Off With Their Heads! Decapitated Sea Slug Head Regrows Body

Much like a body horror movie plot, sea slugs may chop off their own heads to rid themselves of parasites, find scientists in Japan.

AsianScientist (Mar. 12, 2021) – From salamanders to starfish, animals that regrow lost tails or limbs are nothing new. But in an incredible—if slightly gruesome—twist, scientists from Japan have identified two species of sea slug that can regrow their bodies after decapitating themselves. Their findings were described in Current Biology.

Similar to other great scientific breakthroughs, researchers stumbled upon the wondrous aquatic critter by accident. As with many serendipitous discoveries, the story starts in the laboratory—specifically, Dr. Yoichi Yusa’s at Nara Women’s University, where they study the life history of sea slugs.

One day, PhD candidate Ms. Sayaka Mitoh witnessed a scene seemingly straight out of a horror movie: a disembodied sea slug head crawling around the bottom of the tank. After this startling discovery, Mitoh and her colleagues took a closer look at the sea slug species in question, namely Elysia marginata, as well as another species called E. atroviridis.

Over the course of their study, five out of 15 E. marginata and three of 82 E. atroviridis decapitated themselves—with their heads moving on their own almost immediately after separation. Within days, the neck wounds had closed, with the decapitated heads subsequently feasting upon algae. After a week, regeneration of the heart had begun. And in less than a month, most of the sea slugs had regenerated entirely new bodies, internal organs and all.

“We were surprised to see the head moving just after autotomy (the removal of a body part),” shared Mitoh. “We thought that it would die soon without a heart and other important organs, but we were surprised again to find that it regenerated the whole body.”

While the biological significance behind the sea slugs’ self-decapitation remains unclear, Mitoh and Yusa suspect that parasites may be one reason. After all, majority of the sea slugs involved in the study were infected with small crustaceans called copepods that interfere with reproduction. When the team studied another group of 64 E. atroviridis without these parasites, none chopped off their own heads—meaning that the critters may have ditched their bodies to be rid of the copepods once and for all.

With such a mindblowing discovery, the team is also seeking to uncover the secret to the disembodied heads’ survival. According to Mitoh, there could be stem-like cells at the neck capable of regenerating the rest of the body.

Moreover, the sea slugs are known to incorporate chloroplasts from the algae they eat into their own bodies, allowing them to fuel their own bodies through photosynthesis. This ability, called kleptoplasty, could be used by the slug heads to survive for nearly a month while undergoing regeneration.

“As the shed body is often active for months, we may be able to study the mechanism and functions of kleptoplasty using living organs, tissues, or even cells,” said Mitoh. “Such studies are almost completely lacking, as most studies on kleptoplasty in [sea slugs] are done either at the genetic or individual levels.”

Catch the sea slug in action below:

The article can be found at: Mitoh et al. (2021) Extreme autotomy and whole-body regeneration in photosynthetic sea slugs.


Source: Current Biology; Photo and video: Mitoh et al.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.

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