Final answer:
Noncoelomate invertebrates like sponges and jellyfish are important in evolutionary terms because they represent key stages in the development of multicellular organisms. Sponges show a basic level of organization, while jellyfish demonstrate the emergence of true tissues, leading to the diversity of more complex animal life.
Step-by-step explanation:
Noncoelomate invertebrates, such as sponges and jellyfish, and noncoelomate worms, are evolutionarily important because they represent crucial stages in animal evolution. Sponges are significant as they are part of the Phylum Porifera and are considered the simplest of multicellular organisms, akin to what might be the ancestors of animals. They show basic organizational levels and carry out physiological functions typical of more complex animals. On the other hand, jellyfish, part of Phylum Cnidaria, represent the evolution of true tissues and a more complex level of organization compared to Porifera.
They mark a pivotal point in the evolutionary history of invertebrates by developing specialized cells and functions, which are precursors to organs and organ systems seen in more advanced life forms. This evolutionary lineage ultimately paved the way for the emergence of creatures with true differentiated tissues (Eumetazoa) and later, the diversity of animals we see today. Furthermore, the similarities between the choanocytes in sponges and choanoflagellate protists suggest a common ancestry for multicellular animals, indicating a significant evolutionary relationship.