Cnidarians are commonly recognized as sea jellies, corals, or complex colonies such as the Portuguese man-of-war. While some cnidarians possess rigid internal calcareous skeletons (e.g., corals), many are soft-bodied. Intriguingly, genes coding for the chitin-biosynthetic enzyme,chitin synthase(CHS),were recently identified in the model anemoneNematostella vectensis,a species lacking hard structures. Here we report the prevalence and diversity of CHS across Cnidaria and show that cnidarianchitin synthasegenes display diverse protein domain organizations. We found thatCHSis expressed in cnidarian species and/or developmental stages with no reported chitinous or rigid morphological structures. Chitin affinity histochemistry indicates that chitin is present in soft tissues of some scyphozoan and hydrozoan medusae. To further elucidate the biology of chitin in cnidarian soft tissues, we focused onCHSexpression inN. vectensis. Spatial expression data show that threeCHSorthologs are differentially expressed inNematostellaembryos and larvae during development, suggesting that chitin has an integral role in the biology of this species. Understanding how a non-bilaterian lineage such as Cnidaria employs chitin may provide new insight into hitherto unknown functions of polysaccharides in animals, as well as their role in the evolution of biological novelty.