I don't know why you're getting down voted. It's somewhat shocking to me that MDMA would have any kind of even slightly similar effect on such a wildly different animal.

Serotonin as a biological utility has been around since the beginning of multi-cellular life, maybe even sooner!

We organisms tend to share many of the same neurotransmitters. It's always pretty cool to observe similar pharmacological effects to those which humans experience as a result of a certain drug, and then watching a lobster react in a similar way!