how ancient sea creatures escape death by merging into a single something
Not just ancient, but very ancient
Ctenophores, or Ctenophorais a class of marine invertebrate animals, which has about 100 species. They can be confused with jellyfish due to their external similarity, but they have nothing in common. These ancient inhabitants of the oceans and seas separated from the common tree of life about 100–200 million years earlier than jellyfish, hydra and other coelenterates. That is, they are not just ancient, but very ancient.
Representatives of Ctenophora move in water using cilia, or coelia, located along the body and forming ridges. This is where their name comes from – ctenophores. The coeliums move in a coordinated manner, creating wave-like movements and allowing the animals to move. It is the cilia of animals that create light effects. In jellyfish, the mechanism of movement is based on a different principle: they contract their body, throwing water out of the cavity, and thus create traction.
One of the most impressive abilities of ctenophores is bioluminescence: they can glow in the dark due to special photocytic cells. It is especially well developed in deep-sea species – this is how ctenophores scare away predators and at the same time attract prey.
Some species of ctenophores live in the surface layers of water, but observing and studying them is not an easy task. Invertebrates are so fragile that they get injured when trying to catch them. Few manage to survive after this.
The mission is to escape death
Biologist Kei Jokura, who worked with ctenophores at the Woods Hole Marine Biology Laboratory, noticed an unusual individual among his protégés from the aquarium. It stood out for its size: the comb jelly was twice the size of ordinary ones. And upon closer examination, it turned out that he has two digestive systems.
It has long been known that these jelly-like creatures have the ability to regenerate. But in this case, the restoration process apparently took an unusual path: one ctenophore fused with its fellow – and the result was sea Siamese twins.
The scientist and his team decided to check whether this phenomenon is unique or whether fusion is a normal process for these organisms. Jokura and his team selected 10 pairs of healthy-looking ctenophores, performed several operations (cutting off part of the blade from each individual) and placed them close to each other.
“We left the individuals a minimum of space to move, so there was a small gap between them. Gradually, we watched as this gap closed, and eventually the individuals came into contact with each other.”— commented Jokura.
First, the membranes and epidermal parts merged. Then it was the turn of the nervous system. “The nerves connected, muscle contractions began to synchronize. After 30 minutes the synchronization reached 50 percent, and after two hours they were completely unified,” explained head of the research group. The response to mechanical stimulation of one blade caused a contraction of the entire body, which had become common. This allowed scientists to conclude that the nervous systems had completely merged.
The digestive organs were also united: feeding through one mouth led to the distribution of food into both systems. Despite this, control over excretory processes remained independent: waste products were excreted through two channels at different times.
Of the 10 couples who participated in the experiment, nine merged and survived. The researchers suggested that ctenophores do not have an allo-recognition mechanism, that is, they are not able to distinguish their own cells from others. Now the next step is to find out whether individuals of different species can grow together.
Similar merger cases
The experiments were conducted with a ctenophore known as the sea walnut (Mnemiopsis leidyi). Similar merger observed in another species of ctenophores, the Black Sea pleurobrachia. In this case, the unification occurred without complete integration: the reactions of the two pleurobrachia remained uncoordinated, and each partially retained its independence. Perhaps the ability to completely merge is not inherent in all species of ctenophores.
Other marine organisms, e.g. salpsare able to “merge” into colonies of tens and hundreds of “units”. But this process differs from the unification of ctenophores into a single whole: the salps in the colony remain autonomously functioning individuals within the framework of the natural reproduction cycle.
The study of ctenophores opens a new chapter in biology and could have far-reaching implications for regenerative medicine. Biologists are already exploring the possibility of using these mechanisms to create bioimplants and artificial organs. But for now this is only the beginning of a long journey.
