New Species of Green-Eyed Crab Has An Odd Home: A Coat of Live Animals

This hermit crab (Sympagurus dimorphus) is closely related to the green-eyed hermit crab, and both live in symbiosis with anemone-like creatures. Charles Griffiths

This is the story of the green-eyed hermit crab, and it's coat of many creatures. Most hermit crabs live in shells not of their own making, taking the cast-offs of clams, shellfish and the like. But this newfound species of hermit found off the west coast of South Africa takes a different path: It lives within a colony of living, anemone-like animals. (Anemones are ornate polyps with tentacles used to catch and feed on small fish and the like.)

The new species was discovered during a survey of life on the seafloor during a research cruise in 2013, but was only fully described in a study published recently in the journal ZooKeys. The most striking feature of the crab, dubbed Paragiopagurus atkinsonae, is its green eyes. Why does it have green eyes? Nobody knows.

The green-eyed hermit crab (Paragiopagurus atkinsonae), sans its anemone "shell." Landschoff and Lemaitre / ZooKeys

The relationship between the anemones, which contain stinging tentacles and the crab is a symbiotic one: The former provides a home for the latter, and the latter presumably helps provide food for the former, as well as a moving substrate on which to cement themselves. When the crab has been rudely removed from its anemone coat, you can see that it has a light orange coloration throughout, and a small curled tail that initially gives rise to a small shell, but which is subsequently covered in anemones. The bodies of the animals themselves reach a length of less than three inches.

The anemones are technically called zoanthids, and unlike more commonly-known sea anemones live in colonies rather than singly. The crab resides within a collection of zoanthids in the genus Epizoanthus (genus is the taxonomic classification above species). These creatures "glue" themselves together with an amalgam called a carcinoecia that contains bits of sand and organic material.

These green-eyed wonders were found within a very small area of the ocean floor, between about 650 and 900 feet below the surface. That was a little odd to the researchers because there didn't appear to be anything unique about this spot. "The area isn't noticeably biologically or oceanographically distinct, but more detailed sampling from the area will tell us more about the habitat conditions," says Jannes Landschoff, a University of Cape Town doctoral candidate who authored the paper along with Smithsonian Institution researcher Rafael Lemaitre, in a statement. "Future studies need to take this into account and give the area more research attention."

"Incidents like these are flags for future protection," Landschoff added. "The bottom line is we know so little about these offshore habitats from an ecological point of view."

A closeup of Paragiopagurus atkinsonae's green eyes. Landschoff and Lemaitre / ZooKeys