protozoi giganti

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FOCUSXenophyophores

GRADE LEVEL7-8 (Life Science)

FOCUS QUESTIONWhat are xenophyophores and how do they inter-act with other species?

LEARNING OBJECTIVESStudents will be able to define and describe xeno-phyophores.

Students will be able to describe processes of feed-ing and locomotion in xenophyophores.

Students will be able to infer how xenophyophoresmay interact with other species in the biologicalcommunities of which they are part.

MATERIALS Materials for constructing a model xenophyophore

(styrofoam, modeling clay, gumdrops, toothpicks,stiff wire, etc.)

AUDIO/VISUAL MATERIALSNone

TEACHING TIMEOne or two 45-minute class periods, plus time forgroup research

SEATING ARRANGEMENTGroups of 4-6 students

MAXIMUM NUMBEROF STUDENTS30

KEY WORDSCold seeps

Methane hydrateClathrateXenophyophoreProtoctista

BACKGROUND INFORMATIONThe Blake Ridge is a large sediment deposit locatedapproximately 400 km east of Charleston, SouthCarolina on the continental slope and rise of theUnited States. The crest of the ridge extends in adirection that is roughly perpendicular to the conti-nental rise for more than 500 km to the southwestfrom water depths of 2,000 to 4,800 m. Over thepast 30 years, the Blake Ridge has been extensivelystudied because of the large deposits of methanehydrate found in the area. Methane hydrate is atype of clathrate, a chemical substance in which themolecules of one material (water, in this case) forman open lattice that encloses molecules of anothermaterial (methane) without actually forming chemi-cal bonds between the two materials.These depositsare significant for several reasons:

The U.S. Geological Survey has estimated thaton a global scale, methane hydrates may con-tain roughly twice the carbon contained in allreserves of coal, oil, and conventional naturalgas combined.

Methane hydrates can decompose to releaselarge amounts of methane which is a green-house gas that could have (and may already

Windows to the Deep Exploration

Giants of the Protozoa


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Windows to the Deep Grades 7-8 (Life Science)Focus: Xenophyophores oceanexplorer.noaa.gov

have had) major consequences to the Earthsclimate.

Sudden release of pressurized methane gasmay cause submarine landslides which in turn

can trigger catastrophic tsunamis. Methane hydrates are associated with unusual

and possibly unique biological communitiescontaining previously-unknown species thatmay be sources of beneficial pharmaceuticalmaterials.

In September, 2001, the Ocean Exploration DeepEast expedition conducted four DSV Alvin dives toexplore chemosynthetically-based communities onthe crest of the Blake Ridge at a depth of 2,154 m.

The expedition recovered some of the largest mus-sels (up to 364 mm) ever discovered, observedshrimp that appeared to be feeding directly onmethane hydrate ices, and documented 16 othernumerically abundant groups of invertebrates.

The expedition also observed a group of organismscalled xenophyophores (pronounced zee-no-FIE-oh-fors) that are neither animals nor plants, butare members of the kingdom Protoctista [Note: Weare using the five-kingdom scheme for classifying

living organisms rather than the three-domain,multi-kingdom scheme for reasons explained byMargulis and Schwartz (see Resources, below)].Almost all Protoctists are microscopic in size, butxenophyophores may be more than 20 cm indiameteryet they are composed of only one cell!Although xenophyophores are found throughoutthe worlds oceans, they are most abundant in verydeep waters beneath nutrient-rich surface water.Xenophyophores are easily damaged during col-lection and have not been cultured, so knowledge

about them is very limited. There are few internetsites that mention the phylum Xenophyophora (seeReferences, below). The most detailed description ofthese organisms is a monograph by Tendal (1972),but the discussion by Margulis and Schwartz(1998) is the most readily available. Some ency-clopedias also mention these organisms.

Like other protoctists, xenophyophores are believedto have evolved from symbiotic relationshipsbetween at least two different kinds of bacteria.The overall anatomy of xenophyophores consists

of masses of cytoplasm with multiple nuclei, sur-rounded by a branched tube system called agranellare which is made of a cement-like organicsubstance. Strings of fecal pellets, called stercomes,hang outside the granellare in masses called ster-comares. The granellare and stercomares are sur-rounded by a shell-like structure called a test that ismade of bits of minerals and the microscopic skel-etons of other organisms (e.g., sponges, forams,radiolarians). It is this foreign matter that givesxenophyophores their name: xenophyae (stranger

particles) + phore (bearer) = bearer of strangerparticles.

