The Question: We found clear jelly like blobs washed up along the ocean beach. They look like they could be jellyfish without tentacles. I stepped on one by mistake and it did not hurt. What are these?

Submitted by: Sheri, Rhode Island, USA

(click on photos and graphics to expand)

Aurelia labiata

Aurelia labiata

The Short Answer: Sheri, what you are describing sounds like the remains of jellyfish, probably moon jellies (this includes several species in the genus Aurelia).  (see this post for a different possibility) People report seeing these jelly discs on beaches all over the world. David Albert, professor emeritus at the University of British Columbia, has studied Aurelia labiata, the moon jelly that is common on the west coast of North America (Aurelia aurita is the east coast version). He says that what you are seeing is the “mesoglea” of the jellyfish.

moon jelly anatomy

(1) stomach (2) tentacles (3) oral arm (4) mesoglea (5) gonads (6) endoderm (7) mouth

The mesoglea is a stiffer layer of jelly that provides structure to the moon jelly. So when you find one on the beach, you are essentially finding the skeletal remains of a dead jellyfish.

Live moon jellies don’t generally cause a sting that you would notice, and once they die, the hundreds of tiny tentacles fall away pretty quickly, so as you discovered, you don’t have much to worry about in picking up a moon jelly disk. That is not true of all dead jellyfish, however, so you should be a little cautious.

I wrote previously about moon jellyfish at


Stranded moon jelly

How do They Get on the Beach?:
A moon jelly doesn’t want to be on the beach, of course. But although they can swim by pulsing their bell to push themselves through the water, they’re not exactly strong swimmers. By angling in one direction or another, they get some directional control, but for the most part, they can swim up and float down. So it seems like it might be pretty easy for a moon jelly to end up on the sand, doomed to disintegrate and be picked up by beach goers. It turns out, however, that moon jellies have behaviors that almost always keep them off the beach.

Dr. Albert has studied the behavior of moon jellies and has found that while they normally keep themselves a meter or two (about six feet) away from the surface of the water, if they bump into or sense the bottom in shallow water, they swim up and stay near the surface for some period of time. Why would they do that?

When waves break in shallow water and then recede, the overall flow of water is shoreward at the bottom and seaward at the surface. That seaward flow at the surface is called an ebb flow. When moon jellies reverse their normal behavior in shallow water to position themselves near the surface, they place themselves in that ebb flow and get carried out into deeper water.


This doesn’t always work, of course. Dr. Albert says, “Moon jellies have behaviours that help them avoid stranding. However, jellies are primitive animals. Their behaviour has to be looked at statistically. The behaviours don’t always occur at the optimum time . For example, in some jellies, swimming toward the surface doesn’t occur until the water has become quite shallow. In that case, the ebb stream may no longer be very strong and it may be very thin. So, a jelly may be less likely to drift out of a shallow area and less likley to avoid stranding. Also, if there is a wind pushing them toward a shore on an ebb tide, they may become stranded.   The ebb tide will serve to help them drift away from the beaches, but the wind initiated currents may be stronger.”

Still, despite these occasions when the normal behavior doesn’t work, Dr. Albert asserts that the vast majority of moon jellies don’t become stranded. He says the ones that end up as mesoglea disks on the sand were probably dead before they washed ashore.

A Little Jellyfish Anatomy: What looks like a simple blob of jelly is actually a fairly complex blob of jelly. Surrounding the mesoglea disk are layers of tissue that contain channels to move tiny particles of food from the edge of the jellyfish bell to the center, where its mouth and stomach are. When you see a live moon jelly, you’ll also notice four prominent horseshoe-shaped objects. These are the moon jelly’s gonads, where it produces eggs or sperm. When you find a dead moon jelly on the beach, you may see a blob that is 25-40 cm (10-16 in.) wide, and includes the four horseshoe shaped gonads. That would represent a fairly intact adult moon jelly. As it becomes more and more degraded by wave action and decay, all that’s left is the tougher center of the mesoglea disk, which might be as little as 7 cm (2.5 in.).

What Does a Jellyfish Think About: Dr. Albert is a behavioral neuroscientist, so his interest in moon jellies isn’t really in how they end up on beaches. He is fascinated by the fact that a moon jelly can exhibit true behaviors, even though it has a nervous system that doesn’t look anything like what we think of as a brain. There is no central mass of nervous tissue in the head of a moon jelly. A moon jelly doesn’t even have a head. It’s “brain” is spread throughout the organism. Yet it changes its swimming behavior and direction in response to complex sensory information that includes temperature, salinity, touch, and light levels. Somehow, without having what we think of as a brain, it coordinates this information from the various parts of its body and “decides” on a response.

These are not simple reflexes, like when your hand jerks back in response to heat. This is more like you lying in the hot sun and deciding, “I’m getting hot, I should go be in the shade.”

No one is suggesting that a moon jelly “thinks” the way we do. But it seems to take in sensory data and then change its behavior over a period of time, which suggests some kind of processing. Jellyfish have been around for about 500 million years. Far longer than us and even longer than dinosaurs. In fact, if longevity is the measure, then jellyfish are one of nature’s big success. Dr. Albert’s hope is that by studying the simple behaviors of an animal that was “thinking” long before we were, we can gain insight into how all animal brains work.

moon jellies

Aurelia aurita

Jelly and Peanut Butter: If you search online for “moon jellies on a beach,” you’ll find other sites that show pictures and if you look at the comments, you’ll see numerous jokes about jellyfish washing ashore in their desperation to find peanut butter. On one of the sites I came across, someone called OceanDreamer went one step further:

“My intuition tells me that thousands of jelly fish came ashore searching for peanut butter fish. They combine for a tasty treat because of the sand-which-is there.”

I should probably turn off the comments on this article to avoid jelly and peanut butter jokes, but I kind of like them.

Sources: Albert, D J. (2014). Field observations of four aurelia labiata jellyfish behaviours: Swimming down in response to low salinity pre-empted swimming up in response to touch, but animal and plant materials were captured equally. Hydrobiologia, 736(1), 61-72.

Albert, D J. (2011). What. Neuroscience & biobehavioral reviews, 35(3), 474-82.

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