The gastropods, more commonly known as snails and slugs are among the few groups of animals to have become successful in all three major habitats: the ocean, fresh water, and land.
Gastropods are characterized by the possession of a single (often coiled) shell into which the animal can generally withdraw, although this is lost in some slug groups.
Slugs are snails whose shells have been reduced to an internal fragment, shed after their larval stage (Nudibranchs) or completely lost in the course of evolution.
There are over 3,000 recorded Nudibranch species, and these are noted for their often extraordinary colours and striking forms. Nudibranchs are often seen at many of the dive sites around Koh Lanta.
Some gastropods are scavengers, feeding on dead plant or animal matter; others are predators; some are herbivores, feeding on algae or plant material.
False cowries are a family of snails which live on, and prey on corals, particularly soft corals and sea fans. These snails are sometimes considered external parasites, as they can attach themselves to soft corals with their molluscan foot, and then slowly devour the coral polyps.
Wart Slugs are well known at all dive sites around Koh Lanta and are instantly recognisable by the warty mantle and lack of dorsal gills. Most species look similar and are black and white, with a possible third colour usually being yellow or orange.
The Chromodorid Nudibranchs comprise around 600 species and are among the most strikingly coloured and elaborately patterned of all animals. Chromodorid Nudibranchs are distasteful to predators or even poisonous to eat, which allows many species to wander around coral reefs openly during the day.
Many members of the Discodorididae family have flattened backs with numerous coloured tubercles (bumps), similar to Wart Slugs, and a wide mantle skirt. The larger and brighter tubercles (bumps) are often located along the edge of several ridges which run along the back of the nudibranch.
Facelinidae Nudibranchs are colourful aeolid nudibranchs. 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'.