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BIO170 General Biology Freeman/Mac Leod FMCC PORIFERA AND CNIDARIA Objective: After completing this exercise, you should be able to do the following: Compare the anatomy of the representative animals describing similarities and differences in organs and body form that allow the animal to carry out body functions. Discuss the relationship between body form and the lifestyle or niche of the organism. Describe features of the phyla: Porifera and Cnidaria. Introduction Animals are classified in the domain Eukarya within the unikonta (1 flagellum) lineage. They are the only multicellular organisms that are heterotrophic via ingestion. Careful study of comparative anatomy, embryology, and most recently genetic and molecular data, reveals many similarities in structure and development. Collectively, this evidence implies an ancestral evolutionary relationship among all animals. Scientists recognize over 30 phyla of present-day animals based on differences in body architecture. A. STUDYING ANIMAL FORM AND FUNCTION In this and the following lab exercises, you will investigate body form and function in examples of several major groups of animals. You will use these investigations to ask and answer questions comparing general features of morphology and relating these features to the lifestyle of each animal observed. The animals you will study in the next few lab exercises are sponge, hydra, planarian, earthworm, clam, crayfish, grasshopper, sea star and pig. As you study each animal, relate your observations to the unifying themes of this course: phylogenetic relationships, criteria that are the basis for animal classification, the relationship between form and function, and the relationship of the environment and lifestyle to form and function. Some of this will become more apparent as we work through chapters 41-48 in your lecture textbook. In your comparative study of these organisms, you will investigate 13 characteristics. Before you begin the dissections, become familiar with the following characteristics and their descriptions: 1. Symmetry. Is the animal radially symmetrical (part arranged around a central axis), bilaterally symmetrical (right and left halves are mirror images), or asymmetrical (no apparent symmetry)? 2. Tissue organization. Are cells organized into well-defined tissue layers (structural and functional units)? How many distinctive layers are present? Remember that embryologically these tissue layers are ectoderm, mesoderm and endoderm. 3. Body cavity. Is a body cavity present? A body cavity – the space between the gut and the body wall – is present only in three-layered organisms, that is, in organisms with the embryonic germ layers ectoderm, mesoderm and endoderm. There are three types of body forms related to the presence of the body cavity and its type (figure 2): 1 BIO170 General Biology Freeman/Mac Leod FMCC a. Acoelomate - without a body cavity. Tissue from the mesoderm fills the space where a cavity might be; therefore, the tissue layers are closely packed together. b. Pseudocoelomate - a cavity between the endoderm and the mesoderm. c. Coelomate - cavity within the mesoderm (completely surrounded by mesoderm). Figure 1: The three types of body plans 4. Openings into the digestive tract. Can you detect where food enters the body and digestive waste exits the body? Some animals have only one opening, which serves as both a mouth and an anus. Others have a body organized as a “tube within a tube,” with an anterior mouth and a posterior anus. 5. Circulatory system. Does this animal have open circulation (the blood flows through coelomic spaces in the tissue as well as in blood vessels), or does it have closed circulation (the blood flows entirely through vessels)? 6. Habitat. Is the animal terrestrial (lives on land) or aquatic (lives in water)? Aquatic animals may live in marine (sea) or fresh water. Note how the organism is adapted to its habitat. 2 BIO170 General Biology Freeman/Mac Leod FMCC 7. Organs for respiration (gas exchange). Can you detect the surface where oxygen enters the body and carbon dioxide leaves the body? Many animals use their skin for respiration. Others have special organs, including gills in aquatic organisms and lungs in terrestrial organisms. 8. Organs for excretion. How does the animal rid its body of nitrogenous waste? In many animals, these wastes pass out of the body through the skin by diffusion. In others, there are specialized structures. You will learn about these structures as we investigate each organism. 9. Type of locomotion. Does the organism swim, crawl on its belly, walk on legs, burrow in the substrate, or fly? Does it use cellular structures, such as cilia, to glide its body over substrate? 10. Support system. Is there a skeleton present? Is it an endoskeleton (inside the epidermis or skin of the animal) or is it an exoskeleton (outside the body wall)? Animals with no true skeleton can be supported by water: fluid within and between cells and in body chambers such as a gastrovascular cavity. A coelom may provide a hydrostatic skeleton. 