The predator Polyphemus pediculus has a fearful look because of the eye which is extremely large compared to the rest of the body. It is one of the most common cladocerans in Norway and may occur in high numbers in the littoral.
Species from the family Polyphemidae are very different from other cladocerans and are therefore easy to identify. The predator Polyphemus pediculus has a compact form and its eye is extremely large compared to the rest of the body, and takes up most of the head. The carapace is only covering the brood chamber, and not the postabdomen and the feet. By growth, the offspring comes out when the enveloping cuticle finally ruptures. P. pediculus is the only species of this family in freshwater. Its colour varies, often with different varieties of yellow but grey and violet are also common.
Female: Length 0.7–1.8 mm
Male: Length 0.7–1.0 mm
Ecology and distribution
P. pediculus is one of the most common cladocerans in Norway. It may occur in high numbers in the littoral and is also found in the zooplankton. It occurs in about 60 % of the investigated water bodies and is slightly more common in lakes than in ponds. The frequency of localities with P. pediculus, decrease slightly with increasing altitude. The highest record is from a small lake situated 1444 m a.s.l. It has a wide tolerance to differences both in pH and conductivity.
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