Animal Kingdom - Coelenterata

Animals of phylum Coelenterata, or Cnidaria, are characterised in NCERT Class 11, Chapter 4 (Animal Kingdom) by the presence of stinging cells called cnidoblasts or cnidocytes located on the tentacles and the body surface. These cells contain organelles called nematocysts and are used for anchorage, defence and the capture of prey, which is why the phylum is named Cnidaria. Therefore cnidoblasts on the tentacles and body is the correct description. Choanocytes lining the spongocoel are features of sponges, Porifera, not coelenterates, so that option is wrong. Flame cells along the body wall belong to the excretory system of flatworms and are unrelated to any stinging function. Comb plates arranged in eight rows are the locomotory structures of Ctenophora, the comb jellies, not of Hydra. Coelenterates also exhibit tissue-level organisation, a central gastrovascular cavity with a single opening serving as both mouth and anus, and may show two body forms, the sessile polyp and the free-swimming medusa, in a phenomenon called metagenesis. A biological consistency check confirms the answer: immobilising prey by stinging is uniquely linked to cnidoblasts bearing nematocysts, and these are positioned where contact with prey occurs, namely the tentacles and body surface.