Strophomenida

Strophomenida
An Ordovician strophomenid with encrusting inarticulate brachiopods (the craniid Philhedra) and a bryozoan.
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Brachiopoda
Subphylum:	Rhynchonelliformea
Class:	†Strophomenata
Order:	†Strophomenida Opik, 1934

Strophomenida is a large, extinct order of articulate brachiopods that existed from the lower Ordovician to the lower Jurassic period. It was the largest known order of brachiopods, encompassing over 400 genera, including the largest and heaviest of known brachiopod shells. The strophomenids lost the ability to attach by the stalk in adult specimens, so they either lay free, attached the ventral valve at the umbo to a firm substrate, or balanced with their spines sunken into a soft substrate. Typically the dorsal valve was either concave or flat, though occasionally it was convex; the ventral valve was convex. Typically, a member of this order was wider than it was long. In juveniles, there was a tiny hole at the animal's umbo for a stalk to emerge from. Tiny bumps cover the interior of the valves.

References

Thompson, Ida (1982). National Audubon Society Field Guide to North American Fossils. New York: Alfred A. Knopf. p. 648. ISBN 0-394-52412-8.

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  Strophomenid brachiopod with encrusting cornulitid tubeworm (Upper Ordovician, SE Indiana).]]
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  Strophomenid brachiopod Leptaena from the Upper Ordovician of Iowa.