An amazing symbiotic relationship in the deep sea

A new species of sea anemone has been discovered off the coast of Japan by a research team led by Dr. Yoshikawa from the University of Tokyo. The sea anemone, newly named Stylobates calcifer, lives in a symbiotic relationship with the hermit crab Pagurodofleinia doederleini. The anemone occupies the entire top of the hermit crab’s shell, attaching itself by means of a hard shell-like secretion called a carcinoecium. This phenomenon isn’t new to science as approximately 35 species of anemones have mutually beneficial relationships with hermit crabs. However, in their study “Carcinoecium-forming sea anemone Sylobates calcifer sp. nov. (Cnidaria, Actiniaria, Actiniidae) from the Japanese deep-sea floor: a taxonomical description with its ecological observations,” published in the April 2022 issue of The Biological Bulletin, in addition to identifying and naming a new species, the scientists were also able to closely observe and describe the animals’ behavior when the hermit crab changes shells, thereby extending knowledge of their natural history and how symbiosis is maintained.

In a series of first ever live recordings of the living state, the crab can be observed attempting to urge the anemone, still attached to the old shell, to detach and move to occupy its new shell. It alternatively taps and pinches the anemone with its walking legs and chelipeds. Although no apparent reaction was initially observed by the sea anemone, its position was gradually moved and peeled off from the shell by the intense efforts of the hermit crab. After about 43 hours from the host’s shell change and 18 hours from detachment from the old shell, the sea anemone began to mount and completely cover the new shell. It was positioned on the shell with tentacles facing upward, to enable feeding on suspended particulate matter from the water column and detritus from the hermit crab’s feeding. The researchers suggest that the benefit to the hermit crab includes safety from parasites and predators that could affect its growth or shorten its life.

The species name calcifer assigned by the authors is derived from the novel Howl’s Moving Castle and the Japanese animated film of the same name. Calcifer is the name of a fire demon that helps the wizard Howl build his castle, attesting to the sea anemone’s ability to construct its own shell-like secretion.

The Biological Bulletin disseminates novel scientific results in broadly related fields of biology in keeping with more than 100 years of a tradition of excellence. The Bulletin publishes outstanding original research with an overarching goal of explaining how organisms develop, function, and evolve in their natural environments. To that end, the journal publishes papers in the fields of Neurobiology and Behavior, Physiology and Biomechanics, Ecology and Evolution, Development and Reproduction, Cell Biology, Symbiosis and Systematics. The Bulletin emphasizes basic research, including articles on marine model systems and those of an interdisciplinary nature.