The bottom-dwelling, jelly-bodied nudibranch (NEW-dih-bronk) might seem an unlikely canvas for Mother Nature to express her wildest indulgences of color and form. But these shell-less mollusks, part of the sea slug family, bear some of the most fascinating shapes, sumptuous hues, and intricate patterns of any animal on Earth.
There are more than 3,000 known species of nudibranch, and new ones are being identified almost daily. They are found throughout the world's oceans, but are most abundant in shallow, tropical waters. Their scientific name, Nudibranchia, means naked gills, and describes the feathery gills and horns that most wear on their backs.
Generally oblong in shape, nudibranchs can be thick or flattened, long or short, ornately colored or drab to match their surroundings. They can grow as small as 0.25 inches (6 millimeters) or as large as 12 inches (31 centimeters) long.
They are carnivores that slowly ply their range grazing on algae, sponges, anemones, corals, barnacles, and even other nudibranchs. To identify prey, they have two highly sensitive tentacles, called rhinophores, located on top of their heads. Nudibranchs derive their coloring from the food they eat, which helps in camouflage, and some even retain the foul-tasting poisons of their prey and secrete them as a defense against predators.
Nudibranchs are simultaneous hermaphrodites, and can mate with any other mature member of their species. Their lifespan varies widely, with some living less than a month, and others living up to one year.
Nudibranchs live at virtually all depths of salt water, but reach their greatest size and variation in warm, shallow waters.
The body forms of nudibranchs vary enormously, but because they are opisthobranchs, unlike most other gastropods they are bilaterally symmetrical because they have undergone secondary detorsion. Some species have venomous appendages on their sides. These are used to deter predators. Many also have a simple gut and a mouth with a radula.
They lack a mantle cavity.
Solar powered Pteraeolidia ianthina have adapted cerata to contain zooxanthellae which continue to photosynthesize and provide energy to the nudibranch.
Their eyes are simple and able to discern little more than light and dark. The eyes are set into the body, are about a quarter of a millimeter in diameter, and consist of a lens and five photoreceptors.
They vary in adult size from 20 to 600 millimetres (0.79 to 24 in).
The adult form is without a shell or operculum (a bony or horny plate covering the opening of the shell, when the body is withdrawn).
The name nudibranch is appropriate, since the dorids (infraclass Anthobranchia) breathe through a "naked gill shaped" like branchial plumes of bushy extremities on their back, near their tail rather than using gills. By contrast, on the back of the aeolids in the clade Cladobranchia there are brightly colored sets of protruding organs called cerata.
Nudibranchs have cephalic (head) tentacles, which are sensitive to touch, taste, and smell. Club-shaped rhinophores detect odors.
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Nudibranchs, Nudibranch Pictures, Nudibranch Facts