Planaria are common to many parts of the world, living in both saltwater and freshwater ponds and rivers. Some species are terrestrial and are found under logs, in or on soil. Others can be found on plants in humid areas.They play an important role in watercourse ecosystems and are often very important as bio-indicators.
Planaria have a solid body with no body cavity. The blunt, triangular head has two eye-spots, pigmented areas that are sensitive to light. There are two earlike projections at the base of the head, which are sensitive to touch and the presence of certain chemicals. They have single-opening digestive tract. Planaria eat living or dead small animals that they suck up with their muscular mouths. Planaria receive oxygen and release carbon dioxide by diffusion through the body wall.
There are sexual and asexual planaria. Sexual planaria are hermaphrodites, possessing both testicles and ovaries. Asexual planaria detaches its tail and each half regrows the lost parts by regeneration resulting in two worms.
Planaria can be cut into pieces, and each piece can regenerate into a complete organism. A piece of planaria, estimated to be as little as 1/279th of the organism, can regenerate into a complete organism over the course of a few weeks. The organism itself does not have to be completely cut into separate pieces for the regeneration phenomenon. If the head of a planarian is cut in half down its center, and each side retained on the organism, it's possible for the planaria to regenerate two heads and continue to live.
Tal Shomrat and Michal Levin have shown that planaria exhibit evidence of long-term memory retrieval after regenerating a new head.
Recent genetic screens have uncovered 240 genes that affect regeneration. Many of these genes have orthologs in the human genome. Planarian have a number of cell types, tissues and simple organs that are homologous to our own cells, and organs. Planarian have an apparently limitless regenerative capacity, and asexual animals seem to maintain their telomerase levels throughout their lifetime making them "effectively immortal".
Nature has answers to our questions about regeneration, aging and immortality. Feel free to use the knowledge!
Have fun and happy bug hunting :)