Discussions
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A LITTLE DIFFERENCE IN DECORATION
 Chromodoris decora is one of those nudibranch species that while found occasionally under rocks intertidally is only rarely seen subtidally. It is a small species with disruptive colouration and is probably often overlooked. Through various reviews the name has changed from Doris decora to Glossodoris decora and is now known as Chromodoris decora.
We all recognize Chromodoris decora by a couple of distinctive features. The mantle has three thin, white, longitudinal lines. The outside white lines continue around the front of the rhinophores and the back of the gills, together forming a loop. The medial white line often forks in front of and around the gills. There are purple spots between the white looping line and the orange border to the mantle. There may also be purple spots inside the looping line and also on the medial white line. The rhinophores and gills are uniformly cream.
Pease first described this slug from Hawaii as Doris decora in 1860 but did not include an illustration. His description however contained the following: “…..a medial whitish longitudinal strip which is bifurcated posteriorly and dotted with purple”.
Berg in 1880 published an illustration of a slug recognizing the name that Pease gave it earlier and which clearly showed the features described.
In 1938 Baba described a similar animal but although it did have a white forked medial line, that line did not bear the purple spots. He named his animal Glossodoris setoenis. Later, in 1953, Baba suggested that his animal should now be considered a synonym of Pease’s decora. Gosliner, Behrens & Valdes, (a) list this type as Chromodoris setoenis (Baba, 1938) with the notation: “Additional work is necessary to determine whether these are color variations or distinct species.” Marshall & Willan, (b) are of the opinion that it is a synonym, as is Rudman, (c).
All of the specimens of Chromodoris decora that we have found to date in southern Queensland waters have been of the “Baba variety”, that is, without purple spots on the white medial bifurcated line. This type appears to have a wider distribution and therefore seems to be much more common than the type originally described by Pease. Pease’s type definitely has a more “easterly” Pacific distribution e.g. Hawaii, Guam, Tonga and New Caledonia.
Read more:
(a) Gosliner, Behrens & Valdes, Indo-pacific Nudibranchs & Sea Slugs, 2008, p. 224
(b) Marshall & Willan, Nudibranchs of Heron Island, 1999, pp. 93-94
(c) Rudman, www.seaslugforum.net, Message # 20717, 2007
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MAKING SENSE OF SIMILAR VARIETY
 When you have set yourself a goal to find all the species of sea slugs in a certain area or region there are certain methods by which the search can be continually driven. One of those methods is to set other goals, such as a species count that must forever be driven upwards. Unfortunately by focusing purely on increasing that count we can sometimes lose sight of what we are really trying to achieve.
Just the other day we were trying to convince ourselves that some differences in mantle colouration and pattern were sufficient to call a specimen a different species. Some further research on similar looking species only served to confuse us. The particular group in question are those in the Chromodoris tinctoria (top photo) and Chromodoris reticulata (bottom photo) sphere.
In reviewing those species on all the websites and in all the books available to us as well as images forwarded to us by like-minded colleagues, we were overwhelmed by a virtual constellation of variety, but similar variety we might add. This description might be an oxymoron but it serves to highlight our dilemma. How to make sense of this?
The Sea Slug Forum takes the view that they are all but variants of just one species, a continuum of variety and similarity all linked by virtue that “….the species differences suggested by different colour patterns is not supported by internal anatomy.” The Forum further suggests that the differences are mainly associated with colour and pattern at the mantle edge. As the earliest name for any of the described species in this group was Doris tinctoria Ruppell & Leuckart, 1830, they are all grouped on the Forum under Chromodoris tinctoria (Ruppell & Leuckart, 1830).
Gosliner, Behrens & Valdes in their recent book Indo-Pacific Nudibranchs & Sea Slugs take the completely opposite and extreme view by listing members of this group as 11 distinct species on the basis of the colour patterns in photographs. They justify this position with the assertion that: “….there are consistent differences between specimens from different geographical localities.”
These are obviously the two extreme positions in this debate.
Our colleague Richard Willan on the other hand (Nudipixel & personal correspondence) leans towards the conservative end of the spectrum, believing there is no evidence to warrant calling them all different species, and commenting: “Whatever the species boundaries are, and whatever the name(s), it is clear the species within this group are highly variable.” He does however divide them into two broad groupings on the basis of observable external anatomical features namely, the number of gills and the size of the adult, as follows.
