The feeding mechanisms of the Daphniidae (Crustacea: Cladocera): recent suggestions and neglected considerations

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Abstract
While the importance of grazing by anomopod cladocerans of the family Daphniidae on crops of planktonic algae and bacteria, and on detritus, is widely recognized, and although many calculations have been made on the filtering rate of these crustaceans, the feeding mechanisms involved in these processes have frequendy been misinterpreted by ecologists. Recent accounts that purport to describe the feeding mechanism of Daphnia are based on misinterpretations of morphology and are completely erroneous. The ancestors of daphniids were probably benthic, littoral animals, similar in various respects to primitive represcritatives of extant chydorids and macrothricids. The feeding mechanisms of the latter give useful indications of the kind of device from which that of the daphniids probably arose. The daphniid mechanism was derived by restricting particle abstraction to trunk limbs 3 and 4. Contraiy to recent claims, mink limbs 1 and 2 are not involved in this element of the feeding process. Comparative studies on many anomopods reveal invariable correlations. Species employing currents to cany food particles have filter plates bearing filtratory setules. Species that, for whatever reason, do not employ currents, except sometimes for respiration, have homologous structures that lack filtratory setules, even when, as is often the case, they feed on particulate matter. Comparisons with other branchiopods are also helpful.

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