Teaching the major invertebrate Phyla in one laboratory session.
Abstract: This one-session laboratory exercise teaches all the major invertebrate phyla in about 2 hours.

Key Words: Invertebrate; evolution; biodiversity; laboratory.
Subject: Biological diversity (Study and teaching)
Invertebrates (Study and teaching)
Education (Methods)
Laboratory schools
Author: Davis-Berg, Elizabeth C.
Pub Date: 05/01/2011
Publication: Name: The American Biology Teacher Publisher: National Association of Biology Teachers Audience: Academic; Professional Format: Magazine/Journal Subject: Biological sciences; Education Copyright: COPYRIGHT 2011 National Association of Biology Teachers ISSN: 0002-7685
Issue: Date: May, 2011 Source Volume: 73 Source Issue: 5
Geographic: Geographic Scope: United States Geographic Code: 1USA United States
Accession Number: 265291891
Full Text: In many survey classes, such as general biology, marine biology, or life sciences, covering the major invertebrate phyla can become a time sink. I have developed a laboratory exercise in which students examine the Porifera (sponges), Cnidaria (jellyfish, etc.), Annelida (worms), Mollusca (snails, clams, etc.), Arthropoda (insects, crabs, etc.), Brachiopoda (lamp shells), Echinodermata (brittle stars, urchins, etc.), and Chordata (tunicates) in one session. This multistation laboratory uses a combination of preserved and live specimens, slides, and images to present samples of each phylum. The exercise is designed to take advantage of an aquarium in the classroom but does not require one. Students answer questions and sketch what they observe at one or two stations per phylum. The lab takes approximately 2 hours with a 20-minute setup, and students are able to see the vast diversity among these phyla and understand the similarities and differences across the groups. I have found this laboratory to be effective in teaching the invertebrate phyla in a course when time is a limiting factor.

** Course Context

This laboratory exercise was created for my marine biology course but can be applied to any class that includes biodiversity. This is an introductory, nonmajors class and can be taken at any point during the students degree program. The course takes place over a 15-week semester, each week consisting of a 3-hour combination lecture and laboratory block. Typically, there are 80 students enrolled in the course in four sections of 20 students each. Students' majors are all from arts and communication fields such as film, journalism, fiction writing, art, and music.

** Rationale: Incorporating Evolution When Teaching Biodiversity

The majority (~95%) of animals on the planet are invertebrates (Anderson, 2001). If only the vertebrates are covered, students will not have an understanding of the evolutionary spectrum of animal diversity. Invertebrates have many different body plans and ways to complete the basic needs of life, including feeding, reproduction, and dispersal. In addition, many students have never learned about the subphylum Urochordata (sea squirts/tunicates) and are under the mistaken impression that all chordates have a back bone. This laboratory exercise helps to put the diversity of animals in perspective for the students.

The National Science Education Standards for K-12 students (National Research Council [NRC], 1996) ask that students understand that "the great diversity of organisms is the result of more than 3.5 billion years of evolution that has filled every available niche with life forms." In addition, students need to understand that "biological classifications are based on how organisms are related. Organisms are classified into a hierarchy of groups and subgroups based on similarities which reflect their evolutionary relationships" (NRC, 1996). These standards continue at the college level in the Bio2010 plan for biology undergraduates (NRC, 2003).

It is imperative to teach evolutionary relationships when teaching biodiversity. This reinforces evolutionary concepts preceding the laboratory. Without an understanding of the basic evolutionary framework, students will simply memorize facts and be unable to understand how organisms are connected. There are a variety of resources available for teachers of evolution, including Tree of Life (http://www.tolweb.org), Understanding Evolution (http://evolution. berkeley.edu), National Center for Science Education (http://www. ncse.com), and the PBS Evolution site (http://www.pbs.org/wgbh/ evolution/index.html).

