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Family Polyphemidae
Polyphemus pediculus (Linnee, 1761)
P. pediculus was found in ten lakes and one pond spanning the study area. Samples were collected at a depth of 30.5 m to the surface, varying in temperature from 16.5° C to 23° C. Conductivity did not exceed 215 mS/cm. Occurring over a pH range of 6 to 7.6 from sites in the study area, P. pediculus has been previously reported from pH 4.1 to 9.5 (Berzins and Bertilsson, 1990; Sprules, 1978). Substrate varied from mud to a mixture of mud and rock The sole representative of the family Polyphemidae in North America, P. pediculus is a visually guided predator feeding on protozoans, rotifers and smaller cladocerans (Balcer et al., 1984; Brooks, 1959; Odselius and Nilsson, 1983). During daylight this distinctive cladoceran shows a preference to the upper strata of lakes where light levels are sufficient for seeking prey, migrating to deeper depths only during periods of intense light (Butorina, 1986; Odselius and Nilsson, 1983). Laboratory experiments show that P. pediculus is negatively phototactic in a strong beam of light but becomes positively phototactic when the light intensity decreases (Hutchinson, 1967). More abundant in nearshore waters, this holarctic species often forms large mushroom-shaped swarms which are concentrated in the upper water strata. Scattered in patches throughout the water body, the distribution of these aggregations may be related to availability of food (Balcer et al. 1984; Butorina, 1986).P. pediculus is easily recognized by its globular brood chamber, enlarged compound eye which almost fills the head, and elongated abdomen ending in two long caudal setae. Collection Localities: Lightning Lake 983-663-1; Coquihalla Lakes 995-67-1; Lambly Lake 992-75-7; Nicola Lake 983-830-5; White Lake 994-147-7; Pavilion Lake 984-58-2,989-214-4; Caribou Lake 983-255-2; Thuya Lake 994-227-1; pond Hwy 5 S. of Clearwater 994-234-6; Star Lake 994-229-1,994-231-6,994-232-1; Azure Lake 983-54-2. Cladocerans of the Thompson-Okanagan Region |
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