Hibernating snails seal their opening with an “epiphragm,” a layer of dried mucus. (© Victoria Tucholka / Shutterstock)

Variations of the Cuban Painted snail, Polymita picta. (© Mark Brandon Shutterstock)

Earthworm movement. Each square represents a segment in either restricted or relaxed position. (Mokele/Wiki; cc by 3.0)

Earthworm labeled clitellum Holger Casselman Wikimedia CC BY-SA 3.0Lumbricus_rubellus_HC2

© Borbely Edit / Shutterstock.

Snail eating a carrot. (twistypigeon / Flickr; cc by 2.0)

Green Snail, Rhinocochlis nasuta. (Bernard Dupont) / Wiki; cc by-sa 2.0)

A snail’s eye. (Mac Jewell / Flickr; cc by 3.0)

Land snail (Euglandina Rosea). (Tim Ross / Wiki; PD)

Slug and slime trail. (Luis Parravicini / Flickr; cc by-nc-sa 2.0)