Comb jellies safe to swim with and to handle
Published 30/07/2016 | 00:00
I heard there was a wreck of comb jellies on the strand and while I didn't go down immediately to see these delicate, transparent jellyfish I did keep them in mind. The next time I was on the shore I was pleased to see that they were there again in their thousands along the tideline.
Comb jellies are a tiny group of creatures that comprise a phylum all on their own. In the classification of the animal kingdom, a phylum is the uppermost division of the kingdom. For example, all of the tens of thousands of back-boned animals - fish, amphibians, reptiles, birds and mammals-make up one phylum. Only a handful of species of comb jellies are known but they are so unique they are assigned to a phylum of their own, Phylum Ctenophora.
Five species have been recorded in European waters. Only one, the Sea Gooseberry, has a common English name. It is widespread and common around Ireland. It is about the size and shape of a gooseberry but is transparent so, on the beach, it looks like a shining blob of wallpaper paste. It comfortably fits on a teaspoon.
Closer examination of the gooseberry-like, rigid blob of jelly reveals that the creature's transparent body is ribbed. The ribs are eight in number and run along the length of the body. Along each rib there is a comb-like structure with rows of tiny hairs that the animal beats to enable it to swim.
It is the possession of these combs that make these jellyfish unique resulting in them being assigned to a group all on their own. However, their little swimming combs are not powerful enough to enable them to swim against currents and tides so rafts of them regularly get wrecked on beaches.
All comb jellies are meat-eaters. They swim in surface waters using sticky tentacles to catch tiny creatures in the soup of plankton that the sea supports.
Most comb jelly individuals are both male and female. They can produce both eggs and sperm, can fertilise themselves and can therefore produce young without the need for a partner. As a result, the population can multiply rapidly when conditions are right.
In high summer, comb jellies often swarm inshore. They spawn at night when the water is particularly warm. In the dark, they are phosphorescent and light up the sea with a dull eerie glow.
Unlike other jellyfish, comb jellies do not sting people so they are safe to swim with and to handle.