I have not read up much on D. sessilifolia, however; if it is a close match for D. burmannii, it probably also uses "snap tentacles" to perform quick protective movements around it's prey. The outer ring of long tentacles with elongated glands that do not produce dew are the "snap tentacles" and are purported to keep ants from stealing prey from the plant. You can observe this movement by using a toothpick to stimulate one of the outer tentacles and time the response. D. spatulata also possesses "snap tentacles" that I have timed at about 15-20 seconds.