The reader can find detailed descriptions of the biology of ostracodes in Meisch (2000) and Delorme (2001). These sources also provide methods for collection and sorting, identification keys, and include a good review of literature on these groups. The keys in Delorme (2001) go to the genus level. The keys in Tressler (1959) go to species level and are still widely used by aquatic biologists, although some of the taxonomy has since changed. The recent book by Meisch (2000) has excellent descriptions of European species, many of which are also found in North America. Other keys for North American species found in Canada are available in Delorme (1967) and detailed descriptions are available in Delorme (1970a-d, 1971). Earlier monographs by Furtos (1933) and Hoff (1942) give excellent drawings of species collected from Ohio and Illinois, respectively. In this web site, we follow the higher taxonomy as shown in Delorme (2001).

The ostracodes have a rich fossil history (Schram 1986), and paleontologists can identify species solely on shell characteristics. These traits include size and shape in lateral view, breadth (thickness), and a number of “ornaments”, such as pustules, teeth, grooves, pittings, and muscle scars (Meisch 2000, Delorme 2001). Such features can be readily seen in scanning electron micrographs, such as those shown in Delorme (1971, 2001). Many of these shell features can also be seen in wet mounts, which can also reveal color. We used wet mounts in the current web site. Taxonomic keys also include details of structures seen on the limbs, and thus their use requires dissection and a familiarity with anatomy.

A dissecting microscope is useful for sorting and counting. A compound microscope may be needed for identification. Some species can be identified solely by shell characteristics. However, many must be dissected in order to see the limbs. Specimens are first placed in a viscous liquid, such as glycerine or Hoyer’s solution, and dissected directly on a glass slide. Shells are removed and placed next to the visceral mass before adding a cover slip. Then the entire preparation can be examined at 100-400X magnification.

Comparison of an animal with an image, whether a photo (this web site) or line drawings (most taxonomic keys), is only a first step to identification. In order to identify the ostracode to species requires that one consults the above-cited sources, learns some anatomical terminology, and then follows the keys. However, one can develop an eye for certain characteristics useful for discriminating species by examining the animal under the microscope 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 as seen from the side.) Also examine the shape when placed on its edge—is it rotund or thin? What is the color? Opaque or translucent? Can any shell ornamentations be seen? Look for differences in shape and size between females and males (sexual dimorphisms), such as depicted in Hoff (1942) or Tressler (1959). Some species are sexual (so males will be present), whereas other are strictly asexual, with populations consisting solely of females (Delorme 2001). Sexual dimorphisms are illustrated in the key of Kesling (1956). For more-detailed descriptions of taxonomically-useful anatomy, see Kesling (1956), Tressler (1959), or Delorme (2001).

Also notice the size of the animal. Most freshwater ostracodes range in size from about 0.5 – 1.0 mm, which are barely visible with the naked eye. However, some species are considerably smaller (e.g., entocytherids) or larger (e.g., Megalocypris). For photos in this web site, we have included a scale bar with each image. Using the scale bar, one 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 the 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 the microscope. In lieu of a micrometer, one can also estimate size using the diameter of the microscope 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 mm, but at 250X this diameter is 450 mm.

Literature cited

Delorme, L.D. 1967. Field key and methods of collecting freshwater ostracodes in Canada. Canadian Journal of Zoology 45: 1275-1281.

Delorme, L.D. 1970a. Freshwater ostracodes of Canada. Part I: Subfamily Cypridinae. Canadian Journal of Zoology 48: 153-169.

Delorme, L.D. 1970b. Freshwater ostracodes of Canada. Part II: Subfamilies Cypridopsinae, Herpetocypridinae, and family Cyclocyprididae. Canadian Journal of Zoology 48: 253-266.

Delorme, L.D. 1970c. Freshwater ostracodes of Canada. Part III: Family Candonidae. Canadian Journal of Zoology 48: 1099-1127.

Delorme, L.D. 1970d. Freshwater ostracodes of Canada. Part IV: Families Ilyocyprididae, Notodromadidae, Darwinulidae, Cytherideidae, and Entocytheridae. Canadian Journal of Zoology 48: 1251-1259.

Delorme, L.D. 1971. Freshwater ostracodes of Canada. Part V: Families Limnocytheridae, Loxoconchidae. Canadian Journal of Zoology 49: 43-64.

Delorme, L.D. 2001. Ostracoda. Pp. 811-849 in Thorp, J.H., and A.P. Covich (eds.). Ecology and classification of North American freshwater invertebrates. Academic Press, San Diego. 2^nd edition.

Furtos, N.C. 1933. The Ostracoda of Ohio. Ohio Biological Survey, Vol. 5, Bulletin 29: 413-524.

Hoff, C.C. 1942. The ostracods of Illinois, their biology and taxonomy. Illinois Biological Monograph 19: 196 p.

Kesling, R. V. 1965. Anatomy and dimorphism of adult Candona suburbana Hoff. Four Reports of ostracod Investigations. Report 1. University of Michigan Press, Ann Arbor. 56pp.

Meisch, C. 2000. Freshwater Ostracoda of Western and Central Europe. Süßwasserfauna von Mitteleuropa 8/3. Spektrum Akademischer Verlag. Heidelberg.

Schram, F.R. 1986. Crustacea. Oxford University Press, New York.

Tressler, W.L. 1959. Ostracoda. Pp. 657-734 in Edmondson, W.T. (ed.). Freshwater biology. Wiley, New York.

Web site posted: January 2005

John Havel and Elissa Dey