Bellerophontoidea

Bellerophon sp. (Bellerophontoidea: Bellerophontidae) † Bellerophontidae), at the Paläontologische Museum München. Photo by Ghedoghedo, Creative Commons Attribution Share Alike/GNU Free Documentation License, via Wikipedia.

The Bellerophontids are another of those many fascinating lineages of Paleozoic molluscs previously included under the wastebasket taxon "Amphineura", whose evolutionary relationships are difficult to determine from examination of the shell alone. Unlike the helcionelloids they were common and long-lived, ranging from the Ordovician to the Triassic. Their shells are planispiral (coiled along a single plane) which makes them similar in appearance to tiny nautiloids, although they can be distinguished by a lack of septa and siphuncle. The tendency seems to be to consider bellerophontids as basal or stem-group gastropods, although there is no agreement as to whether they underwent torsion as true gastropods do. Here we propose that many bellerophontids were torted, and hence gastropods (albeit more primitive than any living gastropods), whilst other molluscs with very similar shaped shells were untorted, and hence non--gastropod conchiferans MAK120617