Sanibel shell curiousity

While walking along one of the beaches on Sanibel Island, Florida, I found a Lightening Whelk shell in shallow water which appeared to have at least two other animals tightly wrapped around it. The whelk did not appear to be alive, but the other animals did, so I decided to take some iPhone photos and return it to the waters where I found it.  Initially I thought the bright orange fibrous strands were something tangled, but then observed that they were tightly anchored and part of these animals.  The photos show the strands coming from the spots on the animals.  I am curious what these animals are, and if they are eating the shell itself, or are using it for some other purpose.

As an aside, this poses a sort of chicken & egg problem:  Because I am not particularly familiar with sea-life, I do not have the appropriate keywords or phrases to find answers to my questions using current language based search technology.  It is intriguing to envision image based search technology that would allow finding pictures of similar creatures and thus information about them!

After a note to the folks at The Bailey-Matthews Shell Museum on Sanibel, I received the following helpful response:

The two animals wrapped around that lightning whelk shell are sea anemones. The orange strands are defensive threads produced by the sea anemone. The single shell attached to the whelk seems to be a common slipper shell.

So, now I have the answer and a pointer toward further inquiry. That the threads are a defensive mechanism probably explains the slight stinging sensation that I’ve had in my fingers…don’t go tugging on something you don’t know anything about!