Chromodoris tinctoria (Ruppell & Leuckart, 1830):
Small when adult and less than 8 gills.
Chromodoris cf. reticulata (Quoy & Gaimard, 1832):
Large when adult and more than 12 gills.
Richard’s use of reticulata is explained thus: “…it was clear the name C. reticulata was becoming prevalent, through ignorance, on lots of internet sites. This is because the name can be matched to a reasonably good and recognisable drawing by the French scientists Quoy & Gaimard in 1832.” and further “So…I used reticulata, together with the cautionary “cf.” to indicate there was uncertainty that the southern Qld species matched the true C. reticulata (whatever it might be), in Undersea Jewels.”
We find this latter argument convincing. Our mindset has now been changed not only to finding all of the species, but also all of the many variations to all those species, which can be just as rewarding even though it does not increase our species count. It is human nature to try to understand and make organisation out of perceived chaos. One of the tried and tested methods is to classify everything according to an accepted code. However as Richard responded to one of my identification questions: “Essentially your question/observation strikes at the heart of all opisthobranch taxonomy. What are the limits of a species? That question still remains subjective, even though the answers might be morphologically based or (more and more nowadays) genetics based.”
Where then does this leave the differing opinions on this group? Richard Willan’s summing up is thus: “All I can do at this time is repeat their (Gosliner et al) words: ‘The entire group is in need of a major review.’”
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Spurilla neapolitana
Spurilla neapolitana is a nudibranch species now showing a wide-range of distribution. It is now considered to be a tramp species in many parts of the world with the assistance of human activities most likely through the action of commercial shipping.
There is an excellent and elucidating article written by Richard Willan and published in the Malacological Society of Australasia’s Newsletter (No. 130 October 2006) from which the following excerpts and information are taken.
“Nudibranchs are especially good at hitching rides on ships’ hulls; one could describe them as long-distance back-packers. Their rapid life cycles, high reproductive output, physiological adaptability and opportunistic diets, have preadapted them to travel widely round the globe thanks to mankind’s sea voyages.”
“Spurilla neapolitana was first described in 1823 from Naples in southern Italy. Its spread around the world over the last 50 years has been truly meteoric, with records from the tropical western Atlantic, California, tropical eastern Pacific, Hawaii, Japan and Hong Kong.”
Our colleague, Denis Riek of Brunswick Heads, made the first Australian find in May of 2005 and it has been reported a number of times since from various localities along the New South Wales coast. This intertidal find at Caloundra is a new record for Queensland.
The sudden appearance of Spurilla neapolitana in many parts of the world has workers in this field confusing it with local species and even recording it as a new species.
The distinguishing characteristics, especially pronounced in the adult, are the lamellate rhinophores, the long and slender cerata coiled near the tip, and the white spots all over the body and cerata. The diet of Spurilla neapolitana is sea anemones, and a wide variety of sea anemones at that, with the type and colour of those consumed contributing to the background colour of the slug’s body, which can be brown, pink or red.
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How to tell if it is a Janolus
Our species list now contains two Janolus.
With a profusion of cerata on their dorsum Janolus could easily be mistaken for an aeolid, but in belonging to the Zephyrinidae family the Janolus are armininans not aeolids. Although having an aeolid-like form the most readily observable feature of distinction is that in the Janolus the cerata continue uninterrupted around the anterior margin of the head, a feature no aeolid possesses (refer pic above, from The Collection).
A further helpful attribute of distinction is the location of the anal papilla. In Janolus it is located on the dorsal midline posteriorly (see Erik Schlogl's message at www.seaslugforum.net/message/19798), whereas in the aeolids it opens to the right anterior quarter usually on the side. Whilst the rhinophores are non-retractile in both the Janolus and the aeolids, the Janolus possess a distinctive ridge between the rhinophores at their bases. This longitudinal ridge is called a caruncle and its purpose is unknown, although some have variously suggested it performs a sensory or defensive purpose.
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WHAT’S A FREAK?
(COLOUR FORMS AND DISTRIBUTION)
 It is to be expected that the more you dive the more unusual sights you will see. Then again you might think that the odd or unusual observation may become commonplace or at least a pattern develops that explains the atypical.
