The freshwater zooplankton are comprised of three major groups of invertebrate animals: the rotifers, copepods, and cladocerans. The rotifers constitute a phylum found almost exclusively in freshwater (Wallace and Snell, 1991) and are not included in the photos of this web site. The copepods and cladocerans are both groups of the large subphylum Crustacea. Copepods constitute a class which is widespread in both freshwater and marine environments. Cladocerans constitute a group of four orders living primarily in freshwater environments. All three of these major groups have species adapted to pelagic (open water), or littoral (vegetated), and benthic (bottom) environments. The reader can find detailed descriptions of the biology of cladocerans and copepods in Dodson and Frey (1991) and Williamson (1991), respectively. These sources also provide information on sampling, culturing, identification techniques, and include a good review of literature on these groups.
Dodson and Frey (1991) and Williamson (1991) also include keys to identification. The keys for the copepods and cladocerans go only as far as the genus level. Keys to species can be found in Edmondson (1959), which is widely used by professionals. Since taxonomy is a dynamic science, names of some groups have changed with time; thus a widely-scattered primary literature is also used by professionals. The college text by Pennak (1989) also includes keys to species.
To identify zooplankton requires use of a compound microscope. A dissecting microscope is also handy for sorting and counting. Specimens are mounted on glass slides and examined at 25-100X magnification. Comparison of your animal with an image, whether a photo (this web site) or line drawings (in taxonomic keys), is only a first step to identification. In order to identify your animal to species requires that you consult one or more of the above-cited sources, learn some anatomical terminology, and follow the keys. However, you can develop an eye for certain characteristics useful for discriminating species by examining your animal under the microscope (best) and by referring to photos in this web site. In particular, consider the following traits. What is the general body shape? (Try drawing the outline of the body.) What is the color? Opaque or translucent? Examine the relative length of appendages (e.g. antennae, legs) and setae (hair-like processes). Notice presence and relative size of spines. For more-detailed descriptions of taxonomically-useful anatomy, refer to Dodson and Frey (1991) and Williamson (1991).
Also notice the size of your animal. Notice that, in the photos in this web site, we have included a scale bar with each image. Using the scale bar, you can better compare the relative size of species with each other. Taxonomic keys often include questions about size. Determining size may seem tricky at first, but it is basically like using a ruler in everyday life. You need to know the scale of your ruler and then match it with items of interest. The standard ruler for a microscope is called an "ocular micrometer", which is fitted into the eyepiece of your microscope. In lieu of a micrometer, you can use the diameter of the field. Each of these methods requires that you first standardize your microscope against a ruler of known length; at low magnification, this standard could be a transparent office ruler, but at higher magnifications a stage micrometer is needed. Be aware that different microscopes are not exactly the same and the size goes down with increased magnification. For example, my microscope at 100X has a field diameter of about 1,500 μm, but at 250X this diameter is 450 μm.
Dodson, S.I., and D.G. Frey. 1991. Cladoceran and other Branchiopoda. Pp. 723-786 in Thorp, J.H., and A.P. Covich (eds.). Ecology and classification of North American freshwater invertebrates. Academic Press, San Diego.
Edmondson, W.T. (ed.). 1959. Freshwater biology. Wiley.
Pennak, R. 1989. Freshwater invertebrates of the United States. Wiley, 3rd edition.
Thorp, J.H., and A.P. Covich. 1991. Ecology and classification of North American freshwater invertebrates. Academic Press, San Diego.
Wallace, R.L., and T.W. Snell. 1991. Rotifera. Pp. 187-248 in Thorp, J.H., and A.P. Covich (eds.). Ecology and classification of North American freshwater invertebrates. Academic Press, San Diego.
Williamson, C.E. 1991. Copepoda. Pp. 787-822 in Thorp, J.H., and A.P. Covich (eds.). Ecology and classification of North American freshwater invertebrates. Academic Press, San Diego.
Benzie, J.A.H., 2005. Cladocera: The Genus Daphnia (including Daphniopsis) (Anomopoda: Daphniidae). Backhuys Publishers, Leiden. 368 p.
Berner, D.B. 1986. Taxonomy of Ceriodaphnia (Crustacea: Cladocera) in U.S. Environmental Protection Agency cultures. EPA/600/4-86/032.
Berner, D.B. 1987. Significance of head and carapace pores in Ceriodaphnia (Crustacea, Cladocera). Hydrobiologia 145: 75-84. (Ceriodaphnia)
Brandlova, J., Z. Brandl, and C.H. Fernando. 1972. The Cladocera of Ontario with remarks on some species and distribution. Can. J. Zool. 50: 1373-1403. (Ceriodaphnia)
Brooks, J.L. 1957. The systematics of North American Daphnia. Mem. Conn. Acad. Arts & Sciences 13: 1-180.
Brooks, J.L. 1959. Cladocera. Pp. 587-656 in Edmondson, W.T. (ed.) Freshwater Biology. Wiley.
DeMelo, R. and P.D. N. Hebert. 1994. A taxonomic reevaluation of North American Bosminidae. Can. J. Zool. 72: 1808-1825.
Dodson, S.I., and D.G. Frey. 1991. Pp. 723-786 in Thorp, J.H., and A.P. Covich (eds). 1991. Ecology and classification of North American freshwater invertebrates. Academic Press. (Up to date keys to genera; particularly useful for chydorids.)
Dumont, H.J. & S.V. Negrea. 2002. Introduction to the Class Branchiopoda. Backhuys Publishers, Leiden, Belgium. 398 p.