** Objectives

The objectives of this laboratory are to (1) be able to recognize to which phylum an animal belongs, (2) learn the evolutionary relationships of the invertebrate phyla, and (3) understand the process of evolution at the phylum level (i.e., sponges have evolved even if they appear to be morphologically similar to fossil sponges).

** Teacher Procedures

When teaching this laboratory, I always present recent phylogenies of the animal kingdom. Textbooks are often behind in incorporating the latest phylogenic hypotheses, and this can be used to further discussion on the nature of science. I frequently consult the Tree of Life website to learn more about recent research. This past semester, I used the recent paper by Schierwater et al. (2009) to show my students contemporary thinking about animal relationships. Schierwater et al. (2009) found that the Placozoa are at the base of the metazoa, rather than the Porifera or sponges (Figure 1). I used this to stimulate an inclass discussion prior to this laboratory to talk about the differences between the new phylogeny and the one presented in the text (Figure 1; Castro & Huber, 2008). This discussion focused specifically on how these differences reflected different evolutionary relationships among these organisms.

In this exercise, 10 stations are set up in order on the tables in the classroom (Table 1). Each station is labeled with the station number, phylum name, a short description of the phylum, and diagrams (copied, labeled, and cited) from various invertebrate textbooks (e.g., Anderson, 2001) to assist with answering questions. If specimens are not available, I typically will get photographs or other images to augment the preserved and live material. I also provide video of animals such as sponges if living organisms are not available. I use one or two microscopes per station for my 20 students, but that can be varied easily, depending on class size or facilities.

In the classroom, we have a 60-gallon marine tank that is stocked with invertebrates and some fishes from the Gulf of Mexico. I have the students observe the tank during the laboratory (Figure 2). Additional specimens include living organisms, dried sponges, coral skeletons, and organisms in jars. Preserved specimens were purchased from Carolina Biological Supply (http://www.carolina.com) or Ward's Natural Science (http://www.wardsci.com), and living organisms were obtained from Gulf Specimen Biological Supply (http://www. gulfspecimen.org) or Ward's.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

** Student Procedures

In this laboratory, you will rotate from station to station (untimed), observing several specimens from each of eight phyla. As you move around the room, think about what taxonomists value in placing certain organisms together: why are the organisms at each station more similar to each other than to those at other stations? Try to imagine how you would classify a brand new, heretofore undiscovered organism - what physical or behavioral traits would you look at first when trying to classify it? With these questions in mind, let's move on to the phyla.

** Assessment & Discussion

This lab exercise is a great way to present the invertebrate phyla in a few hours. Students get to explore the material and work independently or in groups as they learn. The students complete most of the laboratory in class and then turn it in with completed questions the following week. The questions and material presented can be modified for any classroom setup and budget. Setup can take around 20 minutes, so I prepare the stations ahead of time and then move them into the classroom just before lab. It is helpful to have all the microscopes focused and ready to go.

Assessment on the material from this laboratory will appear on the final exam in the class. I ask my students for feedback on all laboratory exercises at the end of the course and always get positive reviews. This exercise will take 2 hours to complete, and students do not like for it to be split across multiple weeks. The adjunct faculty enjoy teaching this exercise and find that students leave with a better understanding of the invertebrate phyla.

I use select questions (in italics in Table 1) to focus on the evolutionary principles covered in the lab. After the labs are graded and returned, as a class we have a discussion about those questions, focusing on commonly missed items for that section. We also will look again at the phylogenies during this discussion and go over remaining questions about the material. The in-class discussion is very important in helping students understand the big picture of the animal kingdom.

DOI: 10.1525/abt.2011.73.5.7

** Acknowledgments

I thank Gerald Adams, Joshua Berg, Cynthia Gerstner, Daniel Jordan, and Brittan Wilson for their comments on the manuscript. I also thank my students at Columbia College Chicago, and instructors Michele Hoffman and Mark Wollschlaeger, who helped me refine this laboratory.

