Chitinous

In some colonial polyps, a chitinous periderm gives support and some protection to the connecting sections and to the lower parts of individual polyps.

The three phyla share four characters in common — chitinous cuticle, rings of scalids on the introvert, flosculi, and two rings of introvert retracts.

When discharged, it pierces the skin or chitinous exoskeleton of the prey and injects the poisonous fluid, hypotoxin, that either paralyzes the victim or kills it.