Kingdom Animalia: Phyla Porifera and Cnidaria

Transcription

1 Kingdom Animalia: Phyla Porifera and Cnidaria Essential Question(s): What are key characteristics to the animal kingdom? Objectives: 1. Students will be able to distinguish essential characteristics in the animal kingdom. 2. Students will be able to differentiate between phyla of the animal kingdom 3. Student will recognize defining attributes in the Porifera and Cnidaria phylas. In the following chart are the listed traits of animals and associated new vocabulary. Examine the chart below and new vocabulary. Kingdom Animalia Cell Feature Body Plan Nutrition Life Cycle Eukaryotic, no chloroplast present, small cells Multicellular, Highly differentiated, Motile, Blastula, Gastrulation Heterotrophic, may be predators or parasites. Haploid (sperm and egg) and diploid(multicellular) phase Introduction: Animals originated in the oceans of the Precambrian era about 1.5 billion years ago. The first animals were multicellular, eukaryotic and heterotrophic. They were the first predators. By the beginning of the Cambrian period (543 mya), sponges and cnidarians were already present. During the end of the Precambrian and the beginning of the Cambrian, a huge diversification of the animals took place. This is called the Cambrian Explosion, although it spanned the Cambrian-Precambrian boundary (565 to 525 mya). Most extant phyla are directly traced to this period. During this period, animal phyla displayed dramatic variation in tissue formation, body symmetry, gut tube formation, major feeding structures, molting strategies and skeletal arrangements. These evolutionary trends, through natural selection, resulted in the major animal lineages of today. In this particular lab we will study the first two phyla, Porifera and Cnidaria. 1

2 Three essential characteristics to observe while progressing through each animal phyla are symmetry, cephalization, and body cavity. There are two types of symmetry present in animals, bilateral like humans, and radially symmetrical like a wheel. As the exception, sponges do not exhibit any type of symmetry. Cephalization, having a head, only occurs in bilaterally symmetrical animals where the brain and most of its sensory organs are located. Throughout this lab you will observe acephalic organisms and one cephalic organism. Body cavity refers to having an area where digestive and other internal organs form and reside. Though Poriferans and Cnidarians do Figure 1: Sea-anemone (cnidarian) illustration showing radial symmetry not have body cavities they will be included in the next animal specimens to be observed. Phylum Porifera The basic body form of all sponges is a sac-like structure consisting of three sections, outer-most epidermal cells and aggregations of specialized cells beneath them, such as flagellated cells called choanocytes; and clusters of amoeboid cells that form skeletal structures of various sorts. These cell groupings are perforated by a large number of small pores and canals. The main cavity of this sac-like arrangement is called the spongocoel and has at least one large opening to the outside, called an osculum. The sponges are taxonomically classified based on the type of skeletal elements produced. Figure 2: Sea Sponge labeled diagram. 2

3 These include calcareous spicules, siliceous spicules, or proteinaceous spongin fibers. This leads to the basic sponge taxonomy, which includes three classes. Sponges in the Class Calcarea have calcium carbonate spicules, which have three or four rays. All of these sponges are marine. The Class Hexactinellida have siliceous spicules, which are 6 rayed. These sponges are all marine and most often cylindrical in form and found in deep water. The Class Demospongiae are typically called bath sponges because they are used by humans for bathing. These sponges have spongin fibers, or siliceous spicules, or both. They represent over 90% of the sponges in the world, and one family is found in fresh water. In all sponge types, the body is designed to facilitate filter-feeding. Water is pulled into the pores and canals by the beating of the flagella of choanocytes. The water moves into the spongocoel and is eventually forced out through the osculum. As the water passes across the choanocytes, food particles (microscopic algae, bacteria, and organic debris) adhere to the cells and are eventually taken into food vacuoles for intracellular digestion. Figure 3: 1=Porifera body structure. Colour-coding: *Yellow: pinacocytes *Red: choanocytes *Grey: mesohyl * Pale blue: water flow Structure types: *Left: asconoid *Middle: syconoid *Right: leuconoid Re 3

4 Figure 4: Scanning electron micrograph images of a selection of microscleres and megascleres of demosponges, not to scale, sizes vary between 0.01 and 1 mm. Observe: 1) Obtain a preserved specimen of Grantia, look closely and try to see how their bodies are designed to move water in order to feed and move water. a. Are any of the features observed in Grantia those of an animal? Explain. 2) Examine a slide of a Grantia cross-section. Pay close attention to the folded body wall. a. Draw your observation indicating the external environment and the Spongocoel. b. Label choanocytes and amoebocytes from your previous drawing. Figure 5: Grantia cross section Figure 6: Spongin fibers (left) Figure 7: Isolated Spicules (right) 4

