Bellerophon (mollusc)
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Bellerophon is a genus of extinct, mostly Paleozoic snail-like mollusc of the order Bellerophontida. It is characterised by a globose, convolute, planispiral (symmetrically coiled) shell, which resembles a miniature cephalopod (e.g. Nautilus or ammonite), except that septa are lacking. The shell is usually a couple of centimers in length or diameter; the surface smooth, ornamented only by growth lines. There is a low crest or ridge running along the midline of the shell. The genus occurs world-wide, and is known from the Silurian to the Early Triassic periods. (Knight et al 1960)
Representative species include:
- B. vasulites Montfort - the type species, from the Middle Devonian of Germany
- B. graphicus Moore from the late Pennsylvanian (Virgilian) of Kansas
- B. regularis (Waagen) from the Permian of India
as well as many others.
Although usually classified as a primitive gastropod, there is a minority view that the Bellerophontida actually represented a more primitive, untorted type (see Torsion) that evolved a spiral shell independently. Another view is that some Bellerophontids, including Bellerophon, were torted gastropods, but others were untorted forms. (Wagner, 2001 p.1130)
Many specimens of Bellerophon show a "waterline" about half-way up the shell, suggesting that a large amount of the mantle and foot were exposed and covered the outside of the shell, as in the extant Cypraeidae and Naticidae. These animals were probably quick moving, relying on speed to avoid predators and, when this was not possible, withdrawing deeply into the shell. (Linsley 1978 p.201)
[edit] References
- Knight, J. B., Cox, L. R., Keen, A. M., Batten, R. L., Yochelson, E. L., and Robertson, R. (1960). Systematic descriptions [Archaeogastropoda]. In Moore, R. C. (ed.) Treatise on Invertebrate Paleontology. Part I. Mollusca 1, Geological Society of America and Kansas University Press, Colorado and Kansas.
- Linsley, R. M. 1978. Locomotion rates and shell form in the gastropoda. Malacologia 17, 193-206
- Moore, R.C., Lalicker, C.G., and Fischer, A. G., 1952, Invertebrate Fossils, McGraw Hill Book Company, New York; 766 pp.
- Wagner, P. J. 2001 Gastropod phylogenetics: progress, problems and implications. Journal of Paleontology 75: 1128 - 1140
[edit] External links
- Bellerophontida - Palaeos
