The term sibling species is often used in a technical sense to refer to the closest relative of a species, especially in the case of a split such as the closure of the isthmus of Panama, which separated Pacific and Caribbean populations.

Additional examples of species with nearly identical shells but different animals include Pleurobema beadlianum and Fusconaia askewi and species in the Crepidula plana complex.

    Dr. David Campbell
    Old Seashells
    University of Alabama
    Biodiversity & Systematics
    Dept. Biological Sciences
    Box 870345
    Tuscaloosa, AL  35487 USA
    [log in to unmask]

That is Uncle Joe, taken in the masonic regalia of a Grand Exalted Periwinkle of the Mystic Order of Whelks-P.G. Wodehouse, Romance at Droitgate Spa