Andy, Eduard, Perhaps a species definition within a single genus (some, but not all genera)can be written and agreed upon based upon only conchologic characteristics. But to get real agreement, you would need to use soft part information to show that the hypothesis works consistently. You might be able to expand to similar genera, but not without some controversy. Perhaps this can be done for Paleozoic species where we have no soft part data, but again the limits of variation within populations and between populations vary, so what works for one may not work for another. Allen Aigen [log in to unmask] -- Andy Rindsberg <[log in to unmask]> wrote: Eduard Heiman wrote, > Perhaps one possible way to move forward with species problems is to go from simple to more complicated: first agree on species definition from a conchological point of view and after that to think about more complicated biological aspects of the problem. In such a way we can at least gather facts and understand better what we are talking about. I do not think that number of species and subspecies "depends on your personal approach to taxonomy and the purposes and methodologies of distinguishing between one species and another." We need definitions of taxa, which are more or less in consensus and understandable to most of us. If I understand you correctly, you want a species definition that treats shell characters ("conchological point of view") as more important than soft parts ("more complicated biological aspects"). Some kinds of soft parts are reflected in the shell, such as the muscles and siphons. And in fossils, usually the shell is the only part that is available for study. But for living mollusks, it's a different situation. Since some species have no shell, and some others cannot be distinguished without observation of parts other than the shell, it is not possible to construct an accurate taxonomy of mollusks without reference to the soft parts. Indeed, in the freshwater unionids, shell characteristics can be so variable as to make DNA analysis necessary to classify species meaningfully. Just ask David Campbell! Shell characters can still be used to make identification keys, of course, and visual observation of shells is still the most cost-effective way to identify MOST mollusks. And great progress is being made as observers pay closer attention to the early stages of mollusks, which are often quite different from the adult stages, and are often relatively conservative. But shell characters will often be trumped by soft parts, and certainly by DNA, where the taxonomy of a species is in question. Cheers, Andrew K. Rindsberg Geological Survey of Alabama ---------------------------------------------------------------------- [log in to unmask] - a forum for informal discussions on molluscs To leave this list, click on the following web link: http://listserv.uga.edu/cgi-bin/wa?SUBED1=conch-l&A=1 Type your email address and name in the appropriate box and click leave the list. ---------------------------------------------------------------------- ---------------------------------------------------------------------- [log in to unmask] - a forum for informal discussions on molluscs To leave this list, click on the following web link: http://listserv.uga.edu/cgi-bin/wa?SUBED1=conch-l&A=1 Type your email address and name in the appropriate box and click leave the list. ----------------------------------------------------------------------