Dumont, H.J. and J. Pensaert. 1983. A revision of the Scapholeberinae (Crustacea: Cladocera). Hydrobiologia 100: 3-45.
Frey, D.G. 1959. The taxonomic and phylogenic significance of the head pores of the Chydoridae (Cladocera). Inter. Rev. ges. Hydrobiol. 44: 27-60.
Frey, D.G. 1961. Differentation of Alonella acutirostris (Birge 1879) and Alonella rostrata (Koch 1841) (Cladocera: Chydoridae) Trans. Amer. Micros. Soc. 80: 129-140.
Goulden, C.E. 1968. The systematics and evolution of the Moinidae. Transactions of the American Philosophical Society. NS. 58 (6): 1-101.
Hann, B.J. 1981. Occurrence and distribution of littoral Chydoridae (Crustacea, Cladocera) in Ontario, Canada, and taxonomic notes on some species. Can. J. Zool. 59: 1465-1474.
Hebert, P.D.N. 1995. Version 1 (unpublished): The Daphnia of North America--An Illustrated Fauna. (CD-ROM).
Hudson PL, Reid JW, Lesko L, T., Selgeby JH. 1998. Cyclopoid and Harpacticoid Copepods of the Laurentian Great Lakes. Ohio Biological Survey: Columbus, OH.
Hudson PL, Lesko L, T., Bowen CA, II, Poly WJ, Chriscinske MA. 2003. Parasitic copepods and branchiurans of the Laurentian Great Lakes. Ann Arbor, MI: Great Lakes Science Center Home Page: http://www.glsc.usgs.gov/greatlakescopepods/Key.asp?GROUP=Parasite.
Hudson PL, Lesko L, T., Reid JW, Chriscinske MA. 2003. Cyclopoid copepods of the Laurentian Great Lakes. Ann Arbor, MI: Great Lakes Science Center Home Page: http://www.glsc.usgs.gov/greatlakescopepods/Key.asp?GROUP=Cyclopoid.
Korinek, V. 1981. Diaphanosoma birgei n.sp. (Crustacea, Cladocera). A new species from America and its widely distributed subspecies Diaphanosoma birgei ssp. lacustris n.ssp. Can. J. Zool. 59: 1115-1121.
Korovchinsky, N.M., 1992. Sididae and Holopediidae (Crustacea: Daphniiformes). Backhuys Publishers, Leiden. 82 p.
Lesko L, T., Hudson PL, Chriscinske MA. 2003. Calanoid copepods of the Laurentian Great Lakes. Ann Arbor, MI: Great Lakes Science Center Home Page: http://www.glsc.usgs.gov/greatlakescopepods/Key.asp?GROUP=Calanoid.
Lesko L, T., Hudson PL, Reid JW, Chriscinske MA. 2003. Harpacticoid copepods of the Laurentian Great Lakes. Ann Arbor, MI: Great Lakes Science Center Home Page: http://www.glsc.usgs.gov/greatlakescopepods/Key.asp?GROUP=Harpacticoid.
Megard, R.O. 1967. Three new species of Alona (Cladocera, Chydoridae) from the United States. Int. Rev. gesamten Hydrobiol. 52: 37-50.
Michael, R.G. and D.G. Frey. 1983. Assumed amphi-Atlantic distribution of Oxyurella tenuicaudis (Cladocera, chydoridae) denied by a new species from North America. Hydrobiologia 106: 3-35.
Negrea, S. 1983. Fauna Republicii Socialiste Romania. Crustacea. Volume IV. Fascicula 12. Cladocera. Editura Academiei Republicii Romania. Bucuresti. 399p. (Simocephalus)
Pennak, R.W. 1989. Freshwater Invertebrates of the United States. Third ed. J. Wiley and Sons, Inc., New York.
Rivier, I.K., 1998. The Predatory Cladocera (Onychopoda: Podonidae, Polyphemidae, Cercopagidae) and Leptodorida of the World. Backhuys Publishers, Leiden. 213 p.
Smirnov, N.N. 1996. Cladocera: the Chydorinae and Sayciinae (Chydoridae) of the World. SPB Academic Publishing, Amsterdam. 197 p.
Smirnov, N.N. 1971. Chydoridae Fauny Mira. Fauna SSSR. Nov. Ser. No. 101. Rakoobraznyye. Vol. 1, vyp. 2. (Available in English from Israel Program for Scientific Translations, Jerusalem, 1974).
Smirnov, N.N.,1992.The Macrothricidae of the World.Backhuys Publishers, Leiden. 151 p.
Williamson, C. E. 1991. Copepods. Pp. 787-822 in Thorp, J.H., and A.P. Covich (eds). Ecology and classification of North American freshwater invertebrates. Academic Press, New York. (Up to date keys to genera.)
Wilson, M.S. 1959. Calanoida. Pp. 738-795 in Edmondson, W.T. (ed.) Freshwater Biology. Wiley.
Wilson, M.S., and H.C. Yeatman. 1959. Harpacticoida. Pp. 815-861 in Edmondson, W.T. (ed.) Freshwater Biology. Wiley.
Yeatman, H.C. 1959. Cyclopoida. Pp. 796-814 in in Edmondson, W.T. (ed.) Freshwater Biology. Wiley.
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Last RevisedAugust 2006
The Zooplankton Project was conceived by Drs. John Havel and Russell Rhodes in 1998.
Webmaster for the Zooplankton Project is Erin Hutchison