Every month, the Rock Pool Project hosts tide pooling trips. Members visit the coasts around Cornwall in southeast England to see what critters are left in the rocky pools created when the tide goes out. On a trip last spring, Vicky Barlow picked up a rock and turned it over. To her surprise, she spied a rainbow sea slug!

These colorful creatures typically live in the warm waters off Spain, Portugal, and France. Only four have been spotted in the United Kingdom before. This one may have appeared because of warming ocean temperatures.