by Mike Ford, Oceanographer, NOAA Fisheries
June 25, 2019
During Dive 05 of the Windows to the Deep 2019 expedition, we encountered a charismatic swimming jelly called a helmet jelly that was twisting and tumbling as it moved across remotely operated vehicle Deep Discoverer’s field of view. With a characteristic groove encircling its swimming bell, the helmet jelly is classified as a coronate scyphomedusa, with the scientific name of Periphylla periphylla. P. periphylla sits in the same class as some common coastal jellies such as the sea nettle, moon jelly, and lion’s mane jellyfish. Our observations were made at nearly 860 meters (2,820 feet) below the waves off the east coast of the United States, but P. periphylla has been observed by oceanographers and explorers working in all of Earth’s ocean basins and has made a big impression on citizens in some coastal communities.
Jellies like P. periphylla seem to swim with a particularly addictive grace – a curiously effective, rhythmic pulsation. Perhaps it is the contraction of the bell closely followed by the movement of a ring of tentacles that makes for such a wonderfully symmetrical display. Maybe it is the flaps that we can see moving back and forth along the bottom edge of the bell. These are called lappets and may have influenced the naming of the species “periphylla” that roughly translates to “leaves all around.” Marginal lappets like these are a characteristic of this grouping of jellies first described in 1809.
It’s hard to miss that very deep red coloration of the stomach. Pigments called porphyrins are responsible for this, and as with many deep-ocean jellies, coloration like this helps the jelly with stealth in the deep-ocean environment, most likely by hiding any luminescent prey in its stomach. The coloration in this specimen seems to be limited to the stomach, suggesting this is a smaller, younger jelly, as the color will begin to spread to the rest of the body as the jelly ages. P. periphylla is particularly bioluminescent, like many related jellies pulsing away in the deep. Light-emitting cells in P. periphylla may be a part of its defense strategy, sending a bright warning when it is touched.
Curiously, with all of this manipulation of light, P. periphylla seems to love the dark. In Norwegian fjords, they are reported to move into the shallow water only at night, and research has shown that light can degrade their valuable pigments.
This article was influenced and inspired by the research and writings of Mike Ford, Frederick Russell, Steve Haddock, Ulf Båmstedt, and Per Flood.