Studies on Red Sea opisthobranchs

Preparation for a recent presentation given to the Conchological Society (30 January 2010) made me realize that since my last two publications on the Red Sea, several papers have been published and there have been a number of additions and changes to the fauna lists. This has an impact on both the species composition of the Red Sea as well as biogeographical implications. These two topics will be briefly discussed here.

Seaslugs of the Red Sea, the first “complete” work on the Red Sea opisthobranchs is a beautifully illustrated book (not my photos!), based on numerous papers by various scientists who have been working on the fauna for over almost 200 years (Yonow, 2008a). The book covers an introduction to the Red Sea, including physical and biological characteristics, ending with a section on biogeography and endemism. I was very lucky to have found and been able to include the very first chart ever produced of the Red Sea, by Carsten Niebuhr in 1772. He was on the first scientific expedition to the Red Sea, commissioned by the Danish King Frederic Vth, including the famed Peter Forskål. All scientists perished on this expedition except Niebuhr, who succeeded in getting to Yemen and from there to India and back home, with trunks of specimens and manuscripts, notes and drawings. There is then a brief history of opisthobranch research conducted in the Red Sea, illustrating all the ancient engravings dating from the 19th and early 20th centuries of sea slugs, most of them for the first time. Short biographies and portraits of these famous naturalists are also included.

The second part of the introductory chapters covers the biological aspects of opisthobranchs in sections, beginning with taxonomy and biology, followed by summaries of the characters of the different orders, with diagrams illustrating their salient features. The different groups are so varied that many of the functions also vary. I discuss topics such as defence, respiration, reproduction and development, diet and feeding, and locomotion in relation to the different orders.

The large checklist of species is somewhat tedious, but (in theory) it includes every species recorded in the scientific literature from the region, as well as who recorded it, so it is a rather straight-forward affair to double-check identifications when there are nomenclatural changes and changes in taxonomy. The remainder (apart from refs and glossary) and bulk of the book is based on several photographs illustrating each of nearly 200 species, with the text documenting technical information such as size, characteristics, and distribution. It includes many species which were then unidentified but occurred not infrequently (for a sea slug), so there is a fair amount of information available for the species, even though they may not have names. A few of these can now, two years later, be assigned to a specific epithet, and the distributions are a little better known as a result. A number of species had been identified with known Indo-Pacific species, but have since been shown to be endemic Red Sea species. Endemism of opistho-branchs in the Red Sea stands at around 25%! In the final chapter there are photographs of many uncollected and therefore unidentified species, of which five can now be assigned with some confidence to a species, all first records for the Red Sea.

As I was finishing the book, I was also preparing a paper on the same subject, but with a Gulf of Eilat and zoogeographical bias for a conference (Yonow, 2008b). I used the same basic table as in the book, but in this case I omitted the records with their recorders, and instead listed the zoogeographical distribution and endemic status of each species, with colour codes for the regions, and as such they complement each other very well. It is beyond the scope of this article to present a new 6-page list of updated information, but the implications will be discussed, with a few illustrations. A table of new identifications is presented here, for anyone who would like to update their copies.

Slugs of the Red Sea - updated names

The fauna of the Red Sea was first explored in the early 1800’s by several expeditions. With today’s methods of diving and snorkelling on reefs, one wonders how they possibly collected these soft-bodied animals which are mainly subtidal, tucked away amongst coral and rocks, and living on coral reefs. Dredging and grabbing on soft sediments were classic methods, and one must presume similar methodologies were used over reefs, which must have caused some terrible damage. The fact that some of the paintings are beautifully detailed and accurate is certainly a testament to the fact these early scientists did manage, in some way, to obtain perfectly intact specimens of these soft-bodied organisms. They were able to describe them in detail, and to establish whether or not they were already named. Many of these original type specimens can still be found in the museums today.

My interest in these animals has focused on their taxonomy and zoogeography. In this sense, the work has been a ‘back-to-basics’ of cataloguing faunas, identifying species, and establishing their geographical ranges. My Red Sea interests spread to the western Indian Ocean, as the two faunas show many similarities. However, it never ceases to amaze me how two very similar species may have completely different distributions, or how one species might only occur in one small patch, or another be widely distributed from one end of the Pacific to the end of the Red Sea. Like other marine molluscs, their study is a fascinating topic which still holds many secrets.

This species is a phanerobranch dorid, meaning its gills do not retract into a pocket. It is a fascinating species because it was only recorded twice in the Red Sea, the first time in 1828 then again in 1951, and never seen again. Then, last year I received this photo, with another this year, both from the Egyptian coast of the Red Sea. It is widespread throughout the Indo-West Pacific.

This stunning new species has been photographed half a dozen times in the last five years, despite divers photographing obsessively for the last 15 years or more. Only this year has a specimen finally been collected.

Another shockingly beautiful species with a crazy history. Described by a French woman in 1951, it disappeared until the last five years, when it was recorded in the Gulf of Oman, then the Gulf of Suez and the Gulf of Eilat.

There are no records from the main Red Sea. Sadly Razi Cohen died just before the book was published.

Platydoris pulchra is a cryptobranch dorid (like Glossodoris and Hypselodoris), and you can just see the pocket into which the gills retract for protection from predators. When the book was produced there was just one photo and I was unsure of its identity, but since then a dozen photographs have shown up from the Red Sea and the east coast of Africa, indicating that this rather rare species is limited to the Red Sea and western Indian Ocean.

Most aeolids have finger-like projections on their backs; at the tips there may be a sac storing the stinging cells of the hydroids and jellyfish on which they feed. Cuthona yamasui is very distinctive, despite only receiving a name recently. It is much more abundant in the West Pacific, but there are a handful of single records from the Red Sea, Persian Gulf, Gulf of Oman, western India, and Tanzania.

References

Yonow, N. 2008a. Sea Slugs of the Red Sea. Pensoft Publishers, Sofia, Bulgaria. 304 pp.

Note : - The book is available either through the publisher (http://www.pensoft.net/) or through me; you may email me on n.yonow@swansea.ac.uk if you would like a copy. I can offer it at the price of €75, somewhat variable in sterling due to fluctuating exchange rates (this includes P&P, bank charges, etc.).

Yonow, N. 2008b. Opisthobranchs of the Gulf of Eilat and the Red Sea: an account of similarities and differences. In: F. Por (ed.) Aqaba – Eilat, The Improbable Gulf. Environment, Biodiversity and Preservation. The Hebrew University Magnes Press, Jerusalem, 177 – 196.

Images

figure 1: Gymnodoris impudica (photo: Dray van Beeck)

figure 2 Glossodoris sp. nov. (photo: Sven Kahlbrock)

figure 3 Hypselodoris dollfusi (photo: Razi Cohen)

figure 4: Platydoris pulchra , (photo: Woody Pridgen)

figure 5: Cuthona yamasui (photo: Sven Kahlbrock)