Tokyo Sea Life Park 's "Tokyo Sea" area has been exhibiting glass jellyfish since October 16, 2014 (photo above).

The glass jellyfish is distributed north of the Kanto region and is commonly seen from winter to spring. When fully grown, its bell reaches a diameter of about 5 centimeters, and it has about 32 long tentacles. The name "Giyaman" refers to glass products or glasswork, and is derived from the Dutch word "diamant" (meaning diamond). As its name suggests, it is a transparent and very beautiful jellyfish.

The specimens on display this time are offspring that bred from individuals collected in Tateyama Bay in June. About two weeks after collection, we noticed thread-like structures attached to the walls and glass of the tank where they were being kept (see photo below). These are called polyps, which are the anemone-like structures that hatch from eggs and are connected at the base. The polyps continue to multiply by repeatedly dividing and budding (new polyps identical to themselves are formed from the base), and they spread all over the tank.

About two weeks later, we discovered tiny jellyfish, about 1 millimeter in diameter, swimming in the tank. Upon closer inspection of the polyps, we saw that "jellyfish buds," the precursors to jellyfish, were forming at the base of the anemone-like structure, and many jellyfish that looked ready to swim away were attached to them. Subsequently, jellyfish began to swim out of the polyps one after another, and so far, more than 1,000 offspring have been born from the five parent individuals.

The long tentacles, a characteristic feature of the glass jellyfish, are very short when they are born and gradually grow longer as they mature. The long tentacles easily get tangled, and if the water current is too strong, they tangle even more; if it's too weak, they sink. Adjusting the water current to just the right strength was quite a challenge. Seeing them fully grown with their long tentacles, I was reminded of what a beautiful jellyfish they are.

We will do our best to keep the exhibit on display for as long as possible so that many people can see the beautiful appearance of the glass jellyfish.

Photo above: The glass jellyfish, which went on display on October 16, 2014.
Photo below: Polyps of a glass jellyfish

[Mayuko Muramatsu, Animal Care and Exhibition Staff, Tokyo Sea Life Park]