Phylum Porifera Essay

Words: 1051
Pages: 5

1Department of Biology, College of Science, University of the Philippines Baguio
July 17, 2012

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|Sponges [Porifera] are unusual animals whose body plans make interpreting phylogenetic relationships within the group and with other basal |
|metazoan taxa a difficult task. In this exercise, different species of Poriferans were observed. It will be used then to determine their |
|defining characteristics as an invertebrate. The skeletal elements of the Poriferans, the spicules, are formed enzymatically by
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This system is found in Calcarea and Hexactinellida.

And lastly, the leuconoids which have the most complex structure. They have many small ostia. The ostia lead to numerous incurrent canals, but there is no large central cavity.

1.d) The skeleton of spicules and spongin provides the support to keep the pores open. The spicules can be either siliceous or calcareous of a variety of shapes, and can be used in identifying species. The spongin is a form of collagen.

1.e) The spicules are secreted by specialized mesenchyme cells known as scleroblasts. Scleroblast secreting a calcareous spicule is called calcoblast while that producing a siliceous spicule is called silicoblast. Monaxon spicules are formed because of the incomplete division of scleroblast cell giving rise to binucleate scleroblast. The two nuclei begin to move away from each other and calcium carbonate from sea water begins deposit in between the space of two nuclei in the form of an axis. As the calcium carbonate needle between the two nuclei begins to lengthen, the cell divides into two, the founder cell and the thickener cell. When the spicule is fully formed both the cells detach and wander off into mesenchyme. Triradiate spicules are secreted by three scleroblast cell which come to lie in a triangular manner. While the formation of sponging goes like this: Spongin fibres are