Nudibranchs are sea slugs who belong in the class Gastropoda and order Opisthobranchia. Nudibranchs are known for their camouflage and ability to remain unseen for so long. Another thing they are know for is how they breathe through their gills on top of their bodies. Scientists estimate that they've identified only half of all nudibranch species, and even the known ones are hard to find. Scientists say they have identified only 30,000 different kinds of nudibranchs, so they still have a lot to go. Most live no more than a year and then disappear without a trace, their boneless, shell-less bodies leaving no record of their brief, spectacular lives. Nudibranch's poisonous chemicals are even today helping us cure diseases. They only live for no more than a couple of days, and it is hard to differentiate between the kind of nudibranchs. They are no larger that a teapot, so it is hard to see them.
Nudibranchs do not have a mantle cavity and have bilateral symmetry. They are unlike most gastropods in this way because they have gone through secondary detorsion. The adults vary in size from 20 to 600 mm., and do not have a shell(operculum). Nudibranchs breathe through a branchial plume of bushy extremities on their back, rather than using gills, so therefore the name nudibranch, or naked gills ,suits them finely. Nudibranchs have head tentacles called caphalic tentacles, which are sensitive to touch, taste, and smell. Rhinophores detect odors and are club-shaped. Generally oblong in shape, nudibranchs can be thick or flattened, long or short, ornately colored or bland to match their surroundings. Some kinds of nudibranchs have many finger-like structures on their backs called cerata, which function for gas exchange and often defense against predators. Nudibranchs are blind to the colors they portray, and their little eyes can barely discern between light and dark. Chemical signals help them locate what they are looking for. Scientists today are isolating chemicals that may help hurting heart, bone, and brain. A sea hare (cousin to the nudibranch) recently offered up a cancer-fighting compound that made it into clinical trials.
Nudibranchs are simultaneous hermaphrodites, and can mate with any other older member of their species. They have certain chemicals that help them find food and other things like each other. Nudibranchs have a set of reproductive organs for both genders, but they can rarely fertilize themselves. Their lifespan varies widely, with some living less than a month, and others living up to one year. Nudibranchs usually deposit their eggs within a gelatinous spiral or something else depending on the species. They can also lay up to two million eggs depending on the species. Sometimes if two nudibranchs meet and they are of different species, a fight could break out. The fight usually ends up with one nudibranch eating the other one. To mate two nudibranchs come together side by side and pass sperm sacks through a tube on the right behind the head. Copulation may take seconds or a whole day, depending on the species. Both then go their own way and lay 1-6 egg masses in an anti-clockwise spiral, which may contain many eggs. Hermaphrodism gives these animals a survival advantage in that the mature animals can fertilize and produce eggs.The sperm is stored until the eggs develop, when mating occurs. Egg masses, also known as spawn, can contain millions of mucus sheathed egg capsules attached to the spiral varying size, shape and color. Chemical defence is used to protect the spawn against attacking predators. Nudibranchs take no part in the rearing of their young. They do this because they lay so many eggs that a good percentage will still survive even if most are eaten or killed early in growth.After mating, nudibranchs lay their egg masses either on or near the organism that they eat. Egg development can take between 5 and 50 days, and is influenced by temperature. Warmer waters generally result in a shorter embryonic period. Usually the eggs develop first into a larval form called a veliger, which drifts in the ocean currents as plankton. Specific environmental conditions trigger the larvae to settle and metamorphose into the adult form. This larval dispersal is important in the successful exploitation of new areas, since adult nudibranchs move slowly and cannot travel very long distances.
Nudibranchs live on the bottom of the ocean so they can be called benthic organisms. They can be found crawling along the bottom over seaweeds, rocks, sponges and other substances found on the bottom. They can be found anywhere from the lower intertidal zone to depths of up to 700 m. They can be found all over the world like in the tropics or even Antarctica. They can also be kept in reef aquariums, but most are short lives since many people don't understand how to take care of them or what they need to survive. Warm and shallow waters are said to contain the biggest number of different nudibranch species. They even thrive by huge billowing deep-sea vents, and small tide pools. Nudibranchs are carnivorous, and eat a wide variety of sea life and creatures. Some examples are sponges,algae, hydroids, bryozoans, tunicates, barnacles, and sometimes even anemones. Some nudibranchs are cannibals and will eat each other. To identify their prey the nudibranchs will use their two sensitive tentacles called rhinophores that are located on top of their head. One method of capturing prey to eat is poisoning the prey. They use the hydroid's nematocysts(stinging cells) and line their dorsal walls with them. Then when prey of food comes along, they brush up against them and paralyze them. Another way is more of a natural way. They use their body's camouflage and hide until the prey is right by them and then surprise them and use their poison to capture them. They are also eaten by many things. Fish and larger sea creatures eat them for snacks, but they aren't eaten all that much. Their camouflage and stinging cells help to keep predators away. Certain fish, sea spiders, turtles, sea stars, and a few crabs though will brave the stinging cells and eat the nudibranchs. Some people consume them as well, after removing the toxic organs. Chileans and islanders off Russia and Alaska roast or boil sea slugs or eat them raw. (Photographer David Doubilet from National Geographic likened the experience to "chewing an eraser.")
Camouflage. Their anatomy enables them to resemble the texture and color of the surrounding plants near them. Some of the nudibranch's colors convey a message. They show that this nudibranch has this poison or gas and to stay away from it. Contrasting pigments make them highly visible against a reef's greens and browns, and this is a visual alarm that turns predators wary. Some predators quickly learn to avoid the color patterns that announce uneatable flesh. Animals able to mimic the danger-warning designs, including nontoxic nudibranchs and other invertebrates like flatworms, are similarly left alone. Pigments matching sponges and other edible substances on which they linger can make even the biggest slug varieties disappear where they lie. Many nudibranchs are hidden to divers, and you have to look very hard to find them. Some of them you can't miss because of their bright colors and garish designs. An easy way to see nudibranchs is to look for their egg masses at low tide, and the parents are probably close by. A nudibranch's size is comparative to that of a tea cup, so it isn't surprising if you don't see any while diving. One other defense they have besides camouflage and toxins is by contracting their muscles and swimming a short distance a way.
White Atlantic Cadlina
- Nudibranch by National Geographic Society
- Nudibranch by Aquarium Community
- Nudibranchs by OceanLink
- Living Color: Toxic nudibranchs—soft, seagoing slugs—produce a brilliant defense By Jennifer S. Holland. National Geographic. June 2008.