>If it is an egg case, is it the product of one female, or is it some kind of nursery?<
A single female produces each chain. I don't know the minimum size for reproduction in whelks, but the largest individuals can exceed a foot in length.
Dr. David Campbell
Old Seashells
University of Alabama
Biodiversity & Systematics
Dept. Biological Sciences
Box 870345
Tuscaloosa, AL 35487-0345 USA
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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