at dierent locations along the length of the alimentary canal to assist in the digestion of the material. 3t provides for se6uential processing of the material in a spatial manner. "he planaria, by contrast, has to use a time)based manner for processing of ingested material."hat is, for best eEciency, it would eat its $ll $rst, and then have time)based events in the digestion rather than location)based.
8. +escribe several adaptations of parasitic 4atworms to their external environment. A parasitic 4atworm has less)evolved digestive system, since they absorb the nutriens directly from the host, having no point to digest further. "hey also have more complex reproductive life cycle, where they lay eggs that will be put in the feces. "hen a food will be contaminated with eggs, new 4atworms will develop to other hosts. Also, parasitic 4atworms will usually have hoos on the scolex %anterior region& to attach it to the wall of the gut, and they have an extra outer covering %glycocalyx& to protect it from being digested.
