Eggs of the assassin bug genus Sinea have an expansion of the chorion called the corolla that gives the eggs a flower-like appearance. In 2016, corollae of S. rileyi Montandon were observed to open and close in the laboratory, prompting a study on the morphology and mechanism of this movement. Eggs of field-collected S. complexa Caudell, S. diadema (F.), S. integra Stål, and S. rileyi were used to complete various portions of this study. Significant differences in the size of the corollae were found among species, with the greatest area for S. diadema, the least for S. complexa, and intermediate for S. riley and S. integra. The volume of the eggs of S. diadema was significantly greater than those of the other three species. The major components of the corollae and adjacent structures are defined and were found to differ among species. Confocal microscopy revealed structural differences in regions of the corollar rim and portions of the operculum. Corollae reacted to water similarly for all species but varied in reaction time. The mechanism of corollae movement is discussed. Results suggest that the reaction of the corolla is a purely physical property of the chorion and that this movement could be a means of water regulation for the developing embryo.