Porcelain Crabs and Squat Lobsters are neither true crabs nor true lobsters; they are actually Galatheoids, and are more closely related to hermit crabs. Most of the tiny squat lobsters and porcelain crabs you’d find as hitchhikers or for sale at your LFS are reef safe and peaceful. They are best kept singly or in pairs in nano tanks, as they may fight with their own or similar species, but given enough territory, multiples can be housed together.
Crinoid squat lobsters, Allogalathea elegans and Galathea inflata, make their homes on Crinoid feather sea stars for protection. Crinoids are believed to have an unpleasant taste or toxin and are rarely eaten by predators. Crinoid squat lobsters also obtain food from their hosts; these kleptoparasites use their chelipeds (claws) to comb food from the Crinoids’ feathery arms. Crinoids are nearly impossible to keep in captivity, but Crinoid squat lobsters do not require a host to thrive in a home aquarium if they are target fed plankton and meaty foods like frozen mysis and copepods. Their coloration is as variable as their hosts, though the most common colors are black, white, and yellow. Most Crinoid squat lobsters are smooth, but some are spiny, further helping to blend in with their host. A. elegans can be distinguished from the nearly identical G. inflata by having a longer rostrum that extends far past the eyes.
One other squat lobster – the stunning scarlet red Galathea balssi – is infrequently offered in the aquarium hobby. It grows slightly larger than the Crinoid squat lobsters and has no symbiotic relationships. Other free-living Galatheids found as hitchhikers make fine pets. Squat lobsters are typically drab brown or gray, but some of the coral symbionts have striking colors and patterns.
Three similar species of Porcelain crabs in the genus Neopetrolisthes live on anemones like E. quadricolor, bubble tip anemones. They are white with varying brown dots and spots. They feed on mucous and food particles that fall into the anemone’s tentacles and also use their filter feeding setae to sift plankton from the water. They protect their anemone from small predators, but you should use caution when housing porcelain anemone crabs and clownfish together. If the clownfish decide to live in the anemone, they usually evict the porcelain crabs.
There are dozens of free-living and coral symbiont species in the genus Petrolisthes. Many can be found as hitchhikers and a few are readily available in the aquarium trade. They’re usually gray or purple, but some very brightly colored specimens are occasionally found.
The squat lobsters and porcelain crabs most often encountered by hobbyists are hardy and adapt well to life in aquariums, but like other crustaceans, they are sensitive to copper, nitrates, and changes in salinity and water quality. Avoid aggressive tank mates or those large enough to consume them.
All photos by author unless otherwise noted. Photo captions and credits, left to right:
Gallery 1: Allogalathea elegans on purple Crinoid; Galathea inflata on Crinoid; White and yellow Crinoid Squat Lobster; Galathea Balssi, Photo with permission by Justine Hughes Ostrowski, All rights reserved; Photo by Ratha Grimes, CC BY 2.0 https://www.flickr.com/photos/ratha/17285435165/; Galathea inflata Crinoid Squat Lobster, note the short rostrum; black and white Crinoid Squat Lobster; Crinoid Squat Lobster in Crinoid eating frozen mysis; Photo by Akuppa John Wigham, CC BY 2.0 https://www.flickr.com/photos/90664717@N00/1464427318;
Gallery 2: Porcelain Anemone Crab on Rose Bubble Tip Anemone; “Purple Zebra” Bolivian Porcelain Crab; Porcelain Crab; Photo by Christian Gloor, CC BY 2.0 https://www.flickr.com/photos/christian_gloor/11019792676/; Photo by Christian Gloor, CC BY 2.0, https://www.flickr.com/photos/christian_gloor/25911687430/; photo by Tam Warner Minton, CC BY 2.0, https://www.flickr.com/photos/travels_with_tam/28288489240/; Porcelain Anemone Crab on E. quadricolor