So, lobsters.

"If a dominant lobster is badly defeated, its brain basically dissolves. Then it grows a new, subordinate’s brain — one more appropriate to its new, lowly position. Its original brain just isn’t sophisticated to manage the transformation from king to bottom dog without virtually complete dissolution and regrowth."

"In one of the more staggering demonstrations of the evolutionary continuity of life on Earth, Prozac even cheers up lobsters."