We had a pleasant dive on the HMAS Brisbane wreck last week and apart from some nice finds a couple of unusual things came to our attention.
The first concerns Tambja tenuilineata a small polycerid that we regularly find right across the Gneering Shoals and at Old Woman Island, grazing upon bryozoans. It is recognized by its green body colour with numerous narrow black longitudinal lines, and green rhinophores and gills tipped in purple. This is how it always presents to us - or so we thought. On this dive we found a plain specimen without the black stripes but with wrinkles or furrows instead. A search of our records revealed that we had found this colour form once previously - approx 12 months ago - also on the Brisbane. So far therefore - no stripes only on the Brisbane but with stripes everywhere else. Perhaps we will allow a few hundred more dives to pass before we attempt to draw any wild conclusions from these observations.
The second is with regard to Chromodoris splendida, a very common almost ubiquitous species here. All divers are familiar with its “strawberries and cream” appearance, with the red colouration in our region presenting as a single or group of large blotches on the dorsum. Over the past 7 years, of the many hundreds sighted we have only once found it without any of the red blotches. This was at Old Woman Island. Last week on the Brisbane we saw many of the usual sort but also two specimens without the red blotches. When first observed without these red blotches their appearance is a little disconcerting and one can’t at first establish what is wrong about it. Check the gills, check the rhinophores, and check the band on the edge of mantle and foot. All present and correct. Another oddity recorded.
Finding an oddity for the second time makes it less of a freak to be ignored and more of an acceptable, recordable variation.
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Latest News
25 August 2010
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WHERE, WHAT AND WHEN?
For seven and a half years now we have been seriously searching for and recording every species of Opisthobranch in our survey area. Over that time as we gained experience and skills we collected and added further information about these creatures to our records. We have information about the families to which they belong, information about their natural history, i.e. mating, spawning, feeding and various external anatomical features. Sometimes we had discussions between ourselves about which site was the most productive or which species was the most frequently found etc. Often these “discussions” led to differences of opinion and disagreements arose.
Exactly twelve months ago it was decided to develop a database of our finds for each trip recording the species found at each site. We felt that the six and a half years we had spent searching up until then had given us sufficient experience to be confident that we would know where, how and what to look for in order to find most of the creatures in the area we were searching. By putting the information we have recorded over the past year into a database it has allowed us to produce some interesting facts and statistics.
- Most productive site:
Shellacey Reef, Gneering Shoals with 98 different species from 10 trips comprising 19 dives with 2 searchers on each dive.
- Second most productive site:
Flinders Reef (western side) with 75 different species from 11 trips comprising 18 dives.
- Concerning where we find most species new to our list:
Flinders Reef (western side) has produced 16 new species and Shellacey Reef 11 new species.
- The most productive trip:
Trench, Gneering Shoals on 21/11/09 when we recorded 37 different species.
The information we enter into the database is taken from our Blogger on the website. If you visit the Blogger you will see the list of species found on each trip with the date and site recorded. Pics taken that day of some of the species are also posted there as well as underwater views of the site.
No more arguments anymore - we just interrogate the database.
9 July 2010
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LATEST UPGRADE
 David has also decided to keep up with the team and upgrade his underwater camera equipment.
He has had a Nikon D300 camera for some time now and elected to source a housing for that. There are a number of manufacturers offering housings for this camera body but David chose to stay with Subal. During the seven years he used a Subal housing at least weekly for his Nikon Coolpix 5000, he experienced absolutely no problems. As well as the robust build and features of the Subal design he favours their style of sealing clamps and the handgrip ergonomics.
Together with the housing, he purchased ports to suit his Nikkor 60 mm and 105 mm micro lenses and a port extension ring to accommodate the supplementary dioptres he likes for macro work. The set-up was rounded out with the addition of the 45 degree full frame viewfinder and Inon LED focus light. The system will accept his current pair of Inon Z220 strobes which also haven’t missed a beat in seven years of abuse.
So what benefits can he expect from this upgrade?
Lenses: Improved optical quality, larger diameter lenses = more light, greater range of apertures down to f32 and therefore more depth of field
Camera: Larger sensor, more pixels, bigger pixels, longer battery life, larger review screen, more reliable autofocus and active focus points
The proof of all this will no doubt have to be seen in the results, but what guy doesn’t want to play with new tech stuff anyway. The new system has a hard act to follow which is why he isn’t throwing his old system away, just yet.
