Scott Bennett

Nembrotha chamberlaini This recently ecology (1997) described species has a very distinctive colour pattern. The rhinopores are bright red

By Michael Arvedlund S cott B ennett annae. This is another of the Chromodoris quadricolour Why are they so colourful? colour group of species characterised by black longitudinal lines, bluish backgrounds and orange borders

Nudibranchs have N onoy T an Naked beauties nude gills. Therefore Most divers have seen them. Weird-looking Nudibranchs are found in all of the scientific Latin the seven seas, from the tropics name “Nudi” (nude) crawling creatures with odd shapes, an- to the polar regions. More than “branchs”. LEFT: tennae and amorphous bodies and 3000 species are known, and new Chromodoris Willani draped in pychedelic colours. We are species are being discovered and not talking about aliens from outer described at regular intervals. The word “” comes from space but nudibranchs. But why the Latin nudus, naked, and the do they have to look so weird? Greek brankhia, gills, and in sever- al languages their name translates Photos by Scott Bennett into “naked snails”. and Nonoy Tan Naked indeed, and clearly ex- Text by Michael Arvedlund posed as such. How do they man- and Peter Symes age to survive in a brutal world full of hungry predators? Chemical defences Without a protective shell, nudi- branchs, and other sea , had to develop a number of other defensive mechanisms against Warning colouration. Many . These include cryptic species with bright colour colouration, or camouflage, and patterns are full of distasteful behavioural modifications, such chemicals. Others with sting- as only being active at night. ing cells or toxic glands have But probably the most significant brightly coloured tips. This spe- development has been the use cis is a Flabellina exoptata S cott B ennett 64 X-RAY MAG : 22 : 2008 EDITORIAL FEATURES TRAVEL NEWS EQUIPMENT BOOKS SCIENCE & ECOLOGY EDUCATION PROFILES PORTFOLIO CLASSIFIED Scott Bennett

Many opisthobranchs Yellow and All different In one nudibranch family, the are mainly active at black. Classic night when predators Usually, each species has very warning col- , the colour pat- are asleep or can- specialised food requirements, ouration dis- terns of many species are spec- not see them. Others and often its defensive molecules played by a tacular and obvious. Research in are able to swim for are also unique and differ from Sagami Bay recent years has shown that these short periods when even closely related species. have specialised glands in disturbed, and so In particular, terpenoid com- their that contain poison- escape predators. pounds, which are derived from ous and distasteful chemicals from N onoy T an LEFT: Chromodoris , are concentrated their food. It is thought willani. This spe- around the mantle border and that by linking bright col- cies is one in the mucous secretions of the our to bad tastes, these of a group of similarly mantle. At their natural concen- nudibranchs can teach coloured trations these chemicals deter fish and other potential species with crabs and reef fishes from preying predators to leave them a bluish white on the . alone. or translucent In a development of white background Why all the colours? this, we often find geo- colour and dark blue Many animals, which are very graphic areas where or black longitudinal distasteful or poisonous to eat, groups of unrelated stripes have bright colour patterns. The chromodorids have bright colours are considered to evolved very similar be a message to potential preda- colour patterns, so tors warning them to stay away. that they share the We call such warning colouration load of teaching fish to Aposematic colouration. leave the colour pattern Egg mass from a Spanish Dancer alone. One example of this Many opisthobranch egg masses form a spiral ribbon, and most of mimicry in southeastern Australia these spiral in an counter-clockwise (sinistral) direction from the centre. However some such as Melibe australis and Melibe engeli seem to be are a group of about ten red dextral, coiling clockwise from the centre. There is some discussion in the spotted species, some of which scientific community as to whether spiraling tends to be counter-clock- are very difficult to tell apart. Most of chemicals to make them wise in the northern hemisphere and clockwise in the south- chromodorids have these posionous, or at least extremely ern hemisphere. To complicate the matter, some mantle glands. ■ distasteful, to potential preda- species start the egg spiral from the outside, tors. In fact, Opisthobranchs (the whereas the majority start from subclass that nudibranchs belong the centre, in which case, the to) have become subjects for re- spiral will be made turning search by marine products chem- the other way. ists who are gradually uncover- ing just how widespread and in what complex ways chemicals are used by sea slugs. Many store these chemicals in special glands in their skin. What has caught the attention of chemists and physiologists are the many different pathways the molecules are produced. In some cases, these compounds are