11. Segmentation. Can you observe linear repetition of similar body parts? The repetition of similar units, or segments, is called segmentation. Can you observe any degree of segmentation? Have various segments become modified for different functions? 12. Appendages. Are there appendages (organs or parts attached to a trunk or outer body wall)? Are these appendages all along the length of the body, or are they restricted to one area? Are they all similar, or are they modified for different functions? 13. Type of nervous system. Do you see a brain and nerve cord? Is there more than one nerve cord? What is the location of the nerve cord(s) (dorsal or ventral)? Are sensory organs or structures present? Where and how many? Do you see signs of cephalization (the concentration of sensory equipment at the anterior end)? What purpose do such structures serve (for example eyes for light detection)? As you carefully study or dissect each organism, refer to these 13 characteristics, observe the animal and record your observations in the summary table provided to you. Tape or paste that table into your notebook. 3 BIO170 General Biology Freeman/Mac Leod FMCC B. PHYLUM PORIFERA – THE SPONGES Introduction Within the animal kingdom, sponges are separated from all other animals because of their unique body form. This phylum consists of approximately 7000 species all of which are benthic; they live attached to the bottom of aquatic environments. Sponges are characterized by the possession of a feeding system unique among animals. Poriferans don't have mouths; instead, they have tiny pores (ostia) in their outer walls through which water is drawn (figure 2). Water enters through the ostia, flows through canals to a spacious chamber called a spongocoel, and finally exits through large openings called oscula. Sponge cells perform a variety of bodily functions and appear to be more independent of each other than are the cells of other animals. Sponges come in an incredible variety of colors and an amazing array of shapes. They are mostly marine living animals found at all latitudes beneath the world's oceans. Generally, they are sessile, though it has been shown that some are able to move slowly (up to 4 mm per day) within aquaria. Some sponges reproduce asexually but the primary method of reproduction is sexual (Figure 3.) Sperm, released by the male, travel to the female where they are taken up by choanocytes. The choanocytes deliver the sperm to amoebocytes that move through the mesohyl. The amoebocytes deliver the sperm to the egg for fertilization. The zygote develops in to a motile larva that is released to find a place to settle and develop into a new sponge. You will observe the unique sponge structure by observing first a preserved specimen and then a prepared slide of a section taken through the longitudinal axis of the marine sponge Scypha. You will be able to observe other more complex and diverse sponges on demonstration. Procedure: 1. Refer to your photo atlas pg. 83-85 as you work through this exercise. 2. Obtain the preserved sponge Spongilla. Using a stereoscopic microscope observe its external characteristics. a. Note the vase-like shape of the sponge and the osculum, a large opening in the body at one end. The end opposite the osculum is the holdfast that attaches the animal to the substrate. b. Note the invaginations in the body wall, which form numerous fold and channels. Identify the ostia. You may be able to observe needle-like spicules around the osculum and protruding from the surface of the body. These spicules are made from calcium carbonate or silica. They give support and provide protection by preventing small animals from entering the sponge’s internal cavity. c. Draw and label the bold terms above in your notebook. 3. Obtain a prepared slide of Scypha, longitudinal and cross section. Use a compound microscope. a. Follow the path that water would take through the organism. i. Find an ostium, incurrent canal, radial canal and the spongocoel. 4 BIO170 General Biology Freeman/Mac Leod FMCC ii. Draw these in your notebook and indicate current flow by drawing an arrow from outside the organism into the spongocoel. b. Note the structure of the body wall. You should be able to observe 3 kinds of cells. i. One cell type that is unique to sponges is the choanocyte (or collar cell). These cells line the spongocoel and the channels leading to it. Each collar cell has a flagellum extending from its surface. The collective beating of all flagella moves water through the sponge body. Small food particles taken up and digested by collar cells are one major source of nutrition for the sponges. How would you hypothesize about the movement of oxygen and waste throughout the sponge body and into and out of cells? ii. Epidermal cells form a continuous protective layer over the outside of the organism. iii. The third type of cells is called amoebocytes. These cells digest and distribute nutrients from the choanocytes to the epidermal cells. They also transport waste and help with repair and reproduction. As their name suggests, they move like amoebas through the mesohyl (a gelatinous matrix of protein that also houses the spicules and a substance called spongin) of the sponge. iv. Draw and label the bold terms above in your notebook. 