References

Anderson, D.T., Ed. (2001). Invertebrate Zoology. Oxford, UK: Oxford University Press.

Castro, P. & Huber, M. (2008). Marine Biology, 7th Ed. New York, NY: McGraw Hill.

National Research council. (1996). National Science Education Standards. Washington, D.c.: National Academy Press.

National Research council. (2003). Bio2010: Transforming Undergraduate Education for Future Research Biologists. Washington, D.c.: National Academics Press.

Schierwater, B., Eitel, M., Jakob, W., Osigus, H.-J., Hadrys, H., Dellaporta, S.L. & others. (2009). concatenated analysis sheds light on early metazoan evolution and fuels a modern "Urmetazoon" hypothesis. PLoS Biology, 7(1), e1000020.

ELIZABETH c. DAVIS-BERG is Assistant Professor of Science and Mathematics at columbia college chicago, 600 S. Michigan Ave., chicago, IL 60605; e-mail: edavisberg@colum.edu.
Table 1. Station setup and questions
(those in italics focus on evolutionary principles).

   Station          Setup at Station          Questions for Students

Station 1:      Mixed spicule slide        1. Sketch the slide,
Porifera                                      remembering to label the
                                              spicules:
                                           2. What do you think the
                                              spicules are made of?
                                              Why?
                                           3. How would you test the
                                              hypothesis that spicules
                                              deter predators? How
                                              might a sponge that
                                              lacks spicules (like a
                                              bath sponge) protect
                                              itself?

Station 2:      Commercial sponge          1. Look at the slide of
Porifera        slide                         the commercial sponge.
                Preserved sponges in          Label the ostia (holes).
                jars                       2. There are two samples
                Living sponges (in tank)      of commercial sponges:
                                              living (in the tank) and
                                              preserved. Sketch the
                                              two, paying close
                                              attention to the
                                              differences between them.
                                           3. What changes do you
                                              think take place between
                                              living and deceased
                                              versions of the same
                                              species?
                                           4. Questions for later:
                                              Sponges seem very
                                              different from other
                                              animals. Why are they
                                              still classified as
                                              metazoans? Is it true
                                              that they haven't
                                              evolved in millions of
                                              years?

Station 3:      Medusae jars               1. Sketch the Obelia
Cnidaria        (cnidaria set)                medusa (pelagic form)
                Obelia Medusae slide          and label the bell,
                Deerhorn coral skeleton       mouth, and tentacles.
                Brain coral skeleton       2. What are contained
                                              within the tentacles?
                                              What is their function?
                                           3. Look at the skeleton
                                              of the deerhorn coral
                                              and the live sea whip
                                              in the tank.
                                           4. What do both of these
                                              (soft and hard coral)
                                              have in common? Why do
                                              you think they are
                                              shaped the way they are?

Station 4:      Obelia whole mount         1. Sketch the Portuguese
Cnidaria        slide                         man of war tentacle,
                Portuguese man of war         labeling the nematocysts.
                slide                      2. Do you see a pattern
                                              of how the nematocysts
                                              are distributed?
                                           3. Why is the man of war
                                              dangerous to humans?
                                           4. Look at the Obelia
                                              whole-mount slide and
                                              draw it--label the
                                              feeding tentacles and
                                              reproductive structures.
                                           5. Would you recognize
                                              this as the same animal
                                              you saw in the Obelia
                                              medusa slide
                                              (Station 3)?
                                              Why or why not?

Station 5:      Annelida jar collection    1. Looking at the
Annelida        Worm x-s slide                collection of preserved
                                              and living worms--what
                                              features do they all
                                              have in common?
                                           2. Sketch the slide of
                                              the worm in
                                              cross-section,
                                              remembering to label the
                                              blood vessels,
                                              intestine, and muscles.
                                           3. Worms have a closed
                                              circulatory system--what
                                              advantages do you think
                                              it provides for the
                                              worms?
                                           4. What do the
                                              polychaetes use to
                                              move?
                                           5. Many polychaetes that
                                              live in tubes decorate
                                              them with debris that
                                              they find around them.
                                              Why do you think they do
                                              this? What do you think
                                              the costs are to the
                                              organism? What are the
                                              benefits?

