Problem of land snail pests in agriculture, by P.D. Srivastava. ISBN 978-8170224358 - An excellent book containing detailed information on snail biology and physiology as well as habitat.
Invertebrate Medicine, by G. Lewbart. ISBN 978-0813817583 - A very helpful guide to veterinary care for all invertebrates, including snails.
Behavior and its Neural Control in Gastropod Molluscs, by Ronald Chase. ISBN 978-0195113143 - A wonderful book looking at snail behaviour and biology. Looks at abilities such as magnoreception, vision and sensitivity. Highly recommended.
BSAVA Manual of Exotic Pets, Chapter 21: Invertebrates, by Romain Pizzi https://www.bsava.com/LinkClick.aspx?fileticket=t5GlxdHMmDY%3D&tabid=955&mid=2395 - An excellent guide to veterinary treatment for snails.