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Ventral valve, showing distinct sulcus
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Clavigera planchesi
Order: Brachiopod
Genus: Clavigera Species: Clavigera planchesi Location found: 88 Valley, Wakefield |
The Athyrid sequence that runs through the Triassic, with the genus Athyris in the Kaihikuan stage and Oxycolpella in the Oretian and Otamitan, is represented by a third genus in the last stages of the Triassic: Clavigera. The first member of this genus to appear was what is now called Clavigera planchesi, in the Warepan stage. The image above shows a specimen from 88 Valley, near Wakefield, set amongst pieces of the bivalve Monotis sp. - the key marker for the Warepan. Further images, from Southland, are shown to the right.
As these image indicate, Clavigera planchesi has clear morphological differences compared to the earlier Athyrids. The shape has become broader and oval, and there is a moderately long, straight hingeline, almost the width of the valve. There is also a well-defined sulcus on both ventral and dorsal shells (i.e. the species is bi-sulcate), flanked by marked folds. The commissure is, accordingly, more or less straight (i.e. unplicated). Both shells also show growth lines which become more marked towards the anterior margin of the shell. Ventral and dorsal valves are thus rather similar, though the latter tends to reveal a slightly more undulating outline. As with several other Athyrid species, there is some dispute about the identification and naming of C. planchesi. It was previously called Clavigera bisulcata, and was described by Trechmann (1917) under the name Hectoria bisulcata (see panel, right). All the features described by Trechman can be seen in the specimens shown here. Difficulties may also arise in distinguishing between Clavigera planchesi and its sister species C. tumida, which seemed to succeed it during the Otapirian stage. A complete gallery of Clavigera specimens in the collection, showing both species, plus ones attributed only to Clavigera sp. is shown here. This illustrates some of the variability seen in the genus, and some of the difficulties that can be encountered at trying to classify at the species level. Further Reading: Trechmann, C.T. 1917 The Trias of New Zealand. Quarterly Journal of the Geological Society 291, 165-246 (+ 10 plates). |
Ventral valve
Dorsal valve
Detailed description of Hectoria bisulcata (from Trechmann 1917) Shell rather wider than long, moderately inflated, the valves almost equally convex. The hinge-line is nearly straight, and represents the greatest width of the shell. The area is narrow and faintly striate parallel to the margin, and the ventral beak projects slightly above the area . . . The outline maintains the same width at the sides for some distance from the hinge-line, and then narrows to the anterior margin, which is gently rounded. In both valves two raised rounded ridges diverge from the beaks, and proceed towards the anterior margin meeting the similar ridges of the opposite valve. They enclose a shallow, rapidly-widening, triangular sulcus; but towards the anterior margin both ridges and suleus become weaker, and merge into the rounded surface of the shell. The junction of the shell is but slightly sinuous. |