Efferent mechanisms of discharging cnidae: I. Measurements of intrinsic adherence of cnidae discharged from tentacles of the sea anemone, Aiptasia pallida

Two kinds of cnida predominate in the tentacles of the acontiate sea anemones: spirocysts and microbasic mastigophore nematocysts. These cnidae discharge in response to appropriate mechanical and chemical stimulation. In this paper, we calculate the strengths of attachment between the tentacle and the capsules (= "tentacle adherence") of discharged spirocysts and mastigophores by measuring adhesive force and by determining the numbers of spirocysts and mastigophores discharged onto targets under conditions where the attachment of everted cnida tubules to the target (= "cnida adhesion") exceeds tentacle adherence. Under these conditions, the average contribution of individual cnidae to adhesive force is called the intrinsic adherence. The intrinsic adherence is a measure of the average frictional force required to dislodge the capsule of individual discharged cnidae from the tentacle. The intrinsic adherence of discharged mastigophores varies inversely, from 0.45 to 0.15 mgf (4.41 to 1.47 μN), with the number of discharged mastigophores. The larger values characterize mastigophores discharged by mechanically triggering nonchemosensitized tentacles, whereas the lower values characterize the intrinsic adherence of mastigophores discharged from chemosensitized tentacles. In contrast, the intrinsic adherence of discharged spirocysts is very low to insignificant. Thus, by comparison to mastigophores, spirocysts contribute little, if any, to adhesive force, and, by inference, do not directly secure captured prey to the tentacle. Our measurements indicate that penetrable prey are primarily secured to the tentacle by discharged mastigophores and by the inherent stickiness of the tentacle surface.