Ontogenetic changes of the spiral cords as keys innovation of the muricid sculptural patterns: the example of the Muricopsis–Murexsul lineages (Gastropoda: Muricidae: Muricopsinae)

The primary cords of 68 species belonging to the Muricopsis/Murexsul lineages (Priabonian to Recent) are analysed. The study of their development allows distinguishing three derived sculptural patterns in Muricopsis and three in the Murexsul group. They appear late in the evolutionary history of the studied lineages, mainly in tropical waters. They are produced by heterochronies affecting precise cords by paedomorphosis, whereas others poorly evolved or may be hypermorphic. These results suggest that the phase of sculptural increase yielding the primitive pattern is followed by a selective phase, preserving or increasing the relief of the probable most functional cords.