Fig. 3. Nematocyst discharge in Polykrikos.

(A) The putative ballistic sequence of nematocyst discharge is as follows: (1) striated capsule contracts; (2) internal pressure forces stylet to pierce capsule and open operculum (dark green); (3) part of the capsule everts; (4) stylet exits through the nozzle and detaches; and (5) mucilaginous tubule (blue) uncoils and is projected through the stylet base (yellow). Orange, relaxed capsule wall; red, contracted capsule wall. (B to E) SEM micrographs of isolated discharged nematocysts (B to D) and a nematocyst piercing a prey cell (E). Arrowhead, operculum; C, capsule; T, tubule.