Fascinating facts and myths about Sea Jellies

Made up of over 90% water, sea jellies (or jellyfish) are living fossils which have existed for at least 500 million years. Amazingly, they have managed to survive till this day with neither a brain nor heart. Instead, these ocean drifters have a ring of nerves called a nerve net, which transmits information about its surroundings throughout their body.

Here are more fascinating facts about these sea creatures:

Largest Sea Jelly: Lion’s Mane Sea Jelly

Image credit: NC ; Image source

The Lion’s Mane Sea Jelly (Cyanea capillata) has a bell that can reach about 2.4 metres in diameter and tentacles that can can grow up to 37 metres long, which is even longer than the length of a blue whale, the largest animal on Earth. The largest Lion’s Mane Sea Jellies are found in Arctic waters. Lion’s Mane Jellyfish

Smallest Sea Jelly: Irukandji Sea Jelly

Image source: Wikipedia

The Irukandji Sea Jelly (Carukia barnesi) may be as small as a pea (1-2cm) but it is also one of the most venomous. It fires its stingers into its victim, causing symptoms collectively known as Irukandji syndrome. Unless immediate medical action is taken, those affected can, in rare instances, go into cardiac arrest and die. Irukandji Jellyfish

Eternally Youthful Sea Jelly:  Immortal Sea Jelly

Image credit: National Geographic

The Immortal Sea Jelly (Turritopsis dohrnii) has the ability to “age” backward from adult stage to an immature polyp stage over and over again. When that happens, its tentacles retract, its body shrink, and it sinks to the ocean floor and starts the cycle all over again. The only known way it can die is if it gets consumed by another fish or if a disease strikes the jelly. However, there are still many mysteries surrounding this marine immortal. Immortal Jellyfish

Deadliest Sea Jelly: Box Sea Jelly

Image source

Considered the most venomous marine animal, the Box Sea Jelly (Chironex fleckeri) is so deadly that it can cause paralysis, cardiac arrest, and even death within 5 minutes of being stung.

It has up to 15 tentacles growing from each corner of its bell and can reach three metres in length. Each tentacle has about 5,000 stinging cells, which are triggered not by touch but by the presence of a chemical on the outer layer of its prey. Its sting is so painful that human victims have been known to go into shock and drown or die of heart failure before even reaching shore. Those who survive experience considerable pain for weeks and often have significant scarring where the tentacles made contact. box jellyfish

Most Influential Sea Jelly: Crystal Sea Jelly

Image credit: Sierra Blakely, image source: Wikipedia

The Crystal Sea Jelly (Aequorea victoria) is perhaps the most influential sea jelly in the field of biomedical science. This bioluminescent sea jelly produces flashes of blue light by a quick release of Calcium++ which interacts with the photoprotein aequorin. The blue light produced is in turn transduced to green by the now famous green fluorescent protein (GFP).

In 1961, Dr Osamu Shimomura and Professor Frank Johnson isolated the fluorescent protein aequorin, and its small molecule cofactor, coelenterazine, from large numbers of Crystal Sea Jellies. They discovered that calcium ions (Ca2+) were required to trigger bioluminescence. This research also marked the beginning of research into GFP which was summarized by Dr Shimomura. For his research into GFP, Dr Shimomura was awarded the 2008 Nobel Prize for chemistry, together with Martin Chalfie and Roger Tsien.

GFP is now widely used as a biological highlighter to track how cancer cells spread, how HIV infections progress and even which male ends up fertilising a female fruit fly’s egg. Crystal Jellyfish

Fluorescent proteins allow us to visualize cellular structures. Here, cell membranes are marked with GFP (green), and cell nuclei with mCherry (red). Image source: The Lunenfeld-Tanenbaum Research Institute

3 myths about sea jellies

MYTH #1: Sea jellies attack humans
False. Sea jellies do not seek out human nor eat us. Instead, they feed on microscopic plants and fish eggs/larvae, or other prey like fish, worms, and crustaceans. Hence any contact with a sea jelly is incidental. But when we are in their environment, we can get in the way of their stinging tentacles.

MYTH #2: We will die if we get stung by sea jellies
Again not true. Depending on the species involved, sting effects can range from mildly irritating to extreme pain to death. For example, Box Sea Jelly stings can be deadly while Moon Sea Jelly stings generally impart a mild stinging sensation and are not usually deadly. Which brings us to the next myth below…

MYTH #3: Applying urine to a sea jelly sting reduces the pain
Perhaps the most interesting of myths which has been proven to be unhelpful. Instead, try rinsing the area with an acidic liquid like vinegar. And never rub the affected area as that will only aggravate the wound.

Here’s a video explaining how Sea Jellies sting:

Come learn more about sea jellies at Glowing Ocean, currently happening at the S.E.A. Aquarium till 6 Jan 2019. Sea jellies and our newly revamped sea jellies habitat are among the highlights of this year-end festive event. Find out more about Glowing Ocean

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