This animal has a swimming medusa and a minute mud-dwelling polyp. DNA research connected forms that had been treated as separate species.
The medusa has four short, knob-tipped tentacles. The polyp is spindle- or club-shaped, with short tentacles below the mouth.
Off Northeast Greenland, the swimming medusae of Plotocnide borealis are especially associated with colder waters above the continental shelf. They occur at different depths, and their principal depth layers differ between locations.
In August–September 2017, r/v Dana sampled nine stations on northern and southern coast-to-ocean transects. Researchers analysed 32 samples taken with depth-stratified nets and measured water properties. Among eleven gelatinous taxa, borealis contributed the largest share, 34.6% of individuals. It dominated intermediate and deep shelf layers in the north, but shallow and intermediate shelf layers in the south. It was the only gelatinous taxon recorded over the southern shelf.
An extinction-risk assessment has not been added yet.
Potential changes associated with warmer Atlantic water are a conservation concern for Northeast Greenland marine communities. The 2023 study identified borealis as characteristic of colder shelf waters. Its authors call for further shelf surveys and long-term data to help forecast changes in local gelatinous assemblages.