Strophomenida
Strophomenida
Extinct order of brachiopods
Strophomenida is an extinct order of articulate brachiopods which lived from the lower Ordovician period to the mid Carboniferous period.[1] Strophomenida is part of the extinct class Strophomenata, and was the largest known order of brachiopods, encompassing over 400 genera[citation needed]. Some of the largest and heaviest known brachiopod species belong to this class. Strophomenids were among the most diverse and abundant brachiopods during the Ordovician, but their diversity was strongly impacted at the Late Ordovician mass extinction. Survivors rediversified into new morphologies in the Silurian,[2] only to be impacted once again at the Late Devonian mass extinction. However, they still survived till the mid Carboniferous.[1]
Adult strophomenids lack an opening for the pedicle (stalk), so in life, they either lay free or cemented the ventral valve (lower shell) onto a firm substrate at the umbo (hinge). In juveniles, a tiny hole for the pedicle was present on the ventral valve near the umbo, but this is closed up through development. The dorsal valve was typically concave or flat, though occasionally it was convex; the ventral valve was always convex. The hinge line at the rear of the shell was quite wide and strophic in shape, meaning that it was nearly straight. Many strophomenid shells are wider than long. The interior of the valves have a distinctive pseudopunctate microtexture: deflections in the mineralized shell layers stack up and unfurl into tiny bumps, which are usually supported by calcite rods known as a taleolae.[3]
