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Species spotlight: Egg Yolk Jellies

One of my outreach activities is a guessing game using two sheets of beautiful jellyfish photos my lab mate and I put together. Participants are asked to guess the hilarious common names associated with each species, like pink meanies, snotties, sea tomatoes, and blue blubbers. Of all the species, most folks can immediately guess the Egg-yolk Jellyfish, Phacellophora camtschatica.

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Like a fried egg swimming in the sea….

P. camtschatica are true jellyfish (Class Scyphozoa, Family Phacellophoridae), the only species within the genus and family (Straehler-Pohl et al 2001). They are often confused with the Lion’s Mane’s jellies (Family Cyaneidae) because of similar coloring and size. One distinct difference is the number of lobes, or flaps along the developing ephyrae and medusae; Egg-yolks have 16 lobes that develop into 16 clusters of tentacles, compared to 8 in Lion’s Mane jellies. Egg-yolk jellies can be 60 centimeters (~2 feet) in diameter with tentacles 3-6 meters long, which is fairly large for a jellyfish. These are temperate water animals that live from the Gulf of Alaska to Chile on the Eastern Pacific coast, as well as within the Atlantic and Mediterranean. The delightful yolk-like middle of the medusa is gonadal tissue, and though usually it is yellow, the color can change with their diet.

And their diets are rather surreal. P. camtschatica is a “medusivore.” That means these glorious gelatinous animals survive by eating other gelatinous animals.  Check out this amazing video of P. camtschatica consuming moon jellies from BBC Planet Earth (start at 2:04).

This specialized diet may begin as early as when the ephyrae are released; one study reported that newly liberated ephyrae of Egg-yolk jellies consumed the newly liberated ephyrae of moon jellies, Aurelia labiata (Widmer 2006). Once the medusa develops, Egg-yolks become ambush predators, spending most of their time moving vertically in the water column, often motionless for long periods of time. They move up and down in the water column and snag jellies that are moving horizontally with the current.

Perhaps unsurprisingly given their specialized diet, Egg-yolks host symbiotic amphipods within their bell (subumbrella) and juvenile crabs on the outside of their bell (exumbrella). Even juvenile fishes can live within their tentacles.  We still do not understand how these animals avoid getting stung, or what kinds of defenses they may have against the sticky tentacles that so easily pick off other jellies. A study by Towanda and Thuesen (2006) found up to 326 individual crustaceans, Cancer gracilus, or 446 amphipods, Hyperia medusarum, living on a single medusa! Even more fascinating, larval C. gracilus and H. medusarum feed directly off the medusa (parasitism much?), but C. gracilus larvae become cleaning symbionts as they grow and eventually begin to consume the more problematic, host-consuming H. medusarum. Strange as this mini ecosystem aboard a jellyfish may be, these symbionts are not exclusive to Egg-yolks. C. gracile and and friends have been observed riding several different species of jellyfish medusa, so Towanda and Thuesen (2006) wanted to determine if these animals will ride any gelatinous object. So they built a “pseudomedusa” from gelatin and nylon, then released C. gracilis larvae to see if they would cling on. And they did! I love science.

From a venom perspective, these animals are not wholly impressive. Though unpleasant, their sting is not truly dangerous to humans, which makes some inherent sense. These animals have evolved to attack and consume other gelatinous animals, not vertebrates. I would not be surprised if their venom has specialized toxins for digesting their gelatinous prey. Perhaps that is how these chitin-containing crustacean symbionts and juvenile fish have been able to survive with these animals; the venom is not effective for capturing and consuming them. I can also be assumed these other animals may be slightly faster as escaping than other jellies, and therefore just run away if a host jellyfish become too touchy. It is interesting to think how being a large, slow-moving ambush predator could be directly affecting their venom composition in general, since venoms are assumed to be metabolically costly to make (and likely even more so for a large jellyfish). As of now, their venom have not been characterized.

These are certainly one of my favorite animals to talk about in outreach, but I think they are also some of the most beautiful to watch. I leave you with this soothing video of Egg-yolks.

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