A new theory to explain the origin of growth lines in sea urchin spines

Abstract

A new theory IS proposed to explain the origln of some growth lines in echinoid splnes. It is proposed that lines form as part of a growth event initiated when a usually non-growing spine no longer fits the growing tubercle on which it sits. Growth lines also can form in response to damage but neither cause of growth lines is periodic and hence lines cannot be used to determine age.