..Click
An Image To Visit Society Website
|
|
|
|
..Click
An Image To Visit Society Website |
||
 |
1st
International Aplacophoran Workshop and Symposium - Characters
and Techniques With their basal position in the molluscan tree of life the aplacophorans have been the focus of much interest in the past years. However, there has not been a meeting before devoted to this group where the focus could be on coordinating our research efforts. The meeting was opened with a discussion led by Amlie Scheltema, Woods Hole Oceanographic Institution, on what constitute characters, homologies, and structures in generalAlthough there was general agreement on the structures and features of an organism, there was a heated dispute on what actually was a good character, whether taxa can be defined on the basis of characters, and how to define homologies. Finally there was a general agreement that a putative taxic homology is a piece of evidence for the existence of a monophyletic group. The phylogenetic position of Cambrian fossils like Wiwaxia and Halkieria have spurred the discussion of the limits of the phylum.It was therefore of great interest that Derek Briggs, University of Bristol, introduced new data on the enigmatic Silurian fossil Acaenoplax hayae. The organism was described as a mollusc by Briggs and his co-workers [3], but this view has been challenged, with arguments that it instead should be placed within the Annelida. Acaenoplax has features in common with both molluscs and annelids, so that it is difficult to place it within extant phyla. The problem with disarticulated hard parts was also made obvious, since fossils of a similar type, but with only the hard parts preserved, were known earlier from Gotland. Similar problems were demonstrated by Anette Hgstrm, University of Uppsala, who talked about Plumulites and other sclerite-bearing fossils. The definitive placements of these fossils are still uncertain, and the advantages for palaeontologists and neontologists to work together became obvious. Since the theme for the meeting was characters and techniques it was natural that many talks and a large part of the discussion focused on the usefulness of different types of structures in describing new taxa. A major problem today is that different research groups tend to use different character sets in describing new species and higher taxa. These differences make it difficult to compare results and to make studies of the phylogeny of aplacophorans.Dimitry L. Ivanov Moscow State University, talked about useful characters in caudofoveates.There is less disagreement in the descriptions of Caudofoveata than in the other major clade of Aplacophorans, the Neomeniomorpha, or the Solenogastres as they also are called. Amlie Scheltema introduced a number of useful hard-part anatomical characters in the study of Neomeniomorpha, and she also discussed the possibilities of coding these characters for a cladistic analysis.In addition to this she also demonstrated methods for the preparation of slides for description and species identification from these characters. Her list of characters mostly focused on radula, sclerites (the general term adopted by all to replace "spicules" and "scales" as they are presently called in the literature), and copulatory spicules in the light of their shape and arrangement. Luitfried von Salvini-Plawen, University of Vienna, on the other hand, went through a number of soft-anatomy features that he considered informative at various taxonomical levels.A large number of features were mentioned and added up to an interesting lesson in neomeniomorph anatomy. The usefulness of additional characters were demonstrated by Bernard Ruthensteiner, Zoologischer Staatssammlung, Munich, and by Kennet Lundin, Universeum, Gothenburg, who had studied various aspects of the ultrastructure of aplacophorans. It was shown by Lundin that the epidermal cilia and their rootlets hold useful information for cladistic analyses, and he spoke about the future of his studies of these structures that will include many additional taxa. Ruthensteiner has studied the larva of a chaetodermomorph, and could among other findings report the presence of a protonephridium in this group.Additional information on the embryology and larvae of chaetodermomorphs was introduced by Claus Nielsen, Zoological Museum, Copenhagen, who importantly demonstrated the presence of shell-fields and dermal papillae in the growing larvae. These papillae had a striking resemblance to the papillae shown by Briggs in Acaenoplax earlier which spurred an interesting discussion.Akiko Okusu, Harvard University, was not able to attend the meeting, but a talk prepared by her was held for her on the embryology and development of the neomeniomorph Epimenia babai. Also here similar papillae were found in the larvae.Her results pointed out many interesting similarities to the embryonic development of other molluscan groups. On the technique part of the meeting Claudia Handl, University of Vienna, demonstrated new methods for serial ultra-thin sectioning.A major problem is that many of the aplacophoran species are tiny, often less than two millimetres, so that in order to identify all organs in a series of sections, the sections have to be thin (less than 2 um In connection with this talk, Christiane Todt, University of Vienna, showed various staining techniques for epon embedded histological material.This also gave rise to a lively discussion about the pros and cons of various resins for ultra- and semi-thin sectioning. Molecular methods have not been used to any significant extent in the study of aplacophorans.A reason for this is that the animals are often difficult to obtain, and most material in archival collections has been fixed in formaldehyde, which is not generally considered a good medium for preserving DNA for molecular related work. Christoffer Schander, University of Gothenburg, showed however that it is possible to use formaldehyde fixed material and gave some dos and donts on the use of archival material in general, and especially on formaldehyde fixed material. Matz Berggren, Kristineberg Marine Research Station, demonstrated the advantages of using the computer program Delta for making species descriptions and taxonomic keys. Since the keys are not necessarily dichotomous it would be possible to use them even if there is no consensus of how aplacophoran taxa should be described. It would also be useful for identifying gaps in present taxonomic descriptions.Other types of data bases were demonstrated by Torben Kling Petersen, Sun Microsystems.He noted that much effort is put into databases that are not going to be functional within a decade since they are built on non-standard principles using non-standard software.He demonstrated the advantages of the present aplacophoran FileMaker Pro database: Accessible at http://www.whoi.edu/science/B/aplacophora. The majority of the participants of the workshop agreed that forthcoming taxonomic descriptions ought to be put into this database and that it must be made complete in terms of older descriptions. The desirability of publishing a list of useful characters on the net was briefly discussed, and personal interactions begun at the workshop should continue in the future. A second meeting is already being planned for two years hence, as this first meeting/workshop was received with enthusiasm spiced by our differences of opinion. The organizers felt that such a meeting has enhanced, not just the taxonomic efforts of those working on the Aplacophora, but also the global efforts to describe the great diversity of life on our planet and their evolutionary relationships. Acknowledgements The organizers are thankful to the staff at Kristineberg Marine Biological Research Station for providing excellent conditions for the meeting, and to the Royal Swedish Academy of Sciences, the Wenner Gren foundation, The EU ARI program, the Swedish Biodiversity Organization, the Gothenburg Marine Research Council, and National Science Foundation PEET program for financial support. References 1. Halanych, K. M. et al (1995) Evidence of 18S ribosomal DNA that the lophophorates are prostome animals. Science 267, 1641-1643 2. Aguinaldo, A. M. et al. (1997) Evidence for a clade of nematodes, arthropods and other moulting animals. Nature 387, 489-493. 3. Sutton, M. D. et al. (2001) An exceptionally preserved vermiform mollusc from the Silurian of England. Nature 410, 461-46 Christoffer Schander Department of Biology, Redfield 1-34 Woods Hole, Ma 02543, USA Aplacophorans: Above: Helicoradomenia sp., a neomeniomorph. [Photo: A. Scheltema]Right: Chaetoderma canadense, a chaetomorph [Photo: R Robertson]. Illustrations to follow. |
|
|
