The planarian species often referred to as "immortal" is Schmidtea mediterranea. This particular type of planarian, a flatworm, has remarkable regenerative capabilities. It can regrow its entire body from just a small fragment of tissue, making it a fascinating subject for biological research, particularly in the fields of regenerative medicine and stem cell biology.

The "immortality" of Schmidtea mediterranea is largely due to its high concentration of pluripotent stem cells, known as neoblasts, which can differentiate into any type of cell in the worm's body. This allows the planarian to regenerate lost or damaged tissue and even reproduce asexually through fission.

• Use a clean, flat-bottomed container, such as a glass or plastic dish, or a small aquarium.
• Ensure the container has a tight-fitting lid to prevent escape and maintain humidity.

• Line the bottom of the container with filter paper or a thin layer of fine-grained aquarium sand.
• Avoid using soil or coarse substrates that could harm the planarians.

• Fill the container with dechlorinated or spring water to a depth of about 5-10 mm. Planarians need a shallow layer of water to move around and absorb oxygen.
• Change the water regularly (every 2-3 days) to prevent fouling and maintain water quality.

• Maintain the temperature between 18°C to 22°C (64°F to 72°F). Avoid extreme temperatures, as planarians are sensitive to heat and cold.

• Planarians are photophobic, meaning they avoid light. Keep the container in a shaded area or cover it with a dark cloth or lid to provide a low-light environment.

• Feed Schmidtea mediterranea small amounts of organic material, such as cooked liver, egg yolk, or brine shrimp.
• Place the food in the container and allow the planarians to feed for a few hours before changing the water.
• Feed them every 2-3 days, but do not overfeed, as excess food can foul the water.

• Clean the container regularly to remove waste and uneaten food.
• Monitor the planarians for any signs of stress, such as lesions, discoloration, or unusual behavior.