Study of the late embryogenesis of Daphnia (Anomopoda, 'Cladocera', Branchiopoda) and a comparison of development in Anomopoda and Ctenopoda

The embryonic development of Daphnia galeata and D. hyalina ('Cladocera', A nomopoda, Daphniidae) has been investigated by observing living embryos rem oved from female brood pouches. The sequence of morphological changes was a nalysed, as was the time at which the activity of certain organs began. The timing of these events at 22 degreesC is documented for both species. These data were compared with similar information, previously obtained for two representatives of the Ctenopoda (Kotov & Boikova, 1998). The sequence of events is basically similar in the two groups during early and late phas es of their development, but the time of shedding of the embryonic membrane s is different in the Anomopoda and Ctenopoda. The ctenopod embryo hatching from the second egg membrane is covered by the third membrane, which will be cast some hours later. The anomopod embryo hatches from the second egg m embrane approximately simultaneously with the shedding of the third membran e, and it is covered already by the fourth membrane after the shedding of t he second egg membrane. Earlier (Kotov & Boikova, 1998), we determined four embryonic instars in th e course of the development of the Ctenopoda. Two of them are passed within the egg membranes, the next two instars occur after the shedding the egg m embranes within the mother's brood pouch. However, in anomopods, one of the latter (the third) occurs within the second egg membrane, one is incorpora ted into the egg. Thus, the development of the Anomopoda is more embryonize d in comparison with that of the Ctenopoda.