Lasso cell (Zoöl.), one of a peculiar kind of defensive and offensive stinging cells, found in great numbers in all cœlenterates, and in a few animals of other groups. They are most highly developed in the tentacles of jellyfishes, hydroids, and Actiniæ. Each of these cells is filled with, fluid, and contains a long, slender, often barbed, hollow thread coiled up within it. When the cell contracts the thread is quickly ejected, being at the same time turned inside out. The thread is able to penetrate the flesh of various small, soft-bodied animals, and carries a subtle poison by which they are speedily paralyzed and killed. The threads, at the same time, hold the prey in position, attached to the tentacles. Some of the jellyfishes, as the Portuguese man-of-war, and Cyanea, are able to penetrate the human skin, and inflict painful stings in the same way. Called also nettling cell, cnida, cnidocell.