Figure 31.14 Mollusks in Some Groups Have Lost Their Shells (A) Nudibranchs (“naked gills”), also called sea slugs, are shell-less gastropods. This species is brightly colored, alerting potential predators of its toxicity. (B) Slugs are terrestrial, shell-less gastropods that feed on decomposing vegetation on the damp forest floor. (C) Octopuses have neither an external nor an internal shell, which allows these cephalopods to squeeze through tight spaces.