Sea slug

Still, the color can warn other animals of the sea slug's toxic stinging cells (nematocysts) or offensive taste.

Most sea slugs have a pair of rhinophores—sensory tentacles used primarily for the sense of smell—on their head, with a small eye at the base of each rhinophore.

One very unusual group of marine gastropods that are shell-less are the pulmonate (air-breathing) species in the family Onchidiidae, within the clade Systellommatophora.

[8] Like many nudibranchs, Glaucus atlanticus can store and use stinging cells, or nematocysts, from its prey (Portuguese man o' war) in its finger-like cerata.

[9] Other species, like the Pyjama slug Chromodoris quadricolor, may use their striking colors to advertise their foul chemical taste.

Headshield slugs, like the Chelidonura varians, use their shovel-shaped heads to dig into the sand, where they spend most of their time.

Peronia indica is a species of air-breathing sea slug, a shell-less marine pulmonate gastropod mollusk in the family Onchidiidae.

[11] Most sea hares have several defenses; in addition to being naturally toxic, they can eject a foul ink or secrete a viscous slime to deter predators.