8 July 2010
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THE SHAPE OF THINGS
We think a common chord will be struck with all our fellow fanatical sea slug brethren when we say that we often discern sea slug shapes in the most unlikely objects and at the most unexpected times.
 Take a look at the pic left. This little beauty was spotted during a walk along the foreshore by one of us. It first caught the eye, then the attention, the heart misses a beat and a short sharp breath is taken. The mind instantly says Sacoglossan - Thuridilla! Then reality and common sense prevail and override the emotional turmoil. It’s picked up and examined and the incredible shape that momentarily deceived the mind is marvelled at. So to is the way in which the mind works. The imprinting created by hours and hours of scouring the depths in the hope of finding just such shapes is not easily turned off. It’s not a slug, but the whimsical situation it created brings a moment of delight and recognition that the methods we use to uncover them have an effect upon and spill over into our everyday life. (Psychologists would probably give it a name like pattern recognition.)
We collected this “specimen” and kept it as a reminder of our obsession with the single-minded search for particular shapes beneath the waves because it is the shape of things, among the myriad of other shapes, that most often lead us to the objects of our desire.
(Note: This “specimen” is an unusual leaf shape of a Norfolk Pine.)
18 March 2010
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CAMERA UPGRADE
 After seven years of faithful, meritorious service and 70,000 images Gary’s Nikon Coolpix 5000 in its Subal housing has gone into semi-retirement.
As technology rolls on and camera features are developed and enhanced it is just a matter of waiting until the right combination of these features are rolled into a camera that is suitable for underwater use, especially in macro mode. It’s not that there is anything wrong with the old camera it’s just that the improved features make the taking of the photos easier and those photos are of a better quality with additional information, lending themselves more readily to correction and enlargement/cropping.
Gary has invested in a Canon G10 and Ikelite housing, but is utilizing one of his original Inon Z220 strobes. The G10 has 14.7 mega pixels on a 1/1.7” size sensor, 5 x optical zoom, and a large and very bright 3’’ screen. For nearly all of his sea slug photos he also uses a slip-on, wet close-up lens for optical magnification.
He is particularly impressed with the viewing screen which makes subject composition and review a delight, and also with the size of the image that this camera produces. While the G10 is not the latest from Canon it is definitely a better camera for our purpose than the more recent G11.
We salute you, Coolpix 5000, for a job well done. We welcome you, G10, for the improvement you promise. Seven years of underwater service are big shoes to fill.
26 February 2010
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STARS AND STRIPES
Our trip to Flinders Reef off Cape Moreton last Tuesday has proved more rewarding than we initially thought. Apart from fabulous visibility and glassy conditions, species number 417 for our list was found by David Hill, a colleague who sometimes dives with us and has excellent eyes for our main game.
Our first thoughts were that we had found Cyerce nigra again, feeding on the green Turtle Grass weed, Chlorodesmis fastigiata. Not so, we were informed by our colleague Richard Willan, whose own sharp eyes and depth of knowledge quickly corrected us. It was Cyerce nigricans.
The obvious difference (to us now) is in the markings on their leaf-shaped cerata. Richard pointed this out to us in commenting on the photo “The Cyerce has spots on the front face of the cerata instead of concentric lines - that makes it C. nigricans.” and “I had always assumed they were colour forms, but then Clay Carlson showed there were consistent differences in the radula which matched the differences in the colour pattern, so they are regarded as two separate spp. now.”
VISIT FROM RESEARCHER
 The team at nudibranch.com.au were pleased to be joined last week by Dr Nerida Wilson from Scripps Institute of Oceanography, UCSD in California, who is visiting her native country to attend and present at the Molluscs 2009 conference in Brisbane next week.
Nerida is undertaking some broad molluscan research and was very interested to learn that we had been finding them at Bulwer, Moreton Island and at Woody Point, Redcliffe Peninsula. She joined us for a couple of sieving sessions at Woody Point and also for 2 long dives from aboard Mischief over at Bulwer last Saturday. In fact it was Nerida who happened to find for us our 405th species, the burrowing gymnodorid, Gymnodoris sp. 5, whilst sieving at Woody Point. (See news article below)
She filled us in a little on what is happening with molluscan research, answered all of our questions, serious and silly, and was otherwise excellent company. We are certainly wiser and more informed for the visit.
