Kurage Wonder Research Club Member's Observation Log / Jellyfish Edition

Kurage Wonder was established in 2020. Here you can encounter around 30 different types of jellyfish.
Jellyfish have a wide variety of characteristics. By learning about the highlights of each species, you may be able to find your favorite jellyfish.

It's spring! It's jellyfish time!

Kyoto Aquarium primarily exhibits jellyfish bred by the "Kyoto Jellyfish Research Department," but sometimes brings back rare jellyfish found in the ocean for display. Especially in spring, when the water temperature begins to rise, many jellyfish start to appear in the ocean.
One thing I secretly look forward to seeing every year around this time is the "Kamikurage" jellyfish.

The Japanese jellyfish (Kamikurage) is a species endemic to Japan that appears along the coasts of Tohoku and Kyushu in the spring, and is also known as the "jellyfish that heralds spring." Among our animal care staff, it's a highly anticipated jellyfish, and we get excited during our spring collecting trips wondering, "Will we find any Kamikurage?"

▶Floating jellyfish

Is the "Kami" in "Kamikurage" (a type of jellyfish) referring to a god? Paper? Hair? Biting?

What is the origin of the name "kamikurage" (divine jellyfish)? When I first saw a kamikurage, I thought, "Ah, I see. It's called a 'divine jellyfish' because it looks so divine." But unfortunately, I was wrong.

From the edge of the bell of the Kamikurage jellyfish, long, fluffy, hair-like tentacles extend, swaying as they drift through the water. That's right! The "Kami" in Kamikurage comes from the word for "hair." Compared to the similarly shaped Jubilee jellyfish and Salsia jellyfish, you can see that it has many more tentacles. (Jubilee jellyfish and Salsia jellyfish have four tentacles.)

At the base of the tentacles are numerous small red dots. These are organs called eyespots, which serve as a substitute for eyes for jellyfish. They can sense light and are useful for determining day and night, and for moving towards brighter areas where plankton gather. However, the eyespots of the jellyfish *Crocothemis servilia* are remarkably numerous and densely packed. To give examples from other jellyfish, the Moon jelly has eight eyespots, and the *Sarsia jellyfish* has four, both distributed at equal intervals along the edge of their bell.

Why can we only meet by the spring sea?

The jellyfish is both familiar and somewhat distant to us jellyfish animal care staff. This is because we can only encounter them in the spring and in the ocean. Many people know that many aquariums in Japan are now working on jellyfish breeding, but even with the technology of Japan, a country with a large aquarium industry, their breeding methods remain a mystery.

Many jellyfish fertilize outside their bodies and then settle on the seabed as small, anemone-like structures called "polyps." It is thought that the jellyfish *Crocothemis servilia* is no exception, but even if fertilized eggs are collected, it seems that it is quite difficult for them to metamorphose into polyps.

At the Kyoto Aquarium, they try to collect eggs and acquire polyps in the years they are able to collect jellyfish, but so far they have not been successful. It's difficult to breed them by human hands, yet jellyfish appear reliably in the ocean every year, which makes me realize just how great and mysterious the ocean is.

By the way, do you know where on the body the jellyfish produces its eggs?
If you hold the transparent umbrella up to the light, you can see a spiraling, swirling organ.

This is the gonad of the jellyfish, where eggs are produced when it matures.
Immature, young jellyfish lack this spiral, and it's fun to observe how they develop a coiled spiral as they grow into adults.

Mature gonads of the jellyfish

Immature gonads

The jellyfish is very mysterious, but my favorite thing about it is the playful side it shows during feeding time. The way it skillfully moves the mouth that extends from the center of its bell and gathers plankton that it has caught with its tentacles reminds me of an elephant using its long trunk to search for food.

▶ Jellyfish munching on their food

The jellyfish is currently on display at the Kyoto Jellyfish Research Club. Depending on the animals's condition, the display may end earlier than planned, so if you're interested, please come and see it soon!

Check out our other jellyfish columns and creature introductions !