In 1833, Robert Edmond Grant grouped sponges into a phylum he called Porifera (from the Latin porus meaning "pore" and -fer meaning "bearing"). The morphologies of spicules are often unique to clade- or even species-level taxa, and this makes them useful in taxonomic assignments. It is these skeletons that are composed of the elements called spicules. Among the four sub-clades of Porifera, three ( Demospongiae, Hexactinellida, and Homoscleromorpha) produce skeletons of amorphous silica and one ( Calcarea) of magnesium-calcite. Most sponges produce skeletons formed by spicules, structural elements that develop in a wide variety of sizes and three dimensional shapes. They are distributed globally, with diverse ecologies and functions, and a record spanning at least the entire Phanerozoic. Sponges are a species-rich clade of the earliest-diverging (most basal) animals. Some species obtain silica for building spicules by ingesting diatoms. Demosponges can also have siliceous spicules.
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