PLATE 1 (Figures 5–7): The different gonad maturity stages of Potamopyrgus antipodarum: a) digestive gland; b) 1st order secondary oocyte; c) secondary mature oocyte; d) germinating center; e) digestive tube; f) embryos; g) mantle; h) foot; i) albumen gland; j) kidney; k) nephridial gland; l) oviduct; m) mucus gland; n) embryonic sac; o) mature oocyte; arrow: primary oocyte; Lu: light of digestive tube

Figure 5: A): Transversal cut of a P. antipodarum gonad (primary vitellogenesis) B): Primary Vitellogenesis.