Unusual solitary marine species discovered

TOKYO: Scientists have discovered a very unusual new marine species of zoantharian, buried almost completely in the soft sediment of a seafloor in Japan.

Researchers from Kagoshima University and University of the Ryukyus in Japan stumbled upon a solitary individual polyp around the southern Japanese island of Okinawa.

They noticed that the creatures were buried almost completely in the soft sediment of the seafloor. It was only their oral disks and tentacles that were protruding above the surface, they said.

Generally, most known zoantharians are colonial (hence their common name of 'colonial anemones'), and many dwell in shallow waters of subtropical and tropical regions, where their large colonies can be found on coral reefs, researchers said.

These newly discovered polyps were not only leading solitary lives. They were also found to lack zooxanthellae, single-celled organisms that coexist in symbiosis with certain marine invertebrates, also typical for the majority of zoantharians, they said.

Solitary zoantharian species, such as this one, are known from scant few reports, and only three species are described, all reported more than 100 years ago from the Indo-Pacific region. Overall, very little is known about the hereby studied genus Sphenopus.

The new species, named Sphenopus exilis, is much smaller than the other three Sphenopus species, with its polyps measuring approximately 3 centimetres in length. It is currently only known from two bays on the east coast of Okinawa Island, researchers said.

Both of the bays where Sphenopus exilis is found are threatened by development, with one of the bays currently the centre of controversy over a proposed American military base expansion and landfill, they said.

"This report demonstrates how much more research is needed on these understudied ecosystems," said Takuma Fujii from Kagoshima University.

The findings were published in the journal ZooKeys.