absorbed from ingested prey and N onoy T an stored unaltered by the opistho- branch, and in other cases, the compounds undergo some modifications. They may also be produced entirely by the opistho- branch itself. Spanish Dancer 65 X-RAY MAG : 22 : 2008 EDITORIAL FEATURES TRAVEL NEWS EQUIPMENT BOOKS SCIENCE & ECOLOGY EDUCATION PROFILES PORTFOLIO CLASSIFIED Scott Bennett Scott Bennett

Discodoris boholiensis. This species is characterised by the nar- row visceral hump, which forms a narrow median ridge from the rhino- Millers phores to the gills, and Nembrotha, wide mantle skirt Nembrotha milleri. One wide- spread method of defence is tropod groups to hide from such as the predators by having a col- sea slugs includ- our, shape ing the colorful & Trivia and/or texture , and A nudibranch is a that matches other hetero- member of one their food or branchs such as suborder of soft-bod- background the , ied, shell-less marine opistho- environ- the sea butter- branch gastropod mollusks, ment. flies, the sea angels, which are noted for their often Grey- other and the often rather extraordinary colors and striking green to kinds of large sea hares. The forms. The suborder Nudibranchia dark green sea slugs word ‘’ is also is the largest suborder of het- body with belonging to sometimes loosely applied erobranchs, with more than 3,000 blackish several taxonomic to the only very distantly related, described species. Nudibranchs longitudinal groups that are not very closely pelagic, caenogastropods within are often casually called “sea wrinkles down related to nudibranchs. A fair the superfamily Carinarioidea, and slugs”, a non-scientific term that the body. There number of these other sea slugs may also be casually used for has led some people to assume are three basal gill are colorful, and thus, even more the even more distantly relat- that every sea slug is a nudibranch. stalks which split into five easily confused with nudibranchs. ed pulmonate sea slugs, However, while it is true that nudi- branching gills Other marine shell-less gastropods the . (From branchs are very numerous in or “sea slug” groups include addi- Wikipedia). ■ terms of species, and are often tional het- erobranch very attractive, there are numerous shell-less gas-

Chemical defence. The skin of many opisthobranchs con- tains distasteful and sometimes toxic chemicals S cott B ennett N onoy T an atromarginata. Although this is the most com- mon species of the group, there are a number of almost identically coloured species dif- ficult to separate from G. atromarginata

