Everyone has heard of animals that can lose and then regain a tail or limb. But scientists have discovered two species of Sacoglossana sea slugs that can work even better by discarding and then regenerating a completely new body with a heart and other internal organs.
The researchers also speculate that slugs may use the photosynthetic ability of chloroplasts, which they get from algae into their diet, to survive long enough to regenerate.
“We were surprised to see the movement of the head immediately after the autotomy. We thought that the slug would soon die without a heart and other important organs, but we were again surprised to find that it regenerates the entire body. “Sayaka Mito of Nara University in Japan
This discovery was pure coincidence. In the laboratory of the university, sea slugs are grown from eggs to study the features of their life cycle. One day, scientists saw something unexpected: Sakoglossan moved without its body. They even witnessed one slug doing it twice.
The researchers report that the head, separated from the heart and body, moved on its own immediately after separation. After a few days, the wound closed. The heads of relatively young slugs began to feed on algae in a matter of hours. Within a week, they began to regenerate the heart. After about three weeks, the regeneration was completed.
The heads of the elderly individuals did not eat and died after about 10 days. In any case, the outcast bodies did not rebuild a new head. But the heads did move and respond to touch for days or even months.
Scientists don’t know how sea slugs do it. But they suspect there must be stem cells at the severed end of the neck that can regenerate the body. It is also unclear why they do it. One theory is that it helps to remove internal parasites that prevent them from reproducing. They also don’t know what immediate signal prompts them to throw off the rest of their body.
The sea slugs in question were already unique in that they take chloroplasts from the algae they eat into their own body – a habit known as kleptoplasty. This gives the animals the ability to feed their bodies through photosynthesis. They speculate that this ability may help them survive after an autotomy (dropping off a part of the body) long enough for the body to regenerate.
These findings in sea slugs represent a new type of autotomy in which animals with complex body structures lose most of their body.