Likely to be cyclic expressions of growth like the annular rings on trees. And therefore probably tied to environmental factors as you observed. -----Original Message----- From: Peter Froehlich <[log in to unmask]> To: [log in to unmask] <[log in to unmask]> Date: Sunday, May 10, 1998 10:00 AM Subject: Growth scars >Can anyone tell me what would cause growth scars in gastropods? >At a beach where I often go shelling there is a population of Ilyanassa >obseleta. All of these shells seem to have a growth scar in the same >location on the shell, about 5-6mm back from the lip. Would environmental >changes create these kind of scars? I have also observed the same type of >scars on Nucella lapillus which live nearby but they don't seem to effect >as large a proportion of that population. But I haven't observed the same >type of scars on the Lunatia heros (moon snails) also found at this beach. >The scaring only seems to occur on species which inhabit the various >intertidal areas - mudflats and intertidal rocks. I apologise for not >checking the Littorina littorea (common european periwinkles)- I regard >them as the intertidal equivalent of dandilions. > >Since N lapillus (dog winkles) and I. nassa (mud nassa's) occupy very >different microenvironment's I am thinking that the cause must have been >environmental such as a sudden change in food supply or other environmental >conditions (water salinity? temperature? storm damage? ). I don't think >that it would have been a predator causing physical damage to the shells as >I don't think the scars would have been that even (scars form a straight >line and are located in the same place on the shells). > >If it is likely to have been an environmental change is there anyway to >determine how long ago it took place from the amount of shell whorl laid >down after the scar? > >Any thoughts or theories on this would be welcome.