The Position of Acoelomorph Turbellarians Among Lower Worms

The Acoelomorpha is a group of worms of comparatively simple structure, and, accordingly, some biologists consider them to represent the most basic form of all multicellular animals. Acoelomorphs digest their food with a multinucleate mass of tissue instead of in the lumen or cavity of a gut, and their nervous system is only loosely organized into concentrations that could be compared to the brain and nerve cords of other animals. Taxonomists divide the group into 17 families, largely on the basis of the structure of the reproductive organs, but have fallen short of explaining how these families relate to each other or to other animal groups, including other flatworms. To better understand how these basic animal forms fit into the system of lower animals, members of the Acoelomorpha and other invertebrates believed to be related with electron and fluorescence microscopy, specifically looking at the musculature of the body wall and reproductive organs and the fine structure of the complexes of glands and sensory organs in the head. The characters discerned through this examination will then be applied to reconstructing relationships among acoelomorph families and relationships of acoelomorphs to other lower invertebrate groups. The ultimate goal of this research is to understand the causes of the diversity of these lower worms. This study will contribute to our understanding of the relationships of a very primitive or simple group of animals and will help clarify or explain radiations of many groups in the animal diversity of the earth