Spiriferida

Spiriferida is an extinct order of brachiopods, known from the Ordovician to the Triassic.

== Description == The order Spiriferida belongs to the subphylum Rhynchonelliformea, approximately corresponding to the former subphylum Articulata (articulate brachiopods) characterised by calcareous shell with teeth and sockets, and to the class Rhynchonellata defined on the basis of the shell microstructure. thumb|Spirifer striatus, a Carboniferous spiriferide: the top image shows the dorsal view of an articulated shell; the bottom image shows the ventral valve (the dorsal one has been removed) allowing to notice the spiralium (laterally oriented cones forming the skeleton of the lophophore) The spiriferides are characterised by a spiralium (skeleton of the lophophore) that is oriented laterally or postero-laterally, the absence of a jugum (an element of the skeleton linking two spiralian cones), and an impunctate shell. The two latter characters allow the distinction between the orders Spiriferida and Spiriferinida (the latter having a punctate shell and a jugum). These two orders were merged in older brachiopod systems, which explains information about Jurassic spiriferides being found in older sources. The feature that gives both the spiriferides and the spiriferinides their name ("spiral-bearers") is the internal support for the lophophore; this brachidium (more precisely, a spiralium), which is sometimes preserved in fossils, is a thin ribbon of calcite that is coiled tightly within the shell forming a cone.