Why are cnidocytes useful as an evolutionary model in cell biology?

A. Cnidocytes are a unique to the Phylum Cnidaria and provide a model for the evolution of novel cell types across animals (Metazoa).
B. Numerous cnidocyte sub-types provide an opportunity to study mechanisms underlying cellular diversification by introducing homeotic mutations that recover ancestral phenotypes, aka atavism (Babonis, et al. 2023).
C. Expression of a polyanionic polymer (PGA) by bacteria and cnidocytes is evidence of horizontal gene transfer (HGT) from bacteria to an ancestral Metazoan (animal) that may have contributed to evolution of novel cell types in eukaryotes (Denker, et al. 2008).
D. All of the above.