<P> In addition to epitheliomuscular, nerve and interstitial cells, the inward - facing gastroderm ("stomach skin") contains gland cells that secrete digestive enzymes . In some species it also contains low concentrations of cnidocytes, which are used to subdue prey that is still struggling . </P> <P> The mesoglea contains small numbers of amoeba - like cells, and muscle cells in some species . However, the number of middle - layer cells and types are much lower than in sponges . </P> <P> Polymorphism refers to the occurrence of structurally and functionally more than two different types of individuals within the same organism . It is a characteristic feature of Cnidarians, particularly the polyp and medusa forms, or of zooids within colonial organisms like those in Hydrozoa . In Hydrozoans, colonial individuals arising from individuals zooids will take on separate tasks . For example, in Obelia there are feeding individuals, the gastrozooids; the individuals capable of asexual reproduction only, the gonozooids, blastostyles and free - living or sexually reproducing individuals, the medusae . </P> <P> These "nettle cells" function as harpoons, since their payloads remain connected to the bodies of the cells by threads . Three types of cnidocytes are known: </P>

Name the two forms of polymorphism in cnidarian