What are Nudibranchs?

Nudibranchs are a group of soft-bodied, marine gastropod molluscs which shed their shells after their larval stage. They are noted for their often extraordinary colours and striking forms. Currently, about 3,000 valid species of nudibranchs are known. The word "nudibranch" comes from the Latin nudus "naked" and the Ancient Greek bránkhia "gills".

Habitat

Nudibranchs occur in seas worldwide, ranging from the Arctic, through temperate and tropical regions, to the Southern Ocean around Antarctica. They are almost entirely restricted to salt water, although a few species are known to inhabit lower salinities in brackish water. Nudibranchs live at virtually all depths, from the intertidal zone to depths well over 700 m (2,300 ft). The greatest diversity of nudibranchs is seen in warm, shallow reefs, although a new nudibranch species was discovered at a depth near 2,500 m (8,200 ft).

Coloring

In the course of their evolution, nudibranchs have lost their shells, while developing alternative defence mechanisms. Some species evolved an external anatomy with textures and colours that mimicked surrounding invertebrate animals to avoid predators. Other nudibranchs have an intensely bright and contrasting colour pattern that makes them especially conspicuous in their surroundings.