The Obolellata are a class of Rhynchonelliform brachiopods with two orders, Obolellida and Naukatida. They are essentially restricted to the lower-middle Cambrian.[Streng, M., A. D. Butler, J. S. Peel, R. J. Garwood, and J.-B. Caron. 2016. A new family of Cambrian rhynchonelliformean brachiopods (Order Naukatida) with an aberrant coral-like morphology. Palaeontology, 59:269–293.]
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.[Balthasar, U. (2008). ~Mummpikia~ gen. nov. and the origin of calcitic-shelled brachiopods. Palaeontology 51, 263–279.]
Trematobolidae includes taxa such as Alisina, whose soft-part anatomy is partly known.
Anatomy
The shell is typically
impunctate,
biconvex shell, and oval or subcircular in shape. They are like other inarticulates in that, as with the
, 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.
[Lipps, Jere H.; Signor, Philip W. (January 1, 1992). Origin and Early Evolution of the Metazoa. Springer. . Page 417.] 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.
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