May 27, 2009
Commensal Coral Hermit Crab
I've acquired a new piece of coral with some interesting critters living inside. This piece is from Australia, I believe it is a Leptastrea pruinosa. The first thing I noticed about this tiny piece was the yellow commensal coral hermit crab, Paguritta sp. It measures about 3 mm total length. It is officially the smallest pet I've ever had. It is more yellow in real life, I'm still learning how to use this new camera. I've seen bigger ones, so I'm hoping it gets a lot of plankton to eat in my aquarium and grows. What really surprised me about this crab was that it was living in a Leptastrea coral. I've only ever seen them on SPS corals like Acropora, Montipora, and Astreopora corals.
I'm not sure how difficult these are to keep in captivity. Technically, these are filter feeders. If you click on the photo to enlarge it, you can see that the crab has feathery antennae that it uses to capture suspended plankton. Like its shelled hermit crab cousins, I've also seen it pick up tiny particles with its claws and put them in its mouth. Hopefully that means they will be easier to feed than other filter feeding animals.
When I looked closer at this coral, I noticed some tiny blue things with black markings. They are about half the size of the hermit crab. At first I thought they could be a different species of commensal coral hermit crab, but they didn't appear to have claws. I watched them during acclimation, but they didn't move much. Once I put the coral into my aquarium, I saw that the blue things lifted up and the tiny, feathery hand-like feeding apparatus of a barnacle came out of each one. There appears to be some tissue loss on this end of the coral, but I don't think it is a direct result of the barnacles living there. Click on the photos for larger views.
Update 6/20: I'm happy to say that my commensal coral hermit crab is doing well and is easy to feed. I target feed it daily with small pieces of frozen Mysis, Cyclops, and krill. Just like its shelled cousins, it holds the food (often several times the size of its body) in its claws, methodically rips small pieces off, and puts them in its mouth. It retreats when it detects movement nearby, but quickly comes out waving its arms and antennae when it senses food. I can get the tip of the syringe so close to the tiny crab that I can gently squirt pieces of food directly into its greedy claws. For good measure, I do often target some phytoplankton for its feathery antennae to catch.