LIFESCI 1 Chapter Notes - Chapter 44: Comparative Embryology, Choanoflagellate, Germ Layer
Document Summary
The organisms most closely related to animals are choanoflagellates, a type of protist. This relationship was first proposed in the nineteenth century on the basis of cell shape and was confirmed in the twenty-first century by molecular sequence comparisons. Multicellularity differentiates animals from most choanoflagellates, which are unicellular, but multicellularity is not a unique feature of animals. Plants and fungi are multicellular as well. Animals are heterotrophs, gaining energy and carbon from preformed organic molecules. This character differentiates animals from plants, but not from fungi, which are also heterotrophs. Animals follow a pattern of early embryological development that includes gastrulation, a character not found in fungi or other multicellular groups. Animals can therefore be described as multicellular heterotrophic eukaryotes that form a gastrula during development. Other features, both molecular and biochemical, also distinguish animals from other organisms, but basic features of nutrition and development set the stage for considerations of animal diversity.
