Complex sentence: Stauromedusae, or the stalked jellyfishes, is an order of jellyfish within the Cnidaria phylum that are unique in that they do not enter the "medusa" stage, instead remaining polyps throughout their lives.
Split into simpler sentences: Stauromedusae, or the stalked jellyfishes, is an order of jellyfish within the phylum Cnidaria. They are unique in that they do not enter the "medusa" stage, instead remaining polyps throughout their lives.