Brachiopods are often confused with modern-day bivalves, which are molluscs. Indeed, well into the 20th century, brachiopod classifications were based on a supposed close relationship with the molluscs. A full classification of the inarticulate brachiopods, after Williams (1996) can be seen below. The 3rd brachiopod subphylum, the Rhynchonelliformea, are articulate brachiopods and are not shown here. After this classification, the strict division of brachiopods into 'articulate' and 'inarticulate' ceased, and the inarticulate brachiopods were roughly subdivided amongst the subphyla Linguliformea and Craniiformea (highlighted in bold). Those taxa now extinct are indicated by an asterix (*). Of the 4,500 or so known brachiopod genera, 95% are now extinct. This fact has made it quite difficult in the past to ascertain relationships within the phylum. Indeed there are some who believe that the subphyla are polyphyletic, having arisen separately and without a common ancestor.
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