Earth Sciences 1083F/G Lecture Notes - Lecture 17: Paleozoic, Gastrulation, Pharynx

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The metazoa (differentiated multicellular animals): an overview of the major groups. Protista amoebas, foraminifera, radiolaria (presumed ancestors of metazoa) Cnidaria/coelenterata sea anemones, corals, sea pens, etc. Mollusca bryozoans ( moss animals ) snails, clams, cephalopods, etc. You have to start out simple: single celled protista. A choanoflagellate is a protist with a collared cell and a flagellum. No longer has to move around to find food. Once it is anchored, it can use its tail to move the water around and syphon food. Some choanoflagellates form colonies: in such colonies, all individuals cooperate in moving their flagella, generating a current from which food particles can be extracted. Phylum porifera (sponges): most basic metazoan body plan. Sponges also have collared cells, but these form a larger, integrated structure supported by rigid spicules or organic tissue: the differentiation of cells required the evolution of hox genes (genes that dictate differing functions of cells)

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