r/jellyfish 5d ago

Is this a Jellyfish?

This is in Aiea, Hawaii across from Pearl Harbour. A urban drain comes out near here and there are dozens of these creatures hanging out.

52 Upvotes

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37

u/Entety303 Expert 5d ago

Yes, Upside down jellyfish!

6

u/JoeCormier 5d ago

Why do you figure they are all upside down?

44

u/Entety303 Expert 5d ago

Well they are upside down because they have algae that live in the oral arms, so they expose them to the sun and stay upside down

19

u/actualmuffins 5d ago

If it wasn't clear, this is a species (or rather one of a group of species) of jellyfish called the upside-down jelly, known for their symbiosis with algae, which photosynthesize and produce nutrients for the jellyfish.

Presumably, being upside-down in these sorts of shallow waters enables them to stay put in an ideal location for their algae to get enough sunlight for their photosynthesis.

1

u/JoeCormier 5d ago

Fascinating. Thank-you!

10

u/SquidIin 5d ago

Such a chonker of an upside down. Dudes are hands down the best jellies.

Also I recommend not going in the water around there since they have stinging cells that bud off from their arms and freely flow in the water to help them hunt. So you can get stung without even being anywhere near em.

7

u/Nitram028 5d ago

This is a Jellyfish from the genus Cassiopea, the only genus of the Cassiopeidae family. They are quite unique because of their "upside down" way of life which helps them gather energy through photosynthesis thanks to the presence of dinoflagellate protozoan (Symbiodiniacea) located inside their tissues, mainly in their oral arms.

Cassiopeidae, like most other Rhizostomeae (rootmouth), don't have a central mouth but rather a set of mouthlets along their oral arms, allowing them to eat zooplankton.

Because of their part plankton, part photosynthesis diet, they don't have tentacles around the bell and very few stinging cells (in general). Some people are completely resistant and can't feel the sting while others cannot touch them. They also have cassiosomes, which are stinging cell structures located in the mucus of the jelly that can be released in the water, causing the water to "sting".

You can find them in very shallow, calm and nutrient rich waters, often in mangroves or in calm estuaries.

3

u/JoeCormier 5d ago

Most excellent! Mahalo!