Most are sponges are asymmetrical, though some of them exhibit radial symmetry (Dawkins 2004). As an adult they may have multiple cell layers, but initially they all arise from the two layers that were present in the early embryo (Dawkins 2004). They are known be diploblast, which means having two layers of cells (Dawkins 2004). Like plants they move at the cellular level (Dawkins 2004). They stay put in one place stuck to the bottom of the water- either salt or fresh. Like plants they do not move, i.e., they are sessile. This misconception is due to some of the characteristics of the Porifera (Dawkins 2004). People often think of sponges as plants, rather than being animals. Some molecular taxonomists think that there are two lineages of sponges, one more closely related to other more complex Metazoans than the other. Today the rest of the Metazoans are considered to belong to Eumetazoa. For a long time they were written off as ‘parazoa’. Sponges are the first and most simple members of Metazoa in the ancestral lineage of animals (Dawkins 2004).
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