Science Snippet: Planarian Worms

Planarian worms are carnivorous little flatworms that live in dark places in ponds and streams. Cute little creatures 3-15 mm long with crossed eyes, they glide around on their undersides searching out large protozoa, tiny snails, and other small worms. Students in biology labs often get to see these little creatures, where they learn that the crossed eyes perceive only light and dark. These simple appearing animals, however, have some amazing qualities. Cut them into several pieces, and after about 10 days the pieces regenerate a new planarian, complete with a new head and tail. This is possible because about 20 percent of their cells are “pluripotent” stem cells, or cells that can become a variety of tissue types. Another amazing thing about planaria is that they can “learn” in spite having a brain about a quarter the size of the period at the end of this sentence. Researchers at Tufts University, knowing they dislike light and open spaces, trained them to accept food in the lighted center of a Petri dish. This required about 10 days of training. Researchers cut off the heads of trained worms and removed all traces of their brain. After 14 days of recovery, the worms regenerated new heads. When these were tested in a Petri dish with lit food in the center, after one day they somehow “remembered” that the light presented no danger and crawled across the open space to the lighted center and ate the food. Could it be that parts of the body other than the head have the capacity to remember? Research continues in an effort to find out. (T. Shomrat and M. Levin, 2013, Journal of Experimental Biology, July 2; theverge.com/2015/3/18/8225321/memory; many other sources)