2. #507 Girtyocoelia. This little Paleozoic sponge is calcareous. It grew in bulbous chambers around a central tube, as shown in the diagrams. 3. # 2004 Astraeospongia. Another Paleozoic calcareous ...

The early growth stages of other fossil sponges also reveal the same symmetry, where there is no obvious symmetry in the adults. There is even a trace of this symmetry known in living calcareous ...

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London : Henry S. King & Co., 1876. Illustration on facing page: Development of Calcareous sponge (Olynthus). Image and original data provided courtesy of the National Library of Medicine; Please be ...