5 3. Examine a prepared slide of sponge fibers. These are the commercial sponges. Cnidaria: Members of the largely marine Phylum Cnidaria are considered to be more "advanced" than the poriferans for two major reasons. First, they are the first animal to show multicellular layers, i.e. tissue level organization, although they have no organs. Second, the adult forms are derived from two distinct embryonic germ layers, the ectoderm and the endoderm hence, they are diploblastic. Higher phyla are triploblastic (derived from three distinct embryonic germ layers). The organisms in the phylum Cnidaria are characterized by radial symmetry. Terms for direction use the mouth as a point of reference. The end of the organism which contains the mouth is oral; the opposite end of the animal is aboral. Radial symmetry refers to the fact that any plane passing through the oral-aboral axis divides the animal into two equal halves, or that the body tends to radiate out from the oralaboral axis like spokes of a wheel. The basic body plan of the cnidarians is a sac-like structure, with a gastrovascular cavity. The gastrovascular cavity has a single opening which serves as both mouth and anus; it is often surrounded by tentacles. The body wall has an external cell layer, the epidermis; an internal cell layer, the gastrodermis that lines the gastrovascular cavity; and a jelly-like layer between these two, called the mesoglea which may be either cellular, or more often, acellular. Unique cellular components, called nematocysts are found in cells called cnidocytes. Cnidocytes (hence the phylum name Cnidaria) are especially abundant on tentacles, but may be generally distributed throughout the epidermis and gastrodermis. 5

6 Figure 8. Diagram of a cross section of a jellyfish (Olindias formosa) showing the main parts of a jellyfish The life cycle of a typical cnidarian alternates between an often sessile polyp stage and a freeswimming medusa stage. The existence of two distinct forms such as this is known as developmental polymorphism. Both stages exhibit the radial body plan described above; however, the polyp stage is cylindrical and attached at the aboral end to a substrate, while the medusa stage is flattened or domed in appearance with the mouth oriented downward. In Scyphozoans the polyp is an asexual stage, while the medusa is a sexual stage. In some Cnidarian classes, either the polyp or the medusa stage may be reduced or completely absent (e.g. Hydra). You will examine the three classes of the Phylum Cnidaria: Class Hydrozoa, Class Scyphozoa, and Class Anthozoa. 6

7 Summary characteristics of class Hydrozoa and specific specimens. Class Hydrozoa Specimen 1 : Hydra Specime 2: Obelia Specimen 3: Physalia Specimen 4: Ganoneimus *Dominant Polyp stage *Germ layers are separated by acellular mesoglea *Ectodermal cells have cnidocytes and muscular contractile cells *Endodermal cells secrete enzymes for digestion *Small * lives in shallow freshwater *Prey on smaller invertebrates *Do not have medusa stage *Has colonial polyps *Polymorphic polyps *Gastroid polyps are for feeding *Gonozoid polyps are for reproduction. *Floating polymorphic colony of polyps *Gas filled polyps for floatation *Nutritive polyps make up long tentacles *Tentacles are lethal for small fish *Large medusae *Gonads attach to radial canals and appear similar in males and females *Tentacles have a rough surface Figure 9: Hydra budding 4X Observe: 1) Obtain a live Hydra sample. Allow a few minutes for specimen to relax in petri dish and then observe under a dissecting microscope. 2) Tap the edge of petri dish and observe behavior of Hydra. Place live Daphnia near Hydra tentacles. a. Describe your observations. b. What tissues must exist for the behaviors observed? 3) Examine prepared slides of budding hydras and a cross section of hydra showing endoderm and ectoderm. 7

8 Figure 10: Obelia 4X Figure11: Obelia Medusae 40X Figure 12: Physalia Tentacle 3) Under a microscope examine prepared slide of both polyp and medusae of Obelia. Differentiate a feeding polyp from a reproductive polyp. 4) Examine preserved sample of Gonionemus, Class Scyphozoa Commonly called the jellies are the Aurelia and Cassiopeia. The planula is the typical larva of a cnidarian. After sexual reproduction, this larva is formed; it swims to a new location and develops into a polyp or medusa. The gelatinous medusa is the dominant body form in the life cycle of Schyphozoans. Class Anthozoa: Corals Figure 13: Jelly cc10 Corals are colonial cnidarians, often having huge numbers of polyps. They have internal skeletons, which you see here. You should be able to see the small holes where the polyps lived. When the coral was alive, the entire skeleton was covered by a skin of living tissue. These corals made their living mostly by symbiosis with photosynthetic zooxanthellae, a type of dinoflagellate (Protista) 8

9 Observe: 1) Examine anthozoans on display. a. How does the feeding method of a sponge compare with that of a coral? Introduction to the Flatworms: Phylum Platyhelminthes Flatworms. The acoelomates are animals that lack a coelom. Acoelomates lack a body cavity, and instead the space between the body wall and the digestive tract is filled with muscle fibers and loose tissue called parenchyma. These animals possess three living cell layers (i.e.: ectoderm, mesoderm, and endoderm) which makes them triploblastic. The Platyhelminthes, or flatworms are an economically important group because they Figure 14: Coral Polyp anatomy include the parasitic tapeworms and flukes, which affect both humans and the livestock we depend on. These acoelomates are advanced over other radiate animals in several ways. 1. Their bilateral symmetry adapts them for direct movement. 2. Their tissues are well defined and organized into complex organs. 3. The nervous system is organized and concentrated in the anterior end of the animal (cephalization). 4. They do not depend on simple diffusion for elimination of nitrogenous wastes, but have an excretory system based on structures called flame cells.5. They possess a complex digestive tract with both a mouth and anus. Figure 15: Planaria Body plan 9

