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I study bioluminescence, but there are so many different species that I can't possibly study them all now at once.
One of my favorite groups of animals are the ostracods. They're tiny little crustaceans that are basically tiny shrimp shoved between two transparent shells kind of like an oyster. This first image here shows a fluorescence image of the animal. Its length is approximately 3mm on the longest axis.
In this next picture, I separated the little ostracod from its transparent clam-like shell. Again, this is a fluorescent image. The chitin and an associated small molecule that comprise the exoskeleton of the animal fluoresce green. If you looked at this animal in normal white light, you would only see the red pigment that the animal obtains from its diet.
See the little claw-like green things on the bottom of the animal? Those act like little oars that propel the animal around. They stick just far enough out of the shell to flap around in the water. These guys (and gals) swim fast! The only way to photograph them is to get them stranded in a tiny drop of water or shock them with cold water, alcohol, or fresh water.
Here's the shell without the animal inside. See those yellow spots that appeared on the left and right side of the animal? Those little fleshy, yellow-fluorescing spots appear in many Halocyprid ostracod species and are sometimes used for species identification. They occur near the mouth parts and near the anal bioluminescent gland. I think they might have some ecological function, but I have absolutely no evidence for that. What could they be for and what are they made of?!
Here's a view of the same shell, but I opened it like a book this time. Note the symmetry of the top and bottom portions. You can see how the yellow fluorescent spots match together when this shell is re-folded like a taco.
Thanks for looking at the ostracods! Still a mystery. Do you have any ideas what they use the fluorescent spots for?