Berthella martensi is a species of sea slug, a marine gastropod mollusk in the family Pleurobranchidae.

The body is always marked with dark or clear spots, according to what is the dominant background color.

The mantle, which covers the body, is composed of four distinct parts: dorsal, anterior, and two lateral pieces protecting the gills.

This species has another means of defense by secreting a repellent acid fluid.

[2] It is usually found among rubble of dead coral in lagoons, or top of the external reef slopes, from the intertidal zone to 25 m depth.