All nematocysts have a solid, elastic wall and a lid
structure, which closes the capsule before discharge. The lid
can be shaped as a solid operculum in hydrozoans or it can
consist of three opercular flaps in anthozoans (Godknecht
and Tardent,1988). In the discharged form, all capsules have
a pear- or banana-shaped capsular body with an extended
twisted tubule that normally carries three rows of spines.
The tubule morphology of capsules differs considerably
among cnidarian species, but the capsules of the highest
structural complexity are found in hydrozoans. Here, the
stenoteles represent one of the most sophisticated capsule
types. The stenotele tubule is enlarged at its basal region,
which is called the shaft. The distal shaft carries the stylet
apparatus, which contains three huge stylets and three
arrays of thinner spines. This stylet apparatus forms a dart
when the tubule evaginates, which punches a whole into
the prey’s cuticle through which the long tubule enters,
releasing hemolytic and neurotoxic substances (Tardent,
1995). The dart-like stylet apparatus can penetrate even
thick crustacean cuticles