Heads of Elysia cf. marginata sea slugs sometimes pull themselves free from their bodies. The heads just keep crawling around. Within a few hours, some heads start nibbling algae again. Within about 20 days, heads from young slugs can have regrown those missing body parts, including heart and all.

Sayaka Mitoh and Yoichi Yusa are ecologists at Nara Women's University in Japan. They described the regrowth of cells and ultimately the sea slugs bodies March 8 in Current Biology.

Mitoh first noticed the sea slugs' extreme regeneration by chance. It showed up in some Elysia slugs in his lab. "We were really surprised to see the head crawling," Yusa says.

The head of a sea slug can take several hours to rip itself loose from its body. That's so slow that Mitoh and Yusa don't think the move helps slugs escape predators.

Instead, a detachable body could give the sea slug a drastic, but effective, way of fighting parasites. Mitoh monitored 82 E. atroviridis slugs infested with copepods. Three of the slugs ditched their bodies along with a lot of those copepods. Two of the three managed to grow a new body. An additional 39 of the parasitized slugs let parts of their bodies slowly fall away. In contrast, 64 more sea slugs that had been collected at the same time had no pests. And none of them threw away its body. That supports the idea that parasites could drive slug heads to detach and crawl away from their bodies.

What might help Elysia slug heads regrow a whole body is stealing, Yusa suggests. These animals can take the green sunlight-trapping energy factories called chloroplasts from algae. Very young slugs don't have any chloroplasts. "They need to pierce the cell walls of sea algae and sip the contents," he says. Once ingested, the chloroplasts remain alive inside the slugs for weeks to months.

Biologists have debated what stealing chloroplasts does for the slugs

Using what you know about cellular differentiation and the description of sea slug regeneration explain what is happening at a cellular level:?
A;Specialized cells undergo cellular differentiation to create stem cells that will grow and replace the old cells
B:Stem cells undergo cellular differentiation to create specialized cells to replace missing body parts like cardiac (heart) cells.
C:Cellular differentiation is not necessary in order for the sea slugs to regrow its missing body parts.
D:None of the above.