14 November 2009
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A BURROWING GYMNODORID!
 This unusual species of gymnodorid was found whilst sieving the dark and muddy silt on the intertidal flats at Woody Point. The water depth was approx 300 mm at low tide.
The general body shape is that of a typical gymnodoris; soft, elongate and tapering to a tail. The mantle is much reduced to a skirt around the anterior end. The body is transparent with the viscera clearly visible and is covered with numerous very fine red spots.
There are though three extraordinary attributes immediately apparent that mark this species apart from the typical gymnodorid:
- The gills are reduced to a single tapering and undivided translucent triangle which is immediately preceded by a slightly raised white ridge curving protectively in an arc.
- The rhinophores are fused and located in a pocket.
- Instead of crawling at speed around the container hunting for prey it spends its entire time going through contortions in attempts to burrow.
These physical features appear to be adaptations for burrowing and, together with its behaviour, point to an infaunal lifestyle. It obviously hunts for prey within the substrate.
12 November 2009
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THE DAILY TALLY
We are now publishing a species list of all the sea slugs found upon each dive trip. The digital camera with its huge memory capacity has made this possible as we can take a quick pic of each species found. Those pics may not win a prize for composition or exposure but they are a ready reference to corroborate our recollection of sightings after the trip.
If you click upon NUDIBRANCH CENTRAL BLOGGER (in the navigation barat the top left of each page) it will open up our blog page. Following each trip we will list here all the species found at that site on that date. There is even a facility there for you to post a comment which can include any questions you might have.
It is our intention, sometime in the near future, that this information about species, sites and dates will be entered into a database allowing us to generate statistics, for example: Where has a certain species been found? What is its frequency of occurrence? What species have been found at a particular site? Which species are seasonal?
The ultimate extension to that is the desire to make access to the database also available to readers allowing them to search for this information themselves from our site. But first all the ground work has to done to collect the data in the first place. At first we regretted that we had not done this from the beginning of our quest over 6 years ago which would have provide us with much more data, however we now believe that in the early days our hunting/observational skills left a lot to be desired. With these skills honed over that period we are now more likely to produce a more accurate daily tally of the opisthobranchs that are there to be found. (Slugs are where you find them.)
29 October 2009
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BUILDING CARICATURE
Mimicry in the animal and plant world is a most interesting area of study because it raises so many questions about relationships between quite diverse levels of life.
I can remember being told, when complaining about some one copying me or what I was doing, to not worry about it and that: imitation is the greatest form of flattery. Being very young at the time I considered these people to be a much lower form of life anyway.
In the Sea Slug world it probably has more to do with survival by appearance than anything else.
Zoologists talk about Batesian and Mullerian types of mimicry but we believe we have stumbled upon a 3rd type. We think we can demonstrate this 3rd type of relationship between some Sea Slugs and inanimate “objects” although these “objects” are far more famous for their animation.
 Look, for example, at this picture of a species of Atys. There is without doubt a definite similarity between it, when viewed from the anterior end, and a certain type of feline. Our research has pinpointed the feline in question to be without the shadow of a doubt as none other than 'Felix the Cat'. Note the extreme similarity with the ears of each, and don’t be put off by other unimportant anatomical differences.
We are calling this new type of relationship Cartoonian mimicry. We have not been able to establish definitively as yet just what either gains from this but further research will no doubt supply the answer. Early interpretations of our data lead us to believe that Felix gains the cute look which has made him so famous the world over whilst Atys can now claim some celebrity status even though leading the quiet infaunal lifestyle. Cartoonian mimicry requires a different mindset to comprehend fully. Whilst recognition is an important aspect it is not about survival but about fame. It’s not about deception but about adulation and entertainment! Yes, this opens up whole new fields of study for those with the perception and idle hours to fill, to lead the way.
As a mark of recognition we are conferring a common name upon this species. Until such time as it is formally described by taxonomists we are referring to it not only as Atys sp. 4 but also Felix the Atys.
(in gaudio absurdum)
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