Photographs of gonadal structures illustrating the 5 stages of maturation identified for males (A-E) and females (F-J) of Senilia senilis: (A) and (F) early gametogenesis (stage 1), (B) and (G) active gametogenesis (stage 2), (C) and (H) ripeness (stage 3), (D) and (I) partial spawning (stage 4), (E) and (J) total spawning or rest (stage 5). Legends: ET empty tubule; H hemocyte; N nucleus; Nov non-mature oocyte; Mov mature oocyte; Rov residual oocyte; Spg spermatogonia; Spc spermatocyte; Spz spermatozoid; T tubule.