Lab 2
Porifera, Cnidaria, and Platyhelminthes

    According to our classification scheme, the kingdom Animalia includes multicellular organisms having eukaryotic cells that lack cell walls, plastids, and photosynthetic pigments.  Most members of this kingdom take in nutrients by ingestion, with digestion taking place in an internal cavity.  Some take in nutrients by absorption and lack an internal digestive cavity.  All are heterotrophic, a term that means these organisms depend on substances produced by other organisms for their food source.

    The higher forms in the kingdom Animalia have evolved highly sophisticated levels of organization and tissue differentiation.  Reproduction for most of the organisms in this kingdom is sexual; and except for some of the lowest phyla, haploid cells occur only as gametes.

    In this exercise, you will study representatives of the phyla Porifera (sponges), Cnidaria (coelenterates), and Platyhelminthes (flatworms).  These animals are termed invertebrates because they lack the backbone found in vertebrates.  They are the lower invertebrate because they evolved first.

Question 1:  What kind of organisms does the Kingdom Animalia include?

Question 2:  Are you heterotrophic? Explain.

Question 3:  Why are sponges, coelenterates and flatworms called invertebrates?

 

LAB OBJECTIVES:
    1.  To be able to identify and classify all animals studies.

    2.  To be able to identify all slides studied and name distinguishing characteristics of each.

PROCEDURE:
    View the slide presentation depicting representatives of the three phyla.  Carefully read and work through the lab performing all of the described activities.

I.  Phylum Porifera - the sponges

The sponges are not considered as being on a direct evolutionary line toward "higher" animals.  Their structural complexity is not much above that of a simple colony of unicellular organisms.  The phylum name is a reference to the many pores or holes that penetrate their bodies.

Sponges are aquatic and predominantly marine.  The adults are always sessile and are usually found attached to submerged objects.  Sponge populations spread from one area to another due to their free-swimming flagellated larval form.

Sponges are multicellular organisms, but they display few of the features ordinarily associated with multi-cellularity.  Their low grade of organization is evidenced by the fact they have no organs of any kind; no digestive system, no circulatory system, and no nervous system.  Sponges do characteristically possess an internal skeleton composed of spicules.

The sponge's body is similar to a perforated sac and the inner wall is composed of flagellated cells called choanocytes or collar cells.  The beating of the internal flagella produces water currents; and the water, food particles, etc., are drawn in through the pore cells into the central body cavity (the spongiocoel).  The flagellated cells, and also wandering amoeboid cells, extract food particles and oxygen from the "incurrent siphon" (ostium); and carbon dioxide and nitrogenous wastes leave via the "excurrent siphon" (osculum).

Concerning the body shape of the Porifera, sponges are largely asymmetrical, although examples of radial symmetry may be found.

Question 4:  What is the meaning of the phylum name Porifera?

Question 5:  What are spicules?

Question 6:  Describe the body shape of sponges.

Question 7:  How does a sponge obtain food?

 

        A.  Obtain a slide showing a longitudinal section of the sponge, Grantia.  Observe the slide under 10X.  (Note: This is a long sponge, and you will have to scan up and down to see the whole section.)  Note the body wall of the sponge (basically two layers) and the central cavity of the sponge (the spongiocoel).  Refer to figures 1 and 2.

        B.  Obtain the slide which shows Grantia spicules.  View under 40X and turn the disc diaphragm slightly off center to reduce light.

Question 8:  Draw spicules.

        C.  Observe the preserved sponge specimens.

Question 9:  By what visible characteristic would you know that these animals belong to the phylum Porifera?


 

Figure 1:  Grantia General Construction

Figure 2:  Grantia Detail of  body wall

Figure 3: Obelia medusa form

II.  Phylum Cnidaria - the coelenterates

The members of phylum Cnidaria all possess stinging cells called cnidoblasts, hence the phylum name.  These animals are often called coelenterates (hollow guts) because of their body construction.

The phylum Cnidaria is composed of relatively simple animals whose radial symmetrical bodies display definite layers (an outer epidermis or ectoderm, an inner gastrodermis or endoderm, and a poorly developed middle layer, or mesoglea, composed of amoeboid or fibrous cells).  There are no distinct internal organs in this phylum (no head or central nervous system, but there is a nerve net).  The digestive cavity is a gastrovascular cavity, and it has only one opening, which serves as both mouth and anus.  There is no coelom between the outer body wall and the wall of the digestive cavity.  A circulatory system is absent, and segmentation is absent (unless associated with reproductive states).

The coelenterate body displays some division of labor and cell specialization.  There are epithelio-muscle cells, but no separate muscular system.  There are sensory nerve cells, but no central nervous system.  Gas transport is by simple diffusion, and nutrients are ingested and egested through food vacuoles.

