Obolellida

Obolellida
Scientific classification
Kingdom:	Animalia
Phylum:	Brachiopoda
Subphylum:	Rhynchonelliformea
Class:	Obolellata
Order:	Obolellida Rowell, 1965

Obolellida is a small, extinct order of inarticulate brachiopods that existed from the early to middle Cambrian period. The relationship of the Obolellida with other inarticulates is unclear, and were previously grouped together with the Siphonotretacea, before being given their own order.

Anatomy

The shell is typically impunctate, biconvex, and oval or subcircular in shape. They are like other inarticuates in that, as with the lingulids, the shell has no hinge, at least in the earliest examples.^[1] It is thought they may have used a hydraulic mechanism. However they later seem to develop a primitive articulation, in which some used a levator mechanism for opening the shell.^[2] At the posterior is a ventral valve with a defined flat-shelf. The pedicle opening can be positioned at various positions.^[3]

Notes

1. ^ Paleos, Order Obolellida. (URL accessed July 4, 2006).
2. ^ Lipps, Jere H; Signor, Philip W (January 1, 1992). Origin and Early Evolution of the Metazoa. Springer. ISBN 0-306-44067-9. Page 417.
3. ^ McGraw-Hill AccessScience, Obolellida. (URL accessed July 4, 2006).