▁commonly ▁ground ▁for ▁mort ar ▁in ▁Central ▁America , ▁giving ▁raise ▁to ▁its ▁junior ▁syn onym , ▁" S . ▁calc ifer ". ▁ ▁Some ▁Mediter rane an ▁species ▁are ▁ed ible ▁and , ▁in ▁particular ▁S . ▁ga eder opus , ▁is ▁commonly ▁consum ed ▁in ▁S ardin ia . ▁Trop ical ▁species , ▁however , ▁tend ▁to ▁bio acc um ulate ▁sa x ito x in . ▁ ▁Species ▁Sp ond yl idae ▁tax onomy ▁has ▁under g one ▁many ▁revis ions , ▁mostly ▁due ▁to ▁the ▁fact ▁that ▁identification ▁is ▁tradition ally ▁based ▁on ▁the ▁shell ▁only , ▁and ▁this ▁is ▁highly ▁variable . ▁To ▁add ▁to ▁this , ▁while ▁some ▁shall ow - water ▁species ▁are ▁extremely ▁common , ▁at ▁least ▁two ▁deep - water ▁ones ▁ ▁are ▁known ▁from ▁a ▁single ▁spec imen , ▁while ▁a ▁third ▁( S . ▁gra vis ) ▁was ▁only ▁redis cover ed ▁after ▁ 7 7 ▁years . ▁At ▁least ▁another ▁common ▁species ▁( S . ▁reg ius ) ▁has ▁a ▁different ▁shell ▁when ▁it ▁grows ▁in ▁deep ▁water . ▁ ▁Sp ond yl us ▁amer ican us ▁Hermann , ▁ 1 7 8 1 ▁- ▁Atlantic ▁th orn y ▁o yst er ▁Sp ond yl us ▁an ac anth us ▁Ma we , ▁ 1 8 2 3 ▁- ▁n ude ▁th orn y ▁o yst er ▁Sp ond yl us ▁a on is ▁d ' Or b igny , ▁ 1 8 5 0 ▁Sp ond yl us ▁asi atic