Question 10:  What are cnidoblasts?

Question 11:  What type of body symmetry do Cnidarians have?

Question 12:  Describe the digestive cavity of Cnidarians.

 

Cnidarians will be studied with the aid of preserved specimens and representative slide of Hydra and Obelia.  You should thoroughly familiarize yourself with the coelenterate life cycle.

Cnidarians in their most complex life cycles can exist in two forms, the polyp form and the medusa form.  Some cnidarians demonstrate the complete life cycle.  Obelia is one of these.  Refer to figures 3 and 4.  Some exhibit only one phase of the life cycle.  Hydra is a coelenterate exhibiting only the polyp stage of the life cycle.  Refer to figure 5.


Figure 4: Obelia polyp colony showing reproductive and feeding polyps.


Figure 5: l.s. Hydra polyp with forming asexual bud.

     A.  Hydra
          1.  Obtain a slide which has Hydra mounted on it.  Refer to figure 5 and locate the basal disc, the column, the tentacles, the mouth, and the nematocysts.

13.  Question 13:  Draw and label the Hydra.

         

          2.  Make a wet mount of live Hydra.  Observe under both 4X and 10X.  Turn the disc diaphragm slightly off center to reduce the light.  Note the cnidoblasts that appear as swellings on the tentacles.  Tap the cover slip and note what happens to the cnidoblast.

     B.  Obelia
          Obelia is an organism which shows the alternation between two basic life forms - the polyp and the medusa forms.  The polyp form is actually a colony of polyps, and the polyps are of two types.  the first type is a nutritive polyp or feeding polyp.  Structurally it is much like the Hydra.  The second type is a reproductive polyp from the interior of which the medusa form is budded (asexual reproduction).  Obtain a slide of an Obelia colony and locate the structures labeled in figure 4.  When you have finished with the colonial forms, obtain a slide of the medusa form and locate the labeled structures underlined in figure 3.  The medusa demonstrates sexual reproduction in the organism.

Question 14:  Using drawings of the Obelia polyp colony and Obelia medusa from the slides you have observed, construct the life cycle of Obelia.  Use your lecture notes and text to fill in the missing parts. 

 

     C.  Observe and be able to recognize preserved specimens of Cnidarians.

 

Question 15:  Classify the preserved specimens into their respective classes.

 

III.  Phylum Platyhelminthes - the flatworms

All the animals in this phylum have bilateral body symmetry.  These animals are acoelomates (have no body cavity or coelom).  The phylum Platyhelminthes contains the flatworms.  Flatworms are flattened dorso-ventrally.  Their digestive cavity is described as incomplete indicating that there is one opening that serves as both mouth and anus (in the tapeworm there is no digestive tract).

Question 16:  What type of body symmetry do flatworms have?

Question 17:  What is an incomplete digestive system?

 

          A.  From the class Turbellaria you will observe the Planaria.  Obtain a permanent mount of a planarian worm and observe the following:
          1.  Eye spots on the anterior end
          2.  Mouth cavity in center of the body (which contains the withdrawn pharynx)
          3.  The digestive cavity

Question 18:  Draw a planarian from the prepared slide and label eye spots, mouth, digestive cavity and pharynx.  Refer to figure 6.

 

          B.  From the class Trematoda you will observe Clonorchis sinesis (human liver fluke).  Obtain a whole mount of Clonorchis, and identify the structures designated in figure 7.  The uterus of the fluke you are observing is filled with embryos or larva, each in a shell.  Note the large number.  Trace the excretory canal to see if it joins the digestive system.

          C.  From the class Cestoda, you will observe Taenia pisiformis (dog tapeworm).  All cestodes are parasites, and the adults live in the intestine of vertebrates.  In this lab you will observe their specializations for parasitism. 

Obtain a slide of Taenia pisiformis, and examine it both with a dissecting and compound microscope.  Observe and identify the designated terms in figures 8, 9, 10 and 11.  The immature proglottids may be found near the scolex (head with hooks), the mature proglottids near the middle, and the ripe or gravitid proglottids near the posterior end.

Question 19:  What is the function of the scolex?

Question 20:  What is the difference between mature and ripe proglottids?

 

          D.  Observe the preserved examples of Platyhelminthes.

 

Question 21:  What do all examples of this phylum have in common?

Question 22:  Classify the preserved specimens into their respective classes.

 


Figure 6:  Planarian digestive tract
 



Figure 7: Clonorchis sinesis, common liver fluke


Figure 8: Tapeworm Scolex and Neck


Figure 9: Immature Proglottid


 

                    Figures 10:  Mature proglottid

 

Figure 11: Gravid proglottid