10 Class Turbellaria (Planarians) Planarians are found on the underside of stones and submerged leaves or sticks in freshwater springs and ponds. They are often confused with leeches, which they resemble in size, shape and color. Unlike leeches planarians are not segmented and usually do not resort to blood meals. Slides of stained Turbellaria (Planaria) View slides of stained whole mount of planaria. Sketch and label the digestive Figure 16: Planaria digestive tract 4X system in your preparation. Observation of live Planarians Gently, using forceps, an eyedropper or a finger, place a live planarian in a petri dish with the spring water provided. Periodically replace the water as it evaporates. External Structures: Observe the animal and decide which is the anterior, posterior, dorsal and ventral surface. On your live specimen note the ear-like auricles. These structures bear sensory cells but they are tactile neither auditory nor olfactory. Note the eyes, do they possess lenses? Locomotion: Note how your specimen moves across the petri dish. This gliding movement is accomplished in part by mucus on which the planarian moves via cilia. The body is also propelled by waves of muscle contractions. Note how the animal will shorten and lengthen its body length to accomplish movement. 10

11 Reactions to Stimuli: Observe the responses of planarians to touch (thigmotaxis) and light (phototaxis) through the following experiments: - Response to touch. Very gently touch the outer edges of the worm with a probe or pencil. Which parts of the body are the most sensitive? - Response to directional illumination. Direct a strong light at the planarians from one side of the dish and observe their movements. Periodically, move the dish around the light pausing to note the animal's response. Is the response random or directional? Class Trematoda (Flukes) All trematodes are parasitic, harbored in or on a great variety of animals. Many have two intermediate hosts before reaching the final host. Examine a slide of Schisistosom jamonicum. An odd feature of this genus is the strong sexual dimorphism. The males are stouter than the females and have a longitudinal groove called the gynecophoric canal. Even odder, the thinner female normally resides there, permanently embraced by the male. Note the strong oral sucker and secondary sucker near the anterior end. Figure 17. A fluke showing internal anatomy. Class Cestoda (Tapeworms) Tapeworms are all endoparasitic and show extreme adaptations to their existence through the complete loss of their digestive tract, and a focus Figure 18. An adult tapeworm. 11

12 on reproduction. Most require a single intermediate host and a final host, where the adult tapeworm resides. As their name implies their long bodies are usually made of segments called proglottids. As new proglottids are formed anteriorly the older ones are pushed towards the tail, hence the most mature proglottids are found at the posterior end. The scolex is located on the head and is used for attachment. Examine the preserved slides of Taenia pisiformis. Attempt several sketches of the scolex and suckers, which are used for attachment. Sketch both mature and immature proglottids if present. Label the structures you can discern. Since tapeworms are hermaphroditic each proglottid contains both male and female gonads. The mature proglottid contains a genital pore laterally (on the side). From this pore two tubes extend into the interior. The anterior, convoluted tube, which branches in the middle of the proglottid, is the sperm duct. It branches to the different testes in the segments. The posterior duct is the vagina, which connects to the ovaries via the oviducts. Planarian Regeneration Experiment: As we learned in class planarians have incredible powers of regeneration. It's now time to make some cuts! Now pair up with another classmate. 1. Clean razor blade or sharp scalpel 2. A clean petri dish with cover and partially filled with spring water 3. Obtain two flatworms per group Procedure: Using a pair of forceps, place the planarian on a piece of tissue paper and place both on a cube of ice. The planarian will immediately extend and become catatonic. 12

13 Place the ice, tissue paper, and planarian under a dissecting microscope and decide how you want to cut your worms. If you decide to make longitudinal cuts make sure the cut is clean and has completely separated the cut surfaces. Place the cuts and cut planarians into the petri dish (with your name on the cover) and place in a cool place. To insure the health of our specimens the water must be changed every 3 days with fresh spring water. At each water change remove any dead pieces which will appear fuzzy and gray. Use the attached tables on the following page to sketch your initial cuts. At each water change (every 3 days) examine and sketch the regeneration of new body parts. Observe the specimens for 1 week. Important: If you make longitudinal cuts for 2 headed worms, you will need to renew the cuts 1 and 2 days after the initial incisions. This is done to prevent the two pieces fusing back together. 13

14 Sources: 1. De Anza Lab Manualhttp://faculty.deanza.edu/heyerbruce/bio6a 2. Survey of the Animal Kingdom : Phyla Porifera, and Cnidaria 3. Image Sources: Figure 1 - Sea anemone Figure 2: Sea Sponge labeled diagram. m.svg Figure 3: Figure 4: Scanning electron micrograph images of a selection of microscleres and megascleres of demosponges, not to scale, sizes vary between 0.01 and 1 mm. Figure 8: Diagram of a cross section of a jellyfish (Olindias formosa) showing the main parts of a jellyfish Figure 13: : "Jelly cc10". Licensed under CC BY-SA 2.0 via Wikimedia Commons - Figure 14: Figure 17: Fugure 18: 14