Jellyfish are now sea jellies

Photo credit: Hodgers

Starfish are now known as sea stars and jellyfish are now known as sea jellies. Sometimes jellyfish are referred to as just jellies, but I prefer sea jellies, this name better orients the mind.

Why the switch? Jellyfish aren’t fish, making the name sea jellies more accurate, but the new term is having a tougher time catching on compared to sea star. So for the purposes of this blog I will be using both names to avoid confusion and also help people transition.

Sea jellies are members of the phylum Cnidaria (the C is silent) and also members of the subphylum Medusozoa. Their bodies are made up of mesoglea, a jelly-like material. According to a “jellyfish has two layers of skin – epidermis or the outer layer and gastrodermis or the gut lining. A layer of thick gelatinous substance called mesoglea fills the portion between these two skin layers.” Mesoglea gives sea jellies much of their substance, which isn’t much considering they are 95% water.

Mesoglea is another great science name that actually makes sense. explains that meso is Greek for middle and glea derives from the ancient Greek work gloia meaning glue. And that’s exactly what mesoglea is, the glue holding together a sea jelly’s middle layer.


  1. JNapoli says

    I don’t know if I’m willing to make the switch….a lifetime of calling them jellyfish! But I would never have known there was a site called if I hadn’t read this, so the day has meaning. And jellies have no brains! (The dumb mobster in “Analyze This” was named Jelly. Go figure.)

  2. steve says

    I remember this back when I took an oceanography class in high school. The teacher kept refering to jellyfish as sea jellies. I stopped her and asked why she called them this. She said they are not technically fish so sea jelly is more appropriate. I said in response well they aren’t technically jelly either. The class began to chuckle and I was in trouble.

    This was back in the day before I learned to shut my mouth…

    • Carolyn Kraft says

      Steve, I think you made an excellent point. Too bad teachers don’t always appreciate a good sense of humor!

    • Pete says

      Adding the word fish implies gills. Jellies do not have gills. You are right, they are not jelly, but do look like jelly in the water but they definitely do not look like fish and they’re not.

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