Carcinoecium-Forming Sea Anemone Stylobates calcifer sp. nov. (Cnidaria, Actiniaria, Actiniidae) from the Japanese Deep-Sea Floor: A Taxonomical Description with Its Ecological Observations
Akihiro Yoshikawa, Takato Izumi, Taekya Moritaki, Taeko Kimura, Kensuke Yanagi
Summarized by Michael Hallinan
What data were used? 16 specimens of a new species of sea anemone (Stylobatus calcifer) were collected by beam trawl from Japan’s Sea of Kumano. All specimens were collected at a depth of 100 to 400m, with 6 of them being treated with ethanol immediately for DNA extraction. Most of the others were anesthetized and treated with a variety of chemicals for structural analysis, only one was further studied through behavioral observation prior to being treated with ethanol. In addition to the sea anemones, the shells used by the sea anemones and the symbiotic host hermit crabs were identified.
Methods: S. calcifer is a symbiotic species, it lives on the mollusc shells used by hermit crabs of the species Pagurodofleinia doederleini. The collected specimens were removed from the shells they were sitting on and dissected allowing for further analysis using different mixes of chemicals to help preserve and support the dissected parts during this series of observations. Following the visual observation, DNA was extracted from four of the specimens and compared to other species, with further comparisons to the most closely related species to analyze if the specimens found can be attributed to a new species. In addition to this qualitative data, a series of observations between one of the specimens and hermit crab were made in a seawater aquarium. These observations focused on recording the anemone’s interactions with the hermit crab, centered around the hermit crab’s shell, as well as what happened when a new shell was introduced. These observations were recorded and provided as supplementary material.
Results: S. calcifer was identified to be unique in its DNA, the shape of one of the muscles that manages openings in the anemone, direction of its mouth system, as well as the size distribution of its prey-capturing parts. However what sets it apart from previously known species even more is its symbiotic relationship and interactions with the hermit crab P. doederlein. Once the hermit crab discovered and moved into a new shell, it began to detach the sea anemone and encourage the sea anemone to transfer to the new shell through a series of pinches. There was no initial reaction from the sea anemone, but after about 43 hours from the hermit crab getting its new shell, the sea anemone has completed the transfer with it, mounting and covering the new shell. This allows the anemone to move across the seafloor by their hermit crab and collect food, while avoiding injury by being mounted on top of the shell. While symbiotic relationships between hermit crabs and sea anemones are known for over 30 other species, a hermit crab induced transfer to a new mollusc shell has never been observed until now.
Why is this study important? This study has expanded our understanding of taxonomy regarding sea anemones, but also provided a great observation of symbiosis between the hermit crab and anemone which not only allows us to better understand how both function but also opens the door for future research about the association between the two. All of this knowledge can better improve our ability to conserve as well as better understand relative biodiversity.
The big picture: A new species of sea anemone was discovered to have unique structural properties regarding its mouth and prey-capturing parts as well as a very unique symbiotic relationship with a hermit crab. The anemone is encouraged to transfer from shell to shell by the hermit crab. It mounts the shell inhabited by the crab as a means of transportation so it can acquire food easier. This new discovery allows us to better understand both respective organisms and their patterns but also conservation regarding both.
Citation: Yanagi, Kensuke (2022/04/01). Carcinoecium-Forming Sea Anemone Stylobates calcifer sp. nov. (Cnidaria, Actiniaria, Actiniidae) from the Japanese Deep-Sea Floor: A Taxonomical Description with Its Ecological Observations. The Biological Bulletin, 242, 127-152. doi: 10.1086/719160