Station 6:      Mollusks jar collection    1. Looking at the
Mollusca        Mussel gill slide             collection of mollusks,
                                              what do you see as
                                              common features across
                                              the group?
                                           2. Sketch the slide of
                                              the gill and label blood
                                              vessels and the gill.
                                           3. Why does the gill have
                                              so many layers?
                                           4. What is the function
                                              of the gill?
                                           5. Look in the tank--we
                                              have snails, slugs,
                                              oysters, and chitons.
                                              Pick one and draw it.
                                           6. What behavior do you
                                              see the snails doing
                                              while you are watching
                                              the tank? What do you
                                              think they eat? Why?

Station 7:      Arthropoda jar             1. Look at the collection
Arthropoda      collection (marine only)      of preserved and living
                Hermit crab (in tank)         crustaceans--what
                Barnacles (in tank)           features do they all
                                              have in common?
                                           2. Sketch a hermit crab,
                                              taking care to label
                                              eyes, mouth, legs,
                                              claws, and shell.
                                           3. What do you observe
                                              the crabs doing?
                                           4. Where do they get
                                              their shells?
                                           5. The barnacles in the
                                              tank are arthropods; how
                                              would you recognize
                                              that?
                                              Do you see any common
                                              features?
                                           6. Question for later:
                                              Compared to mollusks,
                                              arthropods are much more
                                              diverse on land than in
                                              the water. Insects
                                              (bugs) are very
                                              abundant. What
                                              do you think helped the
                                              arthropods become so
                                              successful on land?

Station 8:      Preserved mussel in jar    1. Draw the brachiopod
Mollusca vs.    Preserved brachiopod          and the mussel:
Brachiopoda     in jar                     2. What external
                                              differences do you see?
                                           3. Look at the diagrams
                                              at the station--what
                                              other differences are
                                              there?
                                           4. Why am I making you
                                              draw all these animals?
                                              Am I just being cruel or
                                              is there something I am
                                              hoping that you will
                                              learn by drawing instead
                                              of looking at pictures?
                                              (Hint: while cruelty may
                                              indeed play a role,
                                              there just might be
                                              other factors to
                                              consider.)

Station 9:      Preserved echinoderms      1. After looking at the
Echinodermata   in jars                       echinoderms, please list
                Living echinoderms in         the common features that
                tank                          you see.
                                           2. In the tank, look at
                                              the brittle stars and the
                                              sea stars--what
                                              differences do you see
                                              between them? Brittle
                                              stars tend to eat
                                              detritus, whereas sea
                                              stars are predators. They
                                              are also in separate
                                              classes within the
                                              phylum.
                                           3. Sketch and label
                                              brittle stars and sea
                                              stars, paying close
                                              attention to their
                                              differences.
                                           4. The sea urchins and
                                              sea cucumbers look
                                              different from the sea
                                              stars and brittle stars.
                                              What features do each of
                                              them have that identify
                                              them as echinoderms?

Station 10:     Preserved tunicates in     1. Look at the preserved
Chordata        jars                          tunicates--how do you
                                              think this organism
                                              feeds?
                                           2. Draw a tunicate.
                                           3. Question for later:
                                              Which features make this
                                              group part of the
                                              chordates? Can you see
                                              them in the adult?
                                           4. Question for later:
                                              What modifications do you
                                              think the predator
                                              tunicate that we saw in
                                              class a few weeks ago has
                                              for eating prey instead
                                              of filter feeding?
                                           5. Question for later:
                                              List one thing you liked
                                              about this lab, one thing
                                              you didn't, and give me a
                                              suggestion on how to
                                              change it for next year.
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