ag os ▁Islands . ▁They ▁live ▁from ▁the ▁low - t ide ▁line ▁to ▁ ▁deep .. ▁These ▁are ▁bottom ▁dwell ers , ▁favor ing ▁rock y ▁substr ates ▁and ▁re ef s . ▁ ▁Life ▁History ▁ ▁This ▁ur chin ▁see ks ▁holes ▁and ▁cre v ices ▁in ▁the ▁bottom ▁when ▁rest ing . ▁The ▁rock ▁protect s ▁them ▁from ▁pred ators ▁on ▁all ▁sides ▁except ▁the ▁opening ▁of ▁the ▁hole , ▁and ▁the ▁sp ines ▁guard ▁that . ▁ ▁When ▁an ▁individual ▁finds ▁an ▁especially ▁good ▁fitting ▁hole , ▁it ▁can ▁bra ce ▁its ▁sp ines ▁against ▁the ▁sides ▁of ▁the ▁rock ▁to ▁resist ▁being ▁pulled ▁out ▁of ▁its ▁n iche . ▁ ▁Crown ed ▁sea ▁ur ch ins ▁are ▁no ct urn al , ▁for aging ▁within ▁a ▁few ▁meters ▁of ▁their ▁sh el ters , ▁to ▁which ▁they ▁return ▁at ▁dawn .. ▁They ▁are ▁mostly ▁car n iv orous , ▁feed ing ▁on ▁sp ong es , ▁t unic ates , ▁b ry oz o ans , ▁and ▁alg ae . ▁▁ ▁Crown ed ▁sea ▁ur ch ins ▁are ▁g on och or ic , ▁which ▁is ▁to ▁say ▁that ▁there ▁are ▁two ▁sex es , ▁and ▁each ▁individual ▁is ▁either ▁male ▁or ▁female . ▁ ▁Sp aw ning ▁takes ▁place ▁on ▁a ▁month ly ▁cycle ▁that ▁may ▁be ▁tied ▁to ▁tid al ▁rh yth ms . ▁ ▁References ▁ ▁External ▁links ▁▁▁ ▁Category : Anim als ▁described ▁in ▁ 1 8 6 7 ▁Category : D ia dem