Xenophyophores can occur in densities of morethan 2,000 individuals per 100 m2, and are thedominant organism in some bottom communities.Their habit of stirring up bottom sediments to formtheir tests may be important to maintaining diver-sity. Another yet-to-be-explained observation is thatxenophyophores are often found in close associa-tion with ophiuroid echinoderms (brittle stars). The

2001 Ocean Exploration Deep East expeditionrecovered live xenophyophores from the edgeof the cold seep community on the Blake Ridge.Because xenophyophores have not been extensivelystudied, their importance to deep-sea biologicalcommunities is not knownbut this is not the sameas unimportant!

In this activity, students will gather information onxenophyophores, make a model based on theirresearch, and develop hypotheses about the role of

these organisms in deep-sea bottom communities.

LEARNING PROCEDURE1. Visithttp://oceanexplorer.noaa.gov/explorations/

deepeast01/logs/oct1/oct1.html and http://oceanexplorer.noaa.gov/explorations/03windows/

welcome.html for background on the 2001Ocean Exploration Deep East Expedition and


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oceanexplorer.noaa.govWindows to the Deep Grades 7-8 (Life Science

Focus: Xenophyophores

the 2003 Windows to the Deep Expedition tothe Blake Ridge. Lead an introductory discus-sion about these expeditions. You may alsowant to visithttp://www.bio.psu.edu/cold_seeps for a

virtual tour of a cold seep community in theGulf of Mexico.

2. Tell students that expeditions to deep-sea com-munities often lead to discoveries of new andunusual types of living organisms. Remindthem about the giant tubeworms of hydrother-mal vent communities which were completelyunknown until scientists visited them in person(visithttp://www.pmel.noaa.gov/vents/home.html formore information and activities on hydro-

thermal vent communities). Tell students thatamong the organisms found near cold seepcommunities on the Blake Ridge in 2001 werelarge (about 5 cm diameter) xenophyophores.Ask how many students have ever heard ofxenophyophores. Tell students that althoughthese are fairly common deep-sea organismsthroughout the worlds oceans, very little isknown about them. Tell students that they aregoing to find out as much as they can aboutxenophyophores, and develop their own

hypotheses about the role of these organismsin deep-sea bottom communities.

3. Have each student group prepare:a. A written report on xenophyophores that will

(at the minimum) include Explanation of what xenophyophores are Description of xenophyophores Explanation of how xenophyophores feed

and move around Description of interactions between xeno-

phyophores and other species in deep-seabottom communities

One or more hypotheses about the role ofxenophyophores in deep-sea bottom com-munities

[Note: An alternative to a traditional writ-ten report is to have students create a travelbrochure for a xenophyophore. Visit Travel

Brochure for a Cell by Mark Porter atwww.accessexcellence.org/AE/AEC/ AEF/1995/porter_

cell.html for a full description of this activity.]

b. A model of a xenophyophore illustratingwhat they have been able to learn aboutthese organisms. [Note: You may want tovisit String Cells by Marlys McCurdy atwww.accessexcellence.org/AE/AEC/ AEF/1995/mccurdy_

string.html for an alternative approach to con-structing a cell model.]

Have student groups begin their research bylooking for information on xenophyophoresin reference books (such as encyclopedias

and biology textbooks), as well as throughkeyword searches on the internet. Suggest thefollowing keywords:xenophyophoreprotoctistapodiaplasmodia

You may want to direct students to the follow-ing websites, or allow them to discover thesesites on their own:

levin.ucsd.edu/current_research/JMBAUK%20-%202001.pdf www.microscopy-uk.org.uk/mag/artnov98/xeno1.html

www.ngo.grida.no/wwfneap/Projects/Reports/ Offshore_

Features/xenophyophores.pdf

If students have trouble coming up withhypotheses, have them read Dressing upfor the deep: agglutinated protists adornan irregular urchin [available online atlevin.ucsd.edu/current_research/JMBAUK%20-%202001.pdf].This may give them some ideas, but they

should understand that xenophyophores mayhave many functions in their communities; atthis point, we just dont know.

