Title photo Emperor shrimp on glossodoris nudibranch, by Ludovic

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Above photo by Eric Cheng

-The Emperor Shrimp (Periclimenes imperator) is a species of shrimp with a wide distribution across the Indo-Pacific

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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)

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Above photo by EcoDivers1

-It will hitchhike on slow moving invertebrates including sea cucumbers, starfish (rare), molluscs...and also nudibranchs!

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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

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Photo by Jessie Weng

-The shrimps vibrant colours advertise the fact that it is unpalatable and help it camouflage on its host

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Above, 'Ceratosoma tenue & Emperor Shrimp' by Allen Lee

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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

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Above, '(Periclimenes imperator) on a Glossodoris cincta Nudibranch' by Scott Rettig

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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

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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

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Above photo by Georgette Douwma

-Finding a partner for reproduction can be complex as their dependence on their hosts can impact mating opportunities

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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....

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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....

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Above photo by Brian Mayes

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....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

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Above, 'Zenopontonia rex with Nembrotha milleri' by élanarchist

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Above, '(Periclimenes imperator) with a Ceratosoma Tenue nudibranch as its commensal host' by Jun V Lao

I'm not an expert, if there are any mistakes let me know in the comments and I'll edit my post!