Title photo Emperor shrimp on glossodoris nudibranch, by Ludovic
Above photo by Eric Cheng
-The Emperor Shrimp (Periclimenes imperator) is a species of shrimp with a wide distribution across the Indo-Pacific
Above, Nudibranch (Dermatobranchus ornatus), with Emperor Shrimp by Brian Mayes
-It lives commensally on a number of hosts (this is a long term symbiosis where one species gains benefits, while the other doesn't benefit, but is otherwise unharmed)
Above photo by EcoDivers1
-It will hitchhike on slow moving invertebrates including sea cucumbers, starfish (rare), molluscs...and also nudibranchs!
Above, Emperor shrimp on Nembrotha nudibranch by Roberta Cipressi
-The shrimp is only 19mm, and from it's vantage point it gains access to a stream of nutrients while perched on it's host
Photo by Jessie Weng
-The shrimps vibrant colours advertise the fact that it is unpalatable and help it camouflage on its host
Above, 'Ceratosoma tenue & Emperor Shrimp' by Allen Lee
Spot the shrimp.....Above, '(Jorunna funebris), actually two of them copulating. And an Emperor Shrimp...is attached!' photo by Ülar Tikk
-They also help by removing parasites and dead tissue from their host
Above, '(Periclimenes imperator) on a Glossodoris cincta Nudibranch' by Scott Rettig
Above, Tambja morosa with Periclimenes imperator by Benjamin Naden
-They live approx 2-3 years, and will often change hosts. Having a host is essential for the shrimps survival
Above photo by Brian Mayes 'I was surprised to see the shrimp change hosts and leave his small companion behind
-The shrimps are protandrous hermaphrodites. They are born with male reproductive organs and can change their sex to become female as they age and mature
Above photo by Georgette Douwma
-Finding a partner for reproduction can be complex as their dependence on their hosts can impact mating opportunities
Above, '(Periclimenes imperator) takes a ride on a Bumpy Mexichromis (Mexichromis multituberculata)' by David Guillemet
-After finding a suitable mate the female shrimp releases her eggs into the oceans current....
Above, 'Emperor shrimp on ceratosoma nudibranch' by KIYOSHI OKADA
-When the eggs hatch the small larvae will go through several life stages and molts, until eventually finding a companion to ride on....
Above photo by Brian Mayes
....reminds me of being sat on the sofa with my dog.....
Above photo by REINHARD DIRSCHERL
All info from wikipedia and also here and here
Above, 'Zenopontonia rex with Nembrotha milleri' by élanarchist
Above, '(Periclimenes imperator) with a Ceratosoma Tenue nudibranch as its commensal host' by Jun V Lao
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I'm not an expert, if there are any mistakes let me know in the comments and I'll edit my post!
....and on top of fornicating nudis, anything goes under the sea!