6 Flatworms Turbellaria and nemertea

Turbellaria and Nemertea are common, and often very numerous inhabitants of freshwaters. Even though more than 200 species of Turbellaria and three species of Nemertea live in North America, their ecology and systematics have been less studied than that of many other common aquatic invertebrates. An obvious reason for this limited attention is the difficulty posed by preservation. Most turbellarians become unrecognizable after a routine preservation of field samples in alcohol or formalin. Study of live specimens is the best method, and many interesting discoveries lie ahead in the areas of reproductive biology, dispersal, endosymbiosis, and community structure. In view of the limited knowledge of nemertean ecology, almost any area of research provides valuable information. New information on phenology, population dynamics, and habitat selectivity would permit a better evaluation of the role of nemerteans in freshwater communities. Specific studies in the biology of nemerteans appear particularly promising in the areas of reproductive biology and evolutionary ecology. The ecological role of femaleness later in the life cycle, the production of resting eggs, and the environmental versus genetic cues of life stages may offer exciting and general models for evolutionary ecology.