▁The ▁external ▁surfaces ▁of ▁the ▁shell ▁are ▁dark ▁brown ish ▁black ▁while ▁the ▁interior ▁of ▁the ▁shell ▁is ▁pur pl ish - black . ▁The ▁two ▁hal ves ▁of ▁the ▁shell ▁are ▁equal ▁in ▁size ▁and ▁similar ▁in ▁shape , ▁being ▁el ong ated ▁and ▁asym met rical , ▁with ▁a ▁d ys od ont ▁h inge ▁between ▁the ▁val ves . ▁The ▁sculpt ure ▁of ▁the ▁val ves ▁consists ▁of ▁numerous ▁fine ▁radial ▁b if ur c ating ▁rib s , ▁which ▁become ▁co ar ser ▁posterior ly ▁and ▁fin ely ▁scal loped ▁towards ▁the ▁edge . ▁The ▁outline ▁is ▁my til iform ▁with ▁a ▁terminal ▁um bo , ▁but ▁the ▁shape ▁is ▁very ▁variable ▁and ▁spec im ens ▁may ▁be ▁highly ▁expanded ▁posterior ly , ▁occasionally ▁cur ved ; ▁sometimes ▁almost ▁cyl ind rical ▁with ▁the ▁be aks ▁being ▁sub - term inal . ▁The ▁animal ▁is ▁attached ▁to ▁the ▁substr ate ▁by ▁thick ▁by ss us . ▁ ▁Hab itat ▁Bra ch id ont es ▁ph ara on is ▁is ▁found ▁on ▁rock y ▁substr ates ▁and ▁man ▁made ▁structures ▁in ▁the ▁inter tid al ▁zone . ▁They ▁appear ▁to ▁be ▁able ▁to ▁toler ate ▁wide ▁temperature ▁variations ▁in ▁their ▁invas ive ▁Mediter rane an ▁range , ▁but ▁low ▁winter ▁temper atures ▁may ▁in hib it ▁their ▁phys i ology . ▁In ▁the ▁cool er ▁waters ▁of ▁the ▁western ▁Mediter rane an , ▁B . ▁ph ara on is ▁is ▁restricted ▁to ▁habit ats ▁with ▁higher ▁temper atures ▁and ▁sal