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Unformatted text preview: or from fragments) or sexually . Sponges produce eggs and sperm that are released into a central cavity of the sponge, in which the zygote develops into a ciliated larva. The larval stage is able to move about while the adult is stationary. The fossil record of sponges has been at times quite good. The oldest sponges date from the precambrian. One early example of fossil sponges are the archaeocyathids, one of the first reef-building animals. Archaeocyathids evolved and went extinct before then end of the Cambrian Period. Cladistic analysis by J. Reitner in 1990 suggests archaeocyathids are properly placed in the Phylum Porifera instead of having their own phylum. Living sponges fall into three groups: the calcareous (an example of which is shown in Figure 9), glass, and demosponges, based on the chemical composition of spicules....
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- Fall '10
- Biology, Phylum, Phylum Porifera, Budding