Rotifers of the Great Lakes
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Approximately 275 species of rotifers have been reported for the Great Lakes. This partial list includes most of the planktonic (free-living) species. Great Lakes rotifers, particularly the soft-bodied forms have not been well studied. No data is included for Lake Superior rotifers.
Recent work indicates that rotifers may be important in packaging smaller material (e.g., by eating bacteria and detritus) into a form that is useful to higher organisms (e.g., larger crustacean zooplankton and larval fish). All rotifers have a corona of cilia surrounding their mouth. These cilia move rapidly setting up a current which draws food towards the rotifer mouth. However, they can be selective feeders - filtering out particles of the wrong size and actively rejecting certain particles using cirri. Once food has entered the rotifer mouth, it is ground by the trophi, plate-like structures which serve as teeth. Most species are omnivores, feeding primarily on bacteria and algae, a few are predatory, feeding on smaller rotifers and protozoa.
Rotifers in the Class Monogonata are normally diploid females which reproduce asexually (parthenogenesis). When conditions become poor (e.g., no food, temperature, crowding), these females produce 'mictic' female offspring. Mictic females produce haploid eggs which become males (which are haploid) if unfertilized, or, if a male is available to fertilize the egg (making it diploid again) a resting egg (which can remain dormant until conditions become favorable). Males are smaller than females, in some cases they may resemble the female, but usually they are reduced to a swimming reproductive organ, in many cases little more than a sperm sac with a tuft of cilia. Males generally live only a few hours (to days) dying immediately after reproduction. Rotifers in the Class Digonata are entirely amictic females, they apparently do not produce mictic females, males, or dormant eggs. Instead, the entire rotifer adult can survive extreme conditions by transforming to a resting stage.
|* ITIS separates Testudinellidae into 3 separate families: Filinidae (including Filinia), Testudinellidae (including Testudinella and Pompholyx) and Trochosphaeidae (including Trochosphaera). Stemberger places them all in a single family, and other references variously split them into 2 families.|
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