2023-06-02 20:01:02
They often look like a transparent gooseberry with a number of wispy whiplashes. Comb jellyfish they are called in Dutch, in English they become comb-jellies called, or comb jellyfish. Ctenophora is the scientific name, which literally means comb-bearer, from the Greek words kteis (comb) and forein (wear).
That ‘comb’ refers to rows of whip hairs with which the transparent creatures move. So much for the etymology, it’s about the animals themselves. It has recently been published that these turn out to be at the basis of all other multicellular animal life forms.
Originally all terrestrial life was unicellular, from the very beginning about 3.8 billion years ago to 700 million years ago. Then the first multicellular life forms emerged. Soon the first split occurred in the family tree of the animals. One branch led to the comb jellies, the other to all the other animals we know today, from badger to centipede and from jellyfish to cockatoo.
One step up the evolutionary ladder
The research that came to this startling conclusion made it to the weekly Nature. With that, the comb jellies have won an evolutionary debate, namely whether comb jellies or sponges are the oldest sister group of all other animals. To summarize a long and complicated story, there are genetic similarities between comb jellies and single-celled animals on the one hand, and between sponges and the rest on the other.
Sponges were (and are) usually regarded as the most primitive of animals because they lack organs such as muscles, an intestinal tract and nerves; they seem more like a colony of well-cooperating unicellular organisms than a true multicellular organism. Now, together with the other animals, they appear to be one step higher on the evolutionary ladder than the comb jellies.
The conclusion that comb jellies dangle at the very bottom of the family tree is so counterintuitive that the researchers who published this initially felt ‘as if they were banging their heads against a wall’. The fact that sponges don’t have true organs, and comb jellies as well as the other animals do, makes the conclusion interesting. Have the sponges lost their organs again?
Comb jellyfish in an Amsterdam canal
The new research places the hallucinatory-looking comb jellies on a special pedestal. There are only about one hundred and fifty species of Ctenophora worldwide. Most are small, growing no more than a few centimeters, although there is one ribbon-shaped species that can reach five feet in length.
There are several types of comb jellies in the Netherlands; the sea grape Pleurobrachia pileusthe also indigenous Infundibulum bolinopsis (which as far as I can tell has no Dutch name and which occurs in the cooler waters of the North Sea), the large melon jellyfish Beroe cucumbersthe slender melon jellyfish Beroe slender and the invasive American comb jelly Mnemiopsis leidyi.
The latter species probably ended up here with ballast water and sometimes occurs in extremely large quantities in the Wadden Sea, the Oosterschelde and the Grevelingen. They are tolerant of brackish water; American comb jellies have even been found in an Amsterdam canal. Fortunately, they are eagerly eaten by both melon jellyfish. You should get it from your family.
Jelle Reumer is a paleontologist. Every week he discusses an animal that makes the news for Trouw.
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