Because I'm sure you all wanted to know more
Since we were talking about echinoderm develoment, I of course had to spend time trying to find pictures of the "tumor-like" adult on the larvae (although technically I believe it's called a juvenile rather than adult). I couldn't find great pictures online although I know they exist (I haven't figured out the best search terms it seems). The first pic is of a young pluteus (sea urchin larvae). The second is of an older pluteus. See the brown growth? That's the juvenile which will attach, reabsorb all of the larval features and crawl off to become an adult. The old plutei are so strange looking with these brown outgrowths which wave around small tube feet and spines. Unfortunately this picture does not convey the bizarreness of it all and how it just looks so very wrong.