VARIABILITY OF FILTER STRUCTURES IN 8 DAPHNIA SPECIES - MESH SIZES AND FILTERING AREAS

The morphology of the filerting apparatus of eight Daphnia species (62 individuals of all size classes) was investigated by scanning electron microscopy. In the majority of animals the intersetular distances (= mesh sizes) showed a normal distribution and the mean values were between 0.2 and 1.0 .mu.m. The total filtering area increased approximately proportionally to the second power of the body length. Absolute values were between 0.063 and 2.6 mm2, with open portions of between 64% and 77% of the total area. In the relationship between mesh size and filtering area three types of allometric growth can be distinguished: (i) with increasing body length the mesh size remains small, but filtering area (FA) increases considerably (D. magna); (ii) both mesh size and FA increase with body length (D. pulicaria); and (iii) FA remains small but the mean mesh size becomes larger (D. cucullata).