Complex sentence: The molluscs that were placed in this order have a heterostrophic protoconch, where the whorls at the peak of the spire are coiled in an opposite direction to the adult whorls.
Split into simpler sentences: The molluscs that were placed in this order have a heterostrophic protoconch. This is where the whorls at the very peak of the spire of the shell are coiled in an opposite direction to the adult whorls.