| An extinct helcionelloid mollusk dissolved free from carbonate rocks in the lower Cambrian Mule Spring Limestone, Esmeralda County, Nevada. Specimen is greatly magnified, called scientifically Costipelagiella nevadense. Possible zoological affinities with gastropods, cephalopods, and monoplacophorans has been postulated by numerous investigators; nevertheless, they remain enigmatic constituents of the early Cambrian "small shelly fossils" category. Photograph courtesy a specific scientific publication. |