• Source: Obolellata

The Obolellata are a class of Rhynchonelliform brachiopods with two orders, Obolellida and Naukatida. They are essentially restricted to the lower-middle Cambrian.




Obolellida


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.
One representative, Mummpikia, has been linked to the origin of calcitic shelled brachiopods more generally, hinting that obolellids may be paraphyletic.
Trematobolidae includes taxa such as Alisina, whose soft-part anatomy is partly known.




= Anatomy

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The shell is typically impunctate, biconvex, and oval or subcircular in shape. They are like other inarticulates in that, as with the lingulids, the shell has no hinge, at least in the earliest examples. 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. At the posterior is a ventral valve with a defined flat-shelf. The pedicle opening can be positioned at various positions.




Naukatida


Some of these are coral-like creatures.




References


Key reference: Popov, Leonid E.; Holmer, Lars E. (2000). "Class Obolellata". Treatise on Invertebrate Paleontology. Vol. Part H Brachiopoda. University of Kansas Press. pp. 200–215. ISBN 0-8137-3108-9.

Kata Kunci Pencarian:

• Obolellata
• Rhynchonelliformea
• Brachiopod
• List of bilaterian orders
• Alisina
• 2016 in paleontology
• Treatise on Invertebrate Paleontology
• Nasakia
• Obolella