Calcarea

Second only to the demosponges, calcareous sponges comprise a very immense division of the family tree.  In fact, there is more than 100 various genera of Calcareas.  Several have already perished into extinction such as the Heractinids.  A veritable plethora of attributes distinguish calcareous porifera from others of the phylum.  Most prominently, the spicules which preserve structure are composed of calcium carbonate crystals.   Heteractinids (which are extinct) displayed eight-rayed spicules, but modern species only manifest spicules with three or four rays.   Physically, the exterior colors of the sponges extend over a spectrum of pastels and some species manifest tan or gray.  Generally, calcareous porifera have achieved all three of the dimensions of construction: asconoidal, synconoidal, and leuconoidal (which is the most complex).    They often resemble pears, purses, or vases.  As a result of the composition of their crystals and their spicules, they appear bristly.
    Their diversity is due to their origination in the Lower Cambrian period.  While they were far more diverse during the Cretaceous period, there still exists a myriad of species.  These are divided between two subclasses, denoted as Calcaronea and Calcinia.  By the Cretaceous period, they had achieved immense diversity.  The diversity is immensely reflected in the tropical areas in shallow waters that are less than 1000 meters deep.  However, specimens have been discovered in waters to an extent of 4000 meters deep.  Despite their diversity, calcareous sponges are not extremely well-studied.  Due to their mysterious and differentiating "life styles"  and intriguing features, they have been extremely perplexing to marine biologists and other scientists.  They are integral complements to reef life.  Some porifera have been known to be the home of more than 16,000 other species that live within their body tissues. While frequently inhabiting the Barrier Reef, the various subclasses of the class are delineated to a myriad of world seas.  The subclass Pharetionidia is designated to the Mediterranean and Pacific.
    While they relate to each other as a result of calcareous composition, their divergence is extremely distinct.  The currently extant (but theoretical) subclasses are Pharetionida, Calcaronea, Calcinia, and Sphinctozoa.  Sphinctozoa is an extremely recent division, it was confirmed only in 1982.  Even more recent theories suggest that it is an entirely distinct class.  In a matter of weeks, this web site might even be obsolete.  (We hope that does not happen)  This only justifies the fact that our world is full of unfathomable wonders.  We only have to be willing to analyze.