OSTRACODS OF BRITISH COLUMBIA

Cypricercus sp., scanning electron microscope photo by Gordon Green

by

Gordon Green

Royal BC Museum

Freshwater Ostracodes

Ostracodes are small crustaceans that abound in marine and freshwater habitats.  They are an important part of the benthic fauna of all freshwater habitats, occurring abundantly in temporary and permanent water bodies from roadside puddles to large lakes.

The ostracode's body is enclosed in a chitinous and calcitic bivalved carapace that is hinged along the dorsal margin.  The carapace can be tightly closed using adductor muscles that run through the body of the ostracode and attach to the inside of each valve.  When open, appendages of locomotion and feeding are extended from the ventral and anterior margins of the carapace. 

Some species swim in the water column, but most freshwater ostracodes are benthic, living at or near the sediment-water interface, crawling over or burrowing into the sediment. Others climb on aquatic vegetation in search of food.  Most ostracode species are herbivores or detritivores, feeding on diatoms, other algae and organic detritus. Carnivorous tendencies have been observed in a few species and many commensal forms are known, living primarily on the gills of crayfish. Locomotion is accomplished primarily by using the first and second antennae.  Species capable of swimming are characterized by antennae bearing long plumose setae.

Isocypris quadrisetosa, scanning electron microscope photo by Gordon Green.

Most species of freshwater ostracodes occur as adults only at certain times of the year.  Species living in temporary habitats such as vernal ponds have short life spans and are generally found only in the spring when rain fills otherwise dry depressions.  Before these habitats dry up in the summer ostracodes lay desiccation-resistant eggs that can survive the summer drought.  Adults of some species are able to survive extended periods of drought buried in the mud in a torpid state (Delorme & Donald 1969).  Species inhabiting permanent water bodies tend to have longer life spans beginning in the spring and extending for various lengths of time through the summer. 

Where conditions allow, some species survive through the winter.  McLay (1978) studied the ecology of four species of ostracodes in a temporary puddle and found that ostracodes appeared in the fall when the puddle filled with water and survived through the winter; a second generation appeared in the spring, matured and laid eggs before the puddle dried up in the summer.

Although the freshwater ostracode fauna of much of Canada has been studied (Delorme 1970 a-d, 1971) the ostracodes of British Columbia have received little attention. Basic information regarding taxonomy and distribution are lacking for this group of crustaceans and several collections have been made of undescribed species.

References

Delorme, L.D. 1970a. Freshwater ostracodes of Canada. Part I. Subfamily Cypridinae. Canadian Journal of Zoology 48:153-168

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

Delorme, L.D. 1970c. Freshwater ostracodes of Canada. Part III. Family Candonidae. Can. J.  Zool. 48:1099-1127

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

Delorme, L.D. 1971. Freshwater ostracodes of Canada. Part V. Families Limnocytheridae and Loxoconchidae. Can. J. Zool. 49:43-64.

Delorme, L.D. 1991. Ostracoda: in Thorp J.H. and A.P. Covich. Ecology and Classification of North American Freshwater Invertebrates. Academic Press. 911 pp.

Delorme L.D. and D.Donald. 1969. Torpidity of freshwater ostracodes. Can. J. Zool. 47:997-999.

Green, G.D. 1994. Freshwater Ostracoda (Crustacea) from the Southern Interior of British. Columbia. Royal British Columbia Museum. 38 pp.

McLay, C.L. 1978. Comparative observation on the ecology of four species of ostracodes living in a temporary freshwater puddle. Can J. Zool. 56:663-675.

McLaughlin, P.A. et al. 2005. Common and scientific names of aquatic invertebrates from the United States and Canada: Crustaceans. American Fish. Soc., Special Publication 31, Bethesca, Maryland.