SHELL --- F LIFE

Today as I blew the dust off these objects I got to thinking what a Collector of Shell's is ? I don't they just sort of Multiply. I guess its some sort of  ologist ? How do you tell the age of them ? The one in the centre belonged to my Mam when she was a child so it has to be over 100 years old. I never asked  how she came by it and she never went on holiday then. Do they have creatures inside like tortoises ? Did hers swim/run/walk or crawl from South Shields to Whitley Bay Beach or from somewhere more exotic like Fiji. I will never know :(