Sea Urchin Communication

[klausi]

I am currently working on the covering behavior of sea urchins, and am filming them quite a bit, both in the lab and in the field. I have observed some instances where the urchins come together, and seem to interact (communicate?). The spines and tube feet touch and move around quickly, and the urchins remain close for a few minutes before one walks off again. It's hard for me to tell if these are just chance encounters, and the tube foot movement is simply their usual exploratory behavior, or if there is more to this.

These are Salmascis spaehroides and Tripneustes gratila.

Is there previous scientific work on this? Any anecdotal observations?

Here is a video I made about some urchin - urchin encounters: