Printed

Slugs of Britain & Ireland: Identification, Understanding & Control by Ben Rowson, etc (FSC Aidgap, 2014) 

Land Snails of the British Isles by Robert Cameron (FSC Aidgap, 2003)

Freshwater Snails of Britain & Ireland by Ben Rowson, etc (FSC Aidgap, 2021)

Websites

Google Lens: Go to google.com and there is a camera icon at the right of the search bar. Click on this, and you can drag and drop any image and it will do its best to identify it – so can be used for any flora and fauna, vertebrates and invertebrates etc. (as well as buildings, landscapes – anything, in fact.)  Worth a look, but treat identifications with caution!

Apps