Both mechanical and chemical stimuli cause
nematocysts to be discharged suggesting the involvement of both
chemoreceptors and mechanoreceptors in the discharge process
(Ozacmak et al., 2001). There is some controversy as to what causes
the explosion of the nematocysts. Picken and Skaer (1966) suggest a
sudden increase in permeability of the capsule wall while Lubbock
and Amos (1981) suggest that the explosion is initiated by an increase
in the osmotic pressure of the capsular fluid brought about by removal
of bound calcium ions. A number of studies have described in some
detail the discharge of nematocysts from nematocysts (Picken and
Skaer, 1966; Thurm et al., 2004; Tibballs, 2006).