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The distribution of a deep-sea jellyfish species with two different traits hints at the existence of an unknown biogeographic barrier in the North Atlantic Ocean, according to new research by marine scientists at The University of Western Australia.

Dr. Javier Montenegro, from UWA's School of Biological Sciences and the Minderoo-UWA Deep-Sea Research Center, was lead author of the published in Deep Sea Research Part I: Oceanographic Research Papers.

"This jellyfish, the trachymedusan subspecies Botrynema brucei ellinorae, has two different shapes depending on which area it occurs in—one with a distinctive knob at the top and one without," Dr. Montenegro said.

"Both types occur in the Arctic and sub-Arctic regions, but specimens without a knob have never been found south of the North Atlantic Drift region, which extends from the Grand Banks off Newfoundland eastwards to northwestern Europe."

The study used historical observations, photographic records and genetic analyses to examine the distribution of the jellyfish around the world.

Researchers found that genetic data linked the specimens both with and without a knob in the Arctic and sub-Arctic regions to specimens with a knob found in the subtropical western Atlantic region.

"The differences in shape, despite strong genetic similarities across specimens, above and below 47 degrees north hint at the existence of an unknown deep-sea biogeographic barrier in the Atlantic Ocean," Dr. Montenegro said.

The findings suggest that a semi-permeable barrier is located in the North Atlantic Drift region.

"It could keep specimens without a knob confined to the north while allowing the free transit of specimens with a knob further south, with the knob possibly giving a selective advantage against predators outside the Arctic and sub-Arctic regions," Dr. Montenegro said.

"The presence of two specimens with distinctive shapes within a single genetic lineage highlights the need to study more about the biodiversity of gelatinous marine animals."

The potential existence of a semi-permeable biogeographical barrier associated with the North Atlantic Drift has important consequences for understanding patterns of biodiversity, species evolutionary processes and their dispersal across ocean basins.