Meet the Porcelain Crabs: Ripley, Small, and the Alien Queen

Although not actually “true crabs” (they’re crustaceans, but from the family Porcellanidae) porcelain crabs resemble “real” crabs to a degree that most people can’t actually tell the difference.

16D05 Porcelain Crab on net

True crabs have eight walking legs, two pincers, and no antennae. By contrast, porcelain crabs have only six walking legs (their fourth pair of legs is much smaller, and normally held against the creature’s shell) and although they have crablike pincers, they also have a pair of long antennae, which originate near their eyestalks.

16D05 porcelain crab

Porcelain crabs have flat, round bodies–much like those of real crabs–which evolved over time to fit easily into crevices and under rocks–the creature’s preferred living quarters in the wild. You can find them living in almost every ocean (except the Arctic and Antarctic Oceans), but look carefully–the average porcelain crab has a body less than an inch in diameter. Some 277 species of porcelain crabs have been recorded, and fossils suggest the porcelain crab has been around since at least the Jurassic era.

In the wild, porcelain crabs are scavengers, feeding on detritus and using a pair of modified, feathery arms to strain plankton and other microscopic organisms from the water for food:

16D05 Porcelain Crab feeding

As peaceful, reef-safe creatures, porcelain crabs make excellent additions to home aquariums. They won’t molest (or eat) soft corals and don’t bother seahorses or other peaceful fish. They do show slight aggression toward other porcelain crabs (mostly a territorial issue) but my 60-gallon reef is large enough to keep three of them without any serious problems.

My oldest porcelain crab, Ripley, has lived in the reef for almost two years. During that time, she’s learned to recognize “feeding time” and will actually grab for the tube I use to put food (defrosted mysis shrimp) in the seahorses’ bowls. If she catches it, she’ll grasp the tube with one claw and use the other to pull out an armful of food. 

A couple of months ago, I introduced two other porcelain crabs to the reef. The smallest one, named “Very Small Creature” (a reference to “Very Small Beetle,” the smallest creature in the Hundred Acre Wood and one of my favorite characters in Winnie The Pooh), took up residence in a leather coral, probably mistaking it for an anemone:

16D05 porcelain crab in leather

The second new porcelain crab had no name at all for quite some time. Although I normally name any creature that I can tell apart from the others, nothing fitting came to mind. As it happens, Ripley solved that problem for me.

About a month after I placed the two new crabs in the tank, Ripley noticed the larger of the two new crabs sitting near her favorite coral. Wasting no time, Ripley made a rare trip across the tank, pulled off the new crab’s pincers (the crab is otherwise fine, and the pincers are already growing back) and then returned “home,” presumably having made her point to her satisfaction.

The new crab moved to another part of the tank–as proof of life, here’s a picture of her riding up the side of the tank on the back of one of my turbo crabs. She has her filter arms deployed, which makes it look as if she’s raising her “arms” in triumph:

16D05 porcelain crab and snail

What’s her name? 

Well, in my house, if Ripley rips your arms off on sight, and won’t tolerate you in her presence, clearly, you must be the Alien Queen. 

Have you ever seen, or owned, a porcelain crab? Are you a fan of crustaceans, or do they creep you out?