▁of ▁commercial ▁value , ▁and ▁therefore ▁attempts ▁have ▁been ▁made ▁to ▁har vest ▁p ear ls ▁commer cially ▁from ▁many ▁different ▁P inct ada ▁species . ▁ ▁Character istics ▁ ▁The ▁species ▁is ▁small , ▁only ▁three ▁to ▁four ▁inches ▁in ▁diameter . ▁ ▁The ▁shell s ▁are ▁either ▁gray ish ▁or ▁green ish ▁yellow ▁and ▁surrounded ▁by ▁a ▁few ▁ind ist inct ▁brown ish - green ▁radial ▁bands . ▁ ▁N acre ▁is ▁t int ed ▁yellow ish - green , ▁with ▁a ▁slight ▁border ▁of ▁pale ▁yellow , ▁and ▁has ▁brown ▁mark ings . ▁The ▁shell ▁has ▁a ▁rounded ▁outline , ▁with ▁a ▁nearly ▁equal ▁height ▁and ▁width . ▁O yst er ▁shell s ▁are ▁usually ▁o val ▁or ▁p ear - sh aped , ▁but ▁will ▁vary ▁widely ▁in ▁form ▁depending ▁on ▁what ▁they ▁attach ▁to . ▁O yst ers ▁have ▁a ▁strong ▁inner ▁shell ▁layer ▁composed ▁of ▁n acre , ▁also ▁known ▁as ▁" m other ▁of ▁p ear l ". ▁An ▁o yst er ▁can ▁filter ▁ 1 . 3 ▁gall ons ▁of ▁water ▁per ▁hour . ▁ ▁Hab itat ▁and ▁distribution ▁Although ▁the ▁population ▁st ret ches ▁along ▁the ▁northern ▁coast ▁up ▁the ▁Great ▁Bar rier ▁Re ef , ▁P . ▁alb ina ▁is ▁pre domin ately ▁found ▁in ▁Sh ark ▁Bay , ▁Western ▁Australia . ▁P . ▁alb ina ▁th riv es ▁in ▁relatively ▁shall ow ▁waters , ▁which ▁contributed ▁to ▁its ▁being ▁the ▁first ▁Australian ▁p ear l ▁o yst er ▁discovered . ▁ ▁When