Body length, size of resting eggs and identification of the ephippia of Ceriodaphnia megalops and Ceriodaphnia pulchella

Abstract

The ephippia of Ceriodaphnia megalops and Ceriodaphnia pulchella are described. Their ephippia may be identified by their size and shape, supplemented by measurement of the length of the resting egg. The ephippia are shed free in the water and float by means of a special area of gas-filled tissue. Each ephippium contained one ellipsoid resting egg. The length, width and shape of the resting eggs of both species were investigated, and comparisons made with published data of their parthenogenetic eggs. For both species the volume of a resting egg was virtually the same as the volume of a parthenogenetic egg, but the resting egg was more elongated. The shape of resting eggs was linearly related to egg volume on logarithmic axes in a manner similar to that reported for the parthenogeneticeggs of these two species. The linear relationship between total parthenogenetic egg volume and body length reported for these two species did not apply to their resting eggs.

Ephippia of the Daphniidae (Branchiopoda: Cladocera) in Late Caenozoic deposits: untapped source of information for palaeoenvironment reconstructions in the Northern Holarctic

“…3). Few cases of successful discrimination of Ceriodaphnia species using ephippia were made previously (Bottrell, Newsome, 1976;Berner, 1985), but our recent investigation confirmed that at least main species groups of Ceriodaphnia could be identified based on ephippial morphology under both optical and scanning electron microscope .…”