Chorionic fine structure of eggs from some species of Proboscidoplocia (Ephemeroptera, Ephemeroidea)

The genus Proboscidoplocia is endemic to Madagascar rind recent studies rev ealed that it is nor monospecific. The eggs of four newly described species . namely P billi. P. leplattenierae P. ruffieuxae and P. vayssierei, were i nvestigated by scanning and transmission electron microscopy. Eggs were fla ttened and showed two distinct sides joining along their peripheral border. In P. billi, a deep groove separated thr two sides. whereas only a slight rim was evident in the eggs of the other three species. Tile c chorionic de corations varied from irregular uplifted ribs, as in P. billi. to regularly arranged depressions. wider in P. leplattenierae (8-10 pm in diameter) tha n in P ruffieuxae (2-3 mum in diameter). In P vayssierei, the chorion showe d irregularly arranged micropores (about 1 mum in diameter). Mucous materia l covered the egg surface and tended to accumulate in the spaces between ri bs or inside the chorionic depressions. The chorion was formed by two layer s (endo- and exochorion) that showed a similar organisation of microcanals interposed between adjacent lamellae. In P. vayssierei. the presence of tun nels conferred a looser texture on the exochorion. Transmission electron mi croscopy images showed that both microcanals and tunnels opened on the egg surface. The superficial chorionic pattern was species-specific and the tex ture of both endo- and exochorion supported rhc conclusion of a close affin ity of these Malagasy species.