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Dorsal valve; note the large pedicle opening in the ventral beak that faces upward
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Clavigera tumida
Order: Brachiopod
Genus: Clavigera Species: Clavigera tumida Location found: Southland |
Towards the end of the Triassic, the Athyrid species again changed, and in the Otapirian stage are represented by Clavigera tumida. Previously, the species was called Hectoria tumida by Trechmann (1917), who provided a detailed description under that name (see right).
Though broadly similar in outline to its predecessor, C. planchesi, Clavigera tumida can be distinguished from that species by its greater size and heaviness, its larger beak and foramen, and the weaker sulcation. The thick accumulation of shell that develops between beak and hingeline means that marked differences in the apparent shape occur between shelled and unshelled specimens. The beak, for example, is less prominent, and the straight hinge is masked by the sloping shoulders of the shell on either side of the beak. The specimens above, and to the top right are both from Southland (detailed location unknown). In the image above, the heavy beak and large foramen of the ventral valve are clear, extending beytond the margins of the smaller dorsal valve. The dorsal valve shows the broad, shallow sulcus. The image right shows the ventral valve and the moderately large beak and straight hingeline are both clear. The image below right is from Packers Creek, near Nelson. An internal cast of the ventral valve, this has several unusual features, including the stippling on the shoulders of the shell, either side of the beak. and the distinct bands that run parallel to the hingeline. A full gallery of Clavigera specimens included in the collection is shown here, which helps to illustrate the differences between C. tumida and C. planchesi. Further Reading: Trechmann, C.T. 1917 The Trias of New Zealand. Quarterly Journal of the Geological Society 291, 165-246 (+ 10 plates). |
Ventral valve
Ventral valve (internal cast)
Detailed description of Hectoria tumida (from Trechmann 1917) The interior of the ventral valve is considerably thickened posteriorly by deposition of shelly matter; the hinge-teeth are prominent, are supported by short dental plates, and there is a short median septum. In the dorsal valve the hinge-region is still more thickened; the cardinal process is very large and prominent, and consists of a blunt tongue-shaped mass of shell, which projects backwards beneath the delthyrial region of the ventral valve. The cardinal process has a shallow depression on its surface. In front of the cardinal process a deepened cavity projects backwards beneath it, and is divided by a rather high, blunt, median septum which separates the two adductor-scars. On each side of the cardinal process is a fairly-deep dental socket. The ovarian pittings, vascular impressions, and muscle-scars are well marked in both valves . . . |