66 X-RAY MAG : 22 : 2008 EDITORIAL FEATURES TRAVEL NEWS EQUIPMENT BOOKS SCIENCE & ECOLOGY EDUCATION PROFILES PORTFOLIO CLASSIFIED Not new but Good to know: New nudibranch books still very handy Aeolid Neville Coleman’s new Nudibranchs Encyclopedia – a review and how it compares to the new Debelius and Kuiter Nudibranchs of the World. the Debelius/Kuiter book focuses The Aeolid cnidosac is one of the on the family Chromodoridae. It is most remarkable examples of recy- Tim Hochgrebe, Underwater Australasia amazing to see the regional col- cling in the kingdom. These our variations in some species. animals feed on cnidarians (sea x 235 mm), and for images to this book. It is great to In summary, as a big nudi lover, anemones, corals, hydroids, , etc.) and are capable retaining at nudibranch fans, this see how many people share the you will obviously have to have least some of the cniadiran’s sting- book will still fit into passion and enjoy finding new both books. The Debelius/Kuiter ing cells (nematocysts) in a func- their travel case. and previously unseen species book really made me want to tional state, so that they are able The first 30 or so and behaviour. By accepting go and spend more time diving to reuse them in their own defence. pages is dedicated other people’s contributions, the outside the Asia and Indo-Pacific The atlanticus (below) is an to nudibranch biol- scope of the book has certainly region, as there are so many example of a nudibranch ogy, which makes widened, and the quality of the beautiful nudibranchs I have yet that can severely sting this book much more imagery has improved, as there to discover. In terms of usefulness, humans. than just a reference were more images to chose from. I prefer Neville’s book—there are book to identify that Over 3000 images are con- more images, it is focused on my strange new nudi- tained in this work, which makes favorite region, and will definitely branch you found on it the most comprehensive pub- become the first book to open your last dive. He talks lication on nudibranchs in the when I see a new nudibranch, or T aro T aylor about the different world. And since it focuses solely when people submit images to habitats where nudi- on Asia and Indo-Pacific Sea sea the Underwater Australasia photo branchs are found slugs, it is clear that this book is to galleries and ask questions about The book should really be titled and also how to find become ‘the bible’ for slug lovers the identity of their find. Sea Slug Biology ... I also find the them. He explains diving this region of the planet. To purchase your own copy of term behaviour a bit misleading. It how they see, smell, Another new book on nudi- these books, have a look at the is, however, a great book. hear, taste and feel branchs is Helmut Debelius and book section at the link below: Nudibranchs are among the most and all with beautiful Rudi Kuiter’s title Nudibranchs of underwater bookshop. ■ beautiful creatures on the reef, Cnidarians, or photographs to illus- the World. This book is much with colors and shapes that daz- coelenterates, trate each fact. larger in size (210 x 280 mm), zle and delight. Unlike fish that have a wide range There are some and therefore quite a bit may disappear before our eyes of nematocysts, some in a flash, the showy nudibranch excellent sections on heavier. Pages within the of which are used for poisoning glides slowly along the substrate, prey, some for catching by harpoon- nudibranch behav- book have excellent print allowing us the time to savor this shaped barbs, others for entrapping iour, including tailing quality and stunning pho- extraordinary sight. With their shell- with sticky secretions or entangling of individuals, burrow- tograpy. Nudibranchs of less unprotected bodies, how coils. The three nematocysts in the The long awaited Nudibranchs ing and mantle flapping behav- the World feels more like a do they survive in seas filled with cnidosac photo above are barbed Encyclopedia - Catalogue of iour, and of course, nudibranch coffee table book of nudi- hungry mouths? How do these nematocysts. When they are trig- Asia and Indo-Pacific Sea Slugs sex and defence. branchs than a reference sightless creatures navigate the gered, the spiral thread, which is by Neville Coleman has finally In his typical emotional style book, reefs to find food and mates? easily seen in the photo, uncoils as arrived and what an encyclo- of writing, Coleman manages to In contrast to Colemans What and how do they eat? How a long thread to attach the barb to pedia it is! draw the reader into the passion book, which includes ophis- do they reproduce? What special the cnidarian, or in this case, to the relationships have they devel- and excitement that these critters tobranch (non-nudibranch) cnidosac. oped with other reef inhabitants? Neville Coleman has made the bring to his life. This makes the sea slugs, Nudibranchs of These and many more questions It is now thought that nematocysts excellent decision to publish this book much less ‘dry’ than many the World only covers true are answered in this informative reach a state of physical but not massive book as a hardcover, of the books written by scientific nudibranchs and sorts them and lavishly illustrated book. You physiological maturity in the cnidar- and with its over 400 pages, it ‘purists’. in a more evolutionary or will never look at nudibranchs the ian. Usually, after some time, they really needs to be. The hardcover Another difference to scientific manner. It has an same way again. ■ then become part of the cnidarian’s functional armoury. It is thought that makes the book more profes- Coleman’s previous nudibranch introductory section to each the nematocysts, which are captured sional, and naturally, it will last publications is the fact that he family that highlights the Soft cover: 177 pages and able to be used by the aeolids, longer in any diver’s library. He still openly invited many nudibranch specific features that dif- Size: 180mm x 250mm are those that are physically mature managed to keep the book quite lovers from around the world ferentiate each family from ISBN: 1-878348-41-8 when eaten, but not yet physiologi- compact in its dimensions (160 to contribute their findings and the others. Over a third of cally mature. ■

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