Don’t ever trust a marine biologist when they tell you what their favourite sea creature is, because it’s guaranteed to be something else the next day. Today, my favourite creature is the weird and wonderful comb jellyfish. Depending on which way the wind is blowing, where the currents are going and what the tide is doing, you might find yourself swimming in a sea of them! Luckily they are as harmless as they are beautiful.
Eline, Soneva Fushi’s marine biologist is fascinated by these beautiful creatures (photo by Rob Auger).
Here’s the interesting thing: comb jellyfish aren’t true jellyfish. While they look very similar due to their gelatinous appearance, they are not related at all, and easy to confuse. Comb jellyfish are a bit more complex in the way their digestive system works. When jellyfish eat, they will spit anything out that is undigested. The same opening does double duty. Comb jellyfish will excrete their waste a bit more elegantly: in one end, and out the other. This was an important discovery in understanding gut evolution, because it turns out that they have inherited this design from a common ancestor with… us!
Comb jellies spend most of their time near the surface of the water, and have iridescent bands running along the length of their bodies. If you manage to get a closer look, you can see tiny comb-like plates called cilia that they beat to propel themselves forwards. As they swim, each plate refracts the light, which produces a glittering rainbow effect.
Spreading to dine
As the comb jelly drifts along the currents of the ocean, it spreads out two lobes on either side of its body to catch food. Rather than using stinging cells (cnidoblasts) to capture prey, it uses sticky cells (colloblasts) to make plankton stick to its lobes before it’s swept towards the waiting mouth using fine hairs.
Comb jellyfish spreading out to dine (photo by Lyn Gately).
Did you know?
- Unlike jellyfish, comb jellyfish can’t sting you at all
- It is okay to gently touch them, but don’t take them out of the water
- Overfishing is removing predators of comb jellyfish, meaning some types may find it easier to grow and survive