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A guide to aquatic creatures you'll want to encounter at the aquarium: Jellyfish

Jellyfish, of which there are said to be thousands of species worldwide, are made up of over 90% water. They are a type of plankton that are weak swimmers and are broadly divided into two phyla: the poisonous Cnidaria and the non-poisonous Ctenophora, which have shiny comb plates. We introduce some unique jellyfish that you'll want to encounter at the aquarium.

Photo: Satoshi Nagare, Tsuruoka City Kamo Aquarium / Text: Masae Wako

Aquatic Creatures Encyclopedia -Jellyfish Edition-
moon jellyfish
Glass jellyfish
Cannonball Jelly
Keynote jellyfish
Flower jellyfish
melon jellyfish
Rhino jellyfish
Spiny jellyfish
Palmo
Lycopersicon gracilis
Horseshoe jellyfish
Aequorea victoria
Atlantic Sea Nettle

moon jellyfish

Jellyfish-like jellyfish found in oceans around the world

moon jellyfish
Cnidaria (Cnidaria jellyfish) are primarily larvae that hatch from eggs and attach to rocks or seaweed to become polyps, which then clone and multiply. Moon jellyfish are produced in large numbers during this process. The four-leaf-like parts on the umbrella are the stomach cavity and reproductive glands.

Glass jellyfish

Transparent as glass, it's actually a new species

Glass jellyfish
Cnidaria. Umbrella diameter: 3-5cm. Appears from winter to spring in areas north of the Kanto region. Has a relatively weak venom. "Giyaman" is a Dutch word meaning glass or diamond. It was first recorded in Japan in 1925 and was thought to be an existing species, but genetic analysis in 2021 revealed it to be a new species.

Cannonball Jelly

It has a bullet-like shape and swims straight and fast.

Cannonball Jelly
Cnidaria. An overseas species that lives off the coast of South America. The umbrella diameter is 7-8cm, with larger specimens reaching over 20cm. The oral arms that carry food to the mouth are short and extend outwards, and are used to catch prey. The Tsuruoka City Kamo Aquarium is exhibiting an individual bred from overseas polyps for the first time in Japan.

Keynote jellyfish

The terrifying bandage bug stings with a venom that causes agony

Keynote jellyfish
Cnidaria. Found along the coast of Japan. They live by attaching themselves to seaweed and prey on crustaceans and young fish with the tips of their hook-shaped tentacles. Although they are small, with a cap diameter of 1-2cm, they pack a powerful venom. In Yamagata Prefecture, they are feared and known as the "bandemushi" (a term so painful it can upset a rice cooker).

Flower jellyfish

Vivid, swaying nocturnal creatures

Flower jellyfish
Cnidaria. Appears in the spring off the coast of Honshu. Cap diameter 5-10cm. Nocturnal and highly venomous. Characterized by an appearance resembling the hats worn in the Hanagasa Festival, it has vibrantly colored tentacles. Its favorite food is small fish and it will not accept any other food. In 2017, a new green fluorescent protein was developed from the tentacles.

melon jellyfish

Ctentacleless comb jellies swallow their prey whole!

melon jellyfish
Ctenophora - comb jellies swim by moving the comb plates that cover their bodies in small movements. As they do so, the comb plates reflect light and shine. The gourd-shaped comb jellyfish can be found throughout Japan, and is 5-15cm in length. Although it has no tentacles, it is a fierce creature that can swallow comb jellies that are larger than itself whole.

Rhino jellyfish

The ultimate edible jellyfish with a round, thick cap

Rhino jellyfish
It is a member of the Cnidaria phylum. Its umbrella diameter is large, measuring 30-50cm. It is also one of the most edible jellyfish, and lives in the waters off the coast of Japan. There is a record of cooking "Bizen Province jellyfish" on a wooden tablet dating back to the Nara period. The thick umbrella is also used as a hiding place by horse mackerel and stonefish.

Spiny jellyfish

Swimming towards the light, bouncing

Spiny jellyfish
Cnidaria. Inhabits the seas south of Honshu. The umbrella diameter is about 6 cm. The long tentacles extending from the bell-shaped umbrella resemble hair. There are hundreds of light-sensitive red eyespots on the edge of the umbrella, and it swims towards the light. It is difficult to transform the eggs into polyps, so there have been no successful breeding cases.

Palmo

Large white umbrella with violet trim

Palmo
Cnidaria. An overseas species found in southern Europe. The cap diameter is 60-90cm. The edges become colored as it grows. Kamo Aquarium, Tsuruoka City, successfully bred this species using polyps donated by the Vienna Zoo, and in 2018 it was exhibited for the first time in Japan. Its English name is Barrel Jellyfish.

Lycopersicon gracilis

A comb jelly that lives on the ocean floor. Its name comes from the lyre.

Lycopersicon gracilis
Ctenophora. Body length is 10-20cm. It was discovered by Emperor Showa off the coast of Sagami Bay in 1941. It lives attached to rocks on the ocean floor at depths of 80m or more, extending its comb-like tentacles to feed on zooplankton. It comes in a variety of colors, including yellow, orange, and white with red polka dots.

Horseshoe jellyfish

Like a transparent helmet decorated with illuminations

Horseshoe jellyfish
This species is part of the phylum Ctenophora and is commonly found throughout Japan. It is 5-10cm long. Its surface is covered with eight rows of comb plates, each made up of tens of thousands of cilia, which reflect light and give off an iridescent glow. It spreads its sleeve-like projections on both sides and preys on plankton and small crustaceans with its sticky cells.

Aequorea victoria

The bowl-shaped luminous jellyfish that led to a Nobel Prize

Aequorea victoria
Cnidaria. Found throughout Japan. Cap diameter is 5-20cm. When stimulated, the edge of the cap glows green. The photo shows the overseas species Victoria. The late Dr. Osamu Shimomura and his colleagues discovered the green fluorescent protein in the cap edge of this species, and were awarded the Nobel Prize in Chemistry in 2008.

Atlantic Sea Nettle

A highly poisonous jellyfish with frilly mouth arms

Atlantic Sea Nettle
Cnidaria. An overseas species. Found on the east coast of the United States. Its cap diameter is about 20cm and it has 40 tentacles. Its transparent cap and oral arms are elegant, but the name "sea nettle" means "sea nettle." Its poison is highly potent. A similar species is the Atlantic bay nettle, which has 24 tentacles.

©Tsuruoka City Kamo Aquarium

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