Sucky snails: Sap-sucking slugs eat seaweeds and algae. Unlike many other snails, they don't tear up their food into little bits. Instead, they use their radula to pierce the cells of the seaweeds and algae and suck out the contents. The Leaf slug eats Sea lettuce (Ulva spp).

Stolen food factories: Some sap-sucking slugs retain the algae's chloroplasts (the part that contains chlorophyll). These chloroplasts continue to carry out photosynthesis inside the slug and provide the slug with extra nutrients.

Sap-sucking slugs belong to the same larger Subclass as nudibranchs and are sometimes mistaken for them.