Facelinidae Nudibranchs are colourful aeolid nudibranchs found at all dive sites around Koh Lanta.
Members of the superfamily of aeolid nudibranchs have many tapered blood-filled tubes growing from the dorsal (back) and lateral (side) areas of the body. These growths are called 'cerata'.
Cerata perform several functions and contain a duct of the digestive gland. These thin-walled, blood-filled structures also act as gills, and for those species eating corals and anemones, there is a poisonous stinging sac at the tip of the cerata used for defence.
Since a large part of the colour of these nudibranchs depends on the colour of the cerata, which in turn are also influenced by the diet, members of this family can change colour depending on what they eat.
Facelinidae Nudibranchs usually have a long, extended body (elongate), with the cerata usually arranged in arches or rows. Most species of this family feed on hydroids, from which they extract the stinging chemicals for use in their defensive stinging sacs.