The planarian has a soft, flat, wedge-shaped body that may be black, brown, gray, or white and is about a half inch (1.3 cm) long. Most are freshwater forms, but marine and terrestrial planarians does exist. The most common species studied in the lab is the brown planaria. Extreme heat or cold will harm planarians. Maintain a temperature of 69º to 72º F. Some planarians exhibit an extraordinary ability to regenerate lost body parts. For example, a planarian split lengthwise or crosswise will regenerate into two separate individuals. Each 2 oz. culture is enough for a class of 30.