|MadSci Network: Zoology|
I am not exactly sure if I have the answer to your question, but I have an idea. Sea anemones have nematocysts, with which they sting and kill their live prey (they also receive nutrition from byproducts of algae living on their oral disks). There are species of fish, known either as anemone fish or clown fish, which can live among the tentacles of the sea anemone unharmed. The key to this relationship between fish and anemone is mucus. Scientists believe either that the fish coat themselves with the anemone's mucus, making the fish "look" chemically similar to the anemone, or that the fish chemically modify their own mucus to match the anemone. In either case, the mucus coating the fish chemically mimics the mucus coating the anemone, and the fish can swim among the tentacles unharmed. So if the fish can prevent attack from the anemone by matching mucus, I would imagine that the tentacles are protected from each other by a similar mechanism.
Check out the following sites for more information on sea anemones and clownfish:
Friends and Anemones
Actinians and Their Fish
Hope this helps!
Ingrid Dodge, Mad Scientist
Try the links in the MadSci Library for more information on Zoology.