Slugs. They are not that interesting, but underwater, well they are a completely different matter. They are one of the craziest looking things underwater and are known as Nudibranchs. They are a favourite of many divers and underwater photographers, you have may have heard the term "Nudi" banded about, if so this is what they are talking about. But what exactly are they, and what makes them so special to so many divers?
THE GEEKY BIT: The word "nudibranch" comes from the Latin nudus, naked, and the Greek βραγχια, brankhia, gills. Literally, “naked gills” – the gills are external, generally in the appearance of antennae or tails, in order to extract as much oxygen from the surrounding water as possible. Nudibranchs occur in seas worldwide, including both the tropics and Antarctica, and can live at virtually all depths of salt water, from the tidal zone to depths in excess of 2 km, meaning that wherever in the world you are, you can go hunting for these beautiful and tiny critters!
Here is just a bunch our our favourite species from around the world (all photos courtesy of National Geographic - I wish these were our photos):
- 2. One of the more obvious display of the naked gills, on the feathery “horns” covering this Tritonia nudibranch’s back.
- 3. Unknown species (Philippines) – I couldn’t find the species name for this one, but it is a fantastic display of the incredible colours and hues, which they gain from the food that they eat (as well as gaining toxins to protect them from predators).
- 4. A Chromodoris nudibranch, this time from Palau. Another great example of an incredible and vibrant colour scheme. Although nudis range from cold to tropical waters, the most vibrant, colourful and delicate nudibranchs tend to be found in the tropics.
- 5. Nudibranchs are hermaphroditic, carrying both male and female reproductive organs. Mating pairs fertilize one another and lay up to two million eggs in coils, ribbons, or tangled clumps, as this Hypselodoris Nudibranch is doing.
- 6. Nudibranch are almost blind, their tiny eyes discerning little more than light and dark. Instead the animals smell, taste, and feel their world using head-mounted sensory appendages called rhinophores and oral tentacles, which you can see clearly in this photo of a “green-and-orange” nudibranch.
- 7. Nudibranchs are carnivores that slowly ply their range, grazing on algae, sponges, anemones, and corals. Many, like this red-white-and-blue aggressor devouring a sea hare near Bali, Indonesia, will assimilate the toxins and nematocysts (stinging cells) of their victims and use them for their own defense.
- 8. The toxic flesh of nudibranchs like this "sea clown" species is palatable to only a handful of sea creatures, including other nudibranchs. Other predators include certain fish, sea spiders, turtles, sea stars, a few crabs, and occasionally humans.
- 9. Generally oblong in shape, nudibranchs can be thick or flattened, long or short, ornately colored or drab to match their surroundings. Some max out at a quarter of an inch (6 millimeters), while others can reach a foot (30 centimeters) long or more.
- 10. Nudibranchs' unique lives and body chemistry may harbor breakthroughs that could benefit mankind. Scientists are attempting to derive pharmaceuticals from their chemical armory and get clues to learning and memory from their simple nervous systems.
- 11. A Ceratosoma nudibranch in Indonesia's Lembeh Strait hosts an imperial shrimp, who exchanges cleaning duties for a free ride and access to food.
- 12. Nudibranchs' colorful lives are short, lasting less than a month in some cases, and rarely more than a year. Their elusive nature makes them difficult to study, and their boneless, shell-less bodies leave no record of their brief existence.