Two New Anemones Discovered in Coral Reef Caves

February 3, 2015 / Japan, Asia
This is a single polyp of Palythoa umbrosa under stereomicroscope.

This is a single polyp of Palythoa umbrosa under stereomicroscope. Scale = 0.5 cm. Photo by Yuka Irei

Two new species of encrusting anemones have been found in shallow caves and cracks of Coral Reefs in the Pacific Ocean.

In research published last week in the open access journal ZooKeys, scientists from the University of the Ryukyus in Okinawa, Japan described the new species.

The two species belong to the genus Palythoa, which is commonly found on shallow coral reefs in subtropical and tropical waters worldwide.

One of the dominant benthic organism on shallow coral reefs, their success may in part be due to their ability to host zooxanthellae—symbiotic, photosynthetic, single-celled algae that can provide host species with energy from the sun—while also being efficient planktonivores. Surprisingly, unlike almost other known Palythoa species, the two new species do not have zooxanthellae.

Found in the shallow caves and cracks of coral reefs off the coasts of Okinawa and New Caledonia, the new species also appeared to be unique in their habitat preference.

One of the species is described from just in front of a landfilled reef coastline on Okinawa Island and it is encouraging to see that there is still some unknown biodiversity just in front of our door. Dr. Frederic Sinniger, JAMSTEC

Palythoa mizigama is found in Okinawa Island, Japan.

Palythoa mizigama is found in Okinawa Island, Japan. Photo by Yuka Irei

At first, we were surprised at the discovery of specimens, and thought we had one undescribed and unusual species on our hands, but we were even more surprised when DNA analyses showed clearly that there were two different species. Yuka Irei, University of the Ryukyus Graduate Student

Further research by Irei and Reimer in Okinawa revealed additional minor morphological differences between the two species.

These two species are morphologically very similar, with long tentacles to acquire plankton from the water column, and polyps that are curved towards the entrances of cracks or caves for better access to their food source. James Davis Reimer, University of the Ryukyus Associate Professor

While genetically distinct, each species appears to have evolved very similar features to adapt to its life in the dark.

These two species provide an excellent example of parallel evolution, as each evolved independently from each other. The only reliable way to tell the two species apart asides from DNA are the patterns and markings on their tentacles. Yuka Irei, University of the Ryukyus Graduate Student

Palythoa are usually colonial, often forming large groups with many polyps. They are known from coral reef environments worldwide, and many species have been shown to contain the palytoxin, a lethal toxin named after the genus. It is not known if the two new species contain toxin.

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