Bellerophontoidea

The Bellerophontoidea, (Bellerophontaceae Ulrich & Schofield, 1897, ex Bellerophontidae McCoy 1951), common name "bellerophonts", is a superfamily of extinct planospirally-coiled globose molluscs. This superfamily is generally included within the Gastropoda, but may instead be a group of monoplacophorans. The taxon first appeared late in the Cambrian and continued until late in the Triassic.

Biology

Unlike normal gastropods, the shells of Bellerophonts are characterised by a completely planispiral pattern of coiling, such as one finds in shelled cephalopods. Experts disagree whether Bellerophontids should be classified as torted gastropods, or as untorted Tergomya, or whether the group Bellerophontida is perhaps an artificial construct, consisting of a number of distinct groups of Palaeozoic molluscs which evolved the same type of spiral shell independently.

J.B. Knight, et al. (1960) regarded the bellerophontids as torted gastropods even though they have essentially symmetrical, planispiral shells.