Evolution
Sponges as Phylum Porifera date as far back as the Cambrian and Ordovician period. The three major Phylum all appear to have developed around the same time. It is speculated that Porifera is a sister taxon to Choanoflagellata, due to the presence of aggregated groups of choanocytes inside the sponge body (Rupert et al 2009).
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Fossil records indicate several other major groups of sponges, many of which favoured a calciferous reef building type structure over the typical spicule skeleton. However time appears to have favoured the spicule cast of sponges (Reitner.J 1991).
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