Fig. 1

Berghia stephanieae adult cerata, cnidosac, and select images of sequestered nematocysts. A Adult animal with many cerata found on the dorsum (Photo credit: Park Masterson). Box indicates the tip of the ceras, where the cnidosac is found. B Histological section of an adult B. stephanieae cnidosac (SIO-CIC M18637), including the cnidophages and sequestered nematocysts. Multiple nematocyst types are sequestered inside the adult B. stephanieae cnidosac, which are shown in (C) Differential Interference Contrast (DIC) imaging showing the shapes and sizes of various sequestered nematocyst types, and D Transmission Electron Microscopy (TEM) which shows the differences in internal morphology among nematocyst types. E The vacuole double membrane (arrow) surrounding individual nematocysts is also visible with TEM. Abbreviations: b, basitrich nematocysts; ce, cerata; cp, cnidophages; cs, cnidosac; ex, exit; m, musculature; mpm, large microbasic p-mastigophore nematocysts; mpa, microbasic p-amastigophore nematocysts; nem, sequestered nematocysts