Risbecia tryoni Nudibranchs

According to "Nudibranch Behavior" by David W. Behrens, this is called tailing, queuing or tailgating (No...really...tailgating). Most often seen in this species of Nudibranchs. Previously thought to be a prelude to mating, but that theory is now in question.

And that's your nudibranch lesson for today.