Seashell: Venus Comb shell
This murex is called Venus Comb (Murex Pecten). It is one of the exceedingly exotic and beautiful ones.
This one is bought in San Francisco, California, USA, in 2002. (the label says it came from the Philippines.) Measures 13 cm.
Seashells are developed from the cacium deposits of the mollusk. I can't imagine how it grows spines as these.