page_title: Calcareous sponge
section_title: Classification
hierarchical_section_title: Calcareous sponge / Classification
caption_attribution_description: English: Clathrina clathrus (Sicily, Tirrenian Sea)
context_page_description: The calcareous sponges of class Calcarea are members of the animal phylum Porifera, the cellular sponges. They are characterized by spicules made out of calcium carbonate in the form of calcite or aragonite. While the spicules in most species have three points, in some species they have either two or four points.
context_section_description: Of the 15,000 or so species of Porifera that exist, only 400 of those are calcareans.
  Calcarean sponges first appeared during the Cambrian, and their diversity was greatest during the Cretaceous period. Recent molecular analysis suggests the class Calcarea should be designated as a phylum, in particular the first to have diverged in the Animalia.
  The calcareous sponges are divided into two subclasses and six orders:
  Class Calcarea
  Subclass Calcinea
  Order Clathrinida
  Order Murrayonida
  Subclass Calcaronea
  Order Baerida
  Order Leucosolenida
  Order Lithonida
  Order Pharetronida†
caption: Clathrina clathrus, an asconoid calcareous sponge
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