When we look at some creatures, we get a feeling that the Creator surely was in a playful mood and used all the bright colours and shapes to produce these fascinating toys. Some such creatures are — Nudibranchs.
These belong to Phyllum Mollusca and Class Gastropoda. Nudibranchs are a part of sea-slug family and exhibit amazing colours, shapes and patterns. The variety of colours, patterns is so vast that one species is not like any other.
These soft bodies molluscs are found in the shallow waters of the tropics and also in Southern ocean. At present around 3,000 species of Nudibranchs are scientifically known. They derive their name Nudibranch (NEW-dih-bronk) from Latin nudus, which means naked, and Greek brankhia, which means gills. They have acquired this name because these molluscs shed their shells after larval stage and sport feathery gills on their backs or the posterior parts.
They are found crawling on the sea bed or on some substrate. They possess a flat muscular foot for locomotion. Very few species can either float or swim in the sea.
The size of an adult Nudibranch varies from 4 mm. to 600 mm, some species can also grow up to 30 cm.s. They have very tiny eyes, barely one fourth of a millimetre in diameter. Their eye-sight is not very strong and can only differentiate between light and dark.
Externally they appear to be bilaterally symmetrical.They have tentacles on the head (cephalic tentacles) which help in detecting touch, taste and smell. Some species have finger like appendages called cerata on the back. These appendages can be of various shapes and their functions include breathing, digestion as well as defence (to warn off the predators).
They have got sensitive tentacles, called Rhinophores, on the top of their heads. These can detect odours and thus the Nudibranchs can find their prey. Some species are known to produce sound.
Generally oblong in shape, they are ornately coloured. but some species have drab shades, in order to dissolve in the surroundings. This helps in capturing their prey and also in dodging the predators.
The Nudibranchs derive their colouring from their food. They are carnivores and prey on algae, sponges, anemones, corals, barnacles and also, other nudibranchs. Flamboyantly coloured Nudibranchs are good example of marine aposematism. The word Aposematism means, warning colouration of toxic material. They can store Nematocysts (stinging cells) and also chemical defences from their preys and use it against their predators. Some species can produce their own toxic chemicals. (However, most of them are harmless to humans). Some Nudibranchs produce their own food by photosynthesis, using the chloroplast obtained by eating algae.
The life span of the Nudibranchs varies from a few weeks to about one year. They are Hermaphrodites, which means each slug has reproductive organs of both the sexes (but they cannot fertilise by themselves). Their eggs are spiral or coil shaped. The larvae possess shells up to the time of metamorphosis.
[There are lot more scientific details about anatomical appendages, also various species etc; but I’ve written only about the basic facts, in order to keep the post short.]