4. Observe examples of more complex sponges on demonstration. The body of these sponges, sometimes called “bath sponges”, contains a complex series of large and small canals and chambers. The same cells that were describes in Scypha are present in bath sponges, but, in addition to spicules, there is supportive material that consists of a soft proteinaceous substance called spongin. These sponges often grow to fit the shape of the space where they live, and observing them gives you a good clue about the symmetry of the sponge body. a. How would you describe the symmetry of sponges? 5. Complete the summary table provided, filling in all information for sponge characteristics in the appropriate row. Tape or paste this table into your notebook. You will be adding data over the next few lab exercises. 5 BIO170 General Biology Freeman/Mac Leod FMCC Figure 2: Anatomy of a sponge Figure 3. Reproduction and Development in Poriferans C. PHYLUM CNIDARIA - JELLYFISH, CORALS, SEA ANEMONES Introduction The name Cnidaria comes from the Greek word "cnidos," which means stinging nettle. Casually touching many cnidarians will make it clear how they got their name when their cnidocytes (stinging cells) eject barbed threads (nematocysts) tipped with poison (Figure 4.). Cnidarians are united based on the presumption that their cnidocytes have been inherited from a single common ancestor. This adaptation allowed them to become successful marine predators. Today there are about 11,000 species in four lineages: the Hydrozoa (hydroids), Cubozoa (box jellyfish), Scyphozoa (jellyfish), and Anthozoa (anemones, corals and sea pens). 6 BIO170 General Biology Freeman/Mac Leod FMCC Typical cnidarians are radially symmetric diploblasts (Figure 5). The outer epidermis contains the cnidocytes. The gastrodermis lines the gastrovascular cavity, which in some cnidarians may be divided up by septa or elaborated into branching canals. In between epidermis and gastrodermis is the mesoglea, a layer of jellylike substance which contains scattered cells and collagen fibers. A ring of tentacles often, but not always, surrounds the mouth (which also functions as an anus). Cnidaria reproduce sexually (Figure 6). During their life cycle, they take on both a medusa forma and a polyp form. The medusa produces gametes that are shed in the water. The fertilized egg develops into a mobile planula larva which settles and develops into a polyp. Medusae are produced asexually from the polyp and are released to be dispersed. Figure 4. Cnidocyte with nematocyst Figure 5. Anatomy of Cnidaria 7 BIO170 General Biology Freeman/Mac Leod FMCC Figure 6. Cnidaria Life Cycle Figure 7. Hydra nerve net Procedure: 1. Refer to your photo atlas pg. 86-87 as you work through this exercise. 2. Place several drops of culture water in a depression slide. Use a pipette to obtain a living hydra from the culture and place it in the drops of water. Using a stereoscopic microscope observe the hydra structure a. Note any movement, the symmetry and body structures present (see bold terms above) b. Draw and label the bold terms above in your notebook. 3. Add one or two water fleas (Daphnia) to the slide and note the hydra’s behavior. a. Set the slide aside and return to it in a moment. 4. Obtain a prepared slide of Hydra. a. Draw and label the bold terms above in your notebook. 5. Not visible with the microscope is a network of nerve cells in the body wall, which serves as the nervous system; there is no concentration of nerve cells into any kind of brain or nerve cord (Figure 7). 6. Observe the central cavity, called a gastrovascular cavity. Digestion begins in this waterfilled cavity (extracellular digestion), but many food particles are drawn into cells in the gastrodermis lining the cavity where intracellular digestion occurs. 7. To better observe cnidocytes and nematocysts, turn your attention again to your living hydra and follow this procedure: a. Use your living Hydra preparation from the previous procedure carefully place a coverslip onto this depression slide. Place the slide on the stage of a compound microscope and observe your living hydra first using the scanning and then the low 8 BIO170 General Biology Freeman/Mac Leod FMCC power objective. Make sure your light source is not heating up the slide too much and cooking your Hydra! b. You should be able to focus on the tentacles. The cnidocytes will appear as swellings. c. Put on your goggles and add a small drop of methylene blue to the edge of the coverslip. Locate several cnidocytes with nematocysts coiled inside. d. Draw and label the bold terms above in your notebook. 8. Switch to the low power objective. Add a drop of 1% acetic acid to the edge of the coverslip and watch the rapid discharge of nematocysts from the cnidocytes. a. Using the high power objective study the discharged nematocysts. b. Draw and label the bold terms above in your notebook. 9. Complete the summary table provided, filling in all information for sponge characteristics in the appropriate row. Tape or paste this table into your notebook. You will be adding data over the next few lab exercises. 9