4. Lead a discussion of what is known aboutxenophyophores. Have each student grouppresent their hypotheses about the role ofxenophyophores in deep-sea bottom com-


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Windows to the Deep Grades 7-8 (Life Science)Focus: Xenophyophores oceanexplorer.noaa.gov

munities, how these hypotheses are consistentwith current knowledge of these organisms,and what sort of investigations might be car-ried out to test their hypotheses. Ask students

whether they think it is worthwhile to studyorganisms like xenophyophores. Encouragepro and con discussion of this question, butbe sure to challenge students to defend theirpositions. At some point in this discussion,ask students whether unknown is the sameas unimportant. You may want to citeexamples in which obscure species proved tobe directly important to humans (such as theMadagascar periwinkle that provides a pow-erful cancer treatment).

THE BRIDGE CONNECTIONwww.vims.edu/bridge/ Enter cold seep in theSearch box, then click Search to display entrieson the BRIDGE website for cold seep communities.

THE ME CONNECTIONHave students write a short essay on how little-known or undiscovered organisms could be impor-tant to their own lives.

CONNECTIONSTO OTHER SUBJECTSEnglish/Language Arts, Earth Science

EVALUATIONWritten group reports and xenophyophore modelsprovide opportunities for assessment. In addition,you may want to have students write individualhypotheses about the role of xenophyophores indeep-sea bottom communities prior to the groupdiscussion in Step 4.

EXTENSIONSLog on to http://oceanexplorer.noaa.govto keep up to date with the latest Blake RidgeExpedition discoveries, and to find out what explor-ers are learning about cold-seep communities.

RESOURCEShttp://oceanexplorer.noaa.gov Follow the Blake Ridge

Expedition daily as documentaries and dis-coveries are posted each day for your class-

room use.

Van Dover, C.L., et al. 2003. Blake Ridge methaneseeps: characterization of a soft-sediment,chemosynthetically based ecosystem. Deep-Sea Research Part I 50:281300. (availableas a PDF file athttp://www.geomar.de/projekte/sfb_574/abstracts/vanDover_et_al_2003.pdf)

Margulis, L. and K. V. Schwartz. 1998. FiveKingdoms. W. H. Freeman, New York.

Tendal, . S. 1972. A monograph of the xenophyo-phoria. Galathea Report 12:7-103.

Levin, L.. A., A. J. Gooday, and D. W. James. 2001.Dressing up for the deep: agglutinated pro-tists adorn an irregular urchin. Journal of theMarine Biological Association of the UnitedKingdom 81:881-882. [available online atlevin.ucsd.edu/current_research/JMBAUK%20-%202001.pdf]

www.microscopy-uk.org.uk/mag/artnov98/xeno1.html A shortsummary of facts about xenophyophores,with a few references

www.ngo.grida.no/wwfneap/Projects/Reports/ Offshore_Features/

xenophyophores.pdf Part of a report thatincludes a discussion of xenophyophores inBritish waters

http://www.resa.net/nasa/ocean_methane.htm Links toother sites with information about methane

hydrates and associated communities

NATIONAL SCIENCE EDUCATION STANDARDSContent Standard A: Science As Inquiry

Abilities necessary to do scientific inquiry Understanding about scientific inquiry


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oceanexplorer.noaa.govWindows to the Deep Grades 7-8 (Life Science

Focus: Xenophyophores

Content Standard C: Life Science

Structure and function in living systems Diversity and adaptations of organisms

FOR MORE INFORMATIONPaula Keener-Chavis, National EducationCoordinator/Marine Biologist

NOAA Office of Exploration2234 South Hobson AvenueCharleston, SC 29405-2413843.740.1338843.740.1329 (fax)[email protected]

ACKNOWLEDGEMENTS

This lesson plan was produced by Mel Goodwin,PhD, The Harmony Project, Charleston, SC for theNational Oceanic and Atmospheric Administration.If reproducing this lesson, please cite NOAA asthe source, and provide the following URL: http://oceanexplorer.noaa.gov

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