We start our look at the animal kingdoms diversity at the start of its diversity. Sponges are the simplest animals we know of, very few specialized cells, maybe tissues, but no organs or organ systems. As we move up through the ranks of invertebrates things will become more complex: body cavities will become digestive systems, nerve nets will become nervous systems, more and advanced sensory organs will develop. That is the journey, let's begin at the start.
Compare and contrast sponges, cnidarians, and worms.
Contract 7 has you choosing a unique species of simple invertebrate to present to class: the four characteristics it shares will all living things, but how your animal shows them differently, how we classify your organism and by what traits, and where your species fits in the trends of growing complexity of invertebrates.
