I B RAR.Y OF THE UNIVERSITY OF ILLINOIS 5SO.5 FI CV' Return this book on or before the Latest Date stamped below. A charge is made on all overdue books. University of Illinois Library EC 12 1948 M32 ZOOLOGICAL SERIES OF UNIVERSITY OF ILLINOIS FIELD MUSEUM OF NATURAL HISTORY Volume 24 CHICAGO, JANUARY 30, 1940 No. 11 A TENTATIVE CLASSIFICATION OF THE PALEARCTIC UNIONIDS BY FRITZ HAAS CURATOR OP LOWER INVERTEBRATES INTRODUCTION The arrangement which is to follow is based upon more than thirty years' experience in work on unionids in general and on the palearctic ones in particular; it aims to place the pearly fresh-water mussels of the palearctic region within the general system of the unionids, and to show the natural inter-relationships of the forms. This requires some mention of earlier taxonomic essays on the subject. Until the middle of the last century, that is to say, until the time of Rossmaessler in Germany and Dupuy in France, Linnaean methods prevailed; every animal believed to be unknown to science was described as a new species and nobody worried about the natural relations of the "species" thus originated. This being so, it is not surprising to find that many phaenotypic features were mis- taken for specific ones and that many forms which had nothing to do with each other were thrown together. It seems that Rossmaessler was the first to recognize clearly the transformation of the unionid shell by environmental conditions; he, at least, knew about the shaping influence of lacustrine life, which manifests itself in the larvation of the still specifically characteristic juvenile shell, or in that of the fluviatile phase of unionids. The following era may be characterized by the methods of J. R. Bourguignat and his pupils — Locard, Servain, Coutagne, and many others. This nouvelle ecole attributed specific value to all the differ- ences of shape in fresh-water mussels, which may have originated through environmental influences as well as through geographic isolation. Under this school, discrimination went far more into detail than under the Linnaean method: each shell which differed from an already known mussel in three dimensions, or by the indices calculated from them, was a new species. It is obvious that such a No. 464 115 116 FIELD MUSEUM OF NATURAL HISTORY — ZOOLOGY, VOL. 24 method, because of the impossibility of securing exact measurements in the always somewhat ventricose unionid shell, could afford approximate figures only; it led inevitably to the description of every individual examined as a new species. Umbonal sculpture and details of the hinge composition were not considered at all. Thus, convergencies due merely to similarity of measurements in the three dimensions, often led to unwarranted inferences with regard to natural relations. The placing of Margariti/era margariti- fera and of Psilunio littoralis close to certain elongated forms of crassoid unios affords an example. Truth compels us to admit that, leaving aside slips of judgment due to deficiencies of the method, the natural arrangement of the many described "species" was not spoiled; on the contrary, they generally were united into groups, which correspond to a certain degree to our modern racial groups. The geographical factor, how- ever, without which a natural taxonomic arrangement can not now be imagined, does not play any role in the Bourguignatian method, nor was the anatomy of the soft parts considered. Another Frenchman, H. Droue't, stands quite alone among his contemporaries, by reason of the emphasis he placed upon the con- nection between the shape of his new unionids and the life conditions of their respective habitats. Droue't was, indeed, a pioneer, but he knew too little about the ecology of fresh-water mussels and was therefore often deceived by convergent shapes. After Rossmaessler's death, at a time when descriptions of new unionids were produced by the hundreds in France, in Italy, and in other countries, work on fresh-water mussels lagged in Germany. The German malacologists (especially Kobelt, who continued Ross- maessler's incomplete Iconographie} did not agree with Bourguignat's views, which were also in disfavor with some of the French spe- cialists; for example, with the editors and collaborators of the Journal de Conchy 'liologie. Kobelt's disapproving attitude had won him Bourguignat's intense hatred, but he kept to his own ideas on unionids, which he did not publish until after Bourguignat's death. The list of the Unionidae in C. A. Westerlund's Fauna der in der palaarctischen Region lebenden Binnenconchylien (7, 1890) shows how Bourguignat and his school, to which Westerlund belonged, believed the fauna of palearctic fresh-water mussels to be composed. More modern ideas on this subject originated with Kobelt, who, in various publications, pointed out the isolating effect of hydro- graphic frontiers. By many examples he tried to prove the theory, THE LIBRARY OF THE 1940 PALEARCTIC UNIONIDS — HAAS FFR1^?) 1QAH upon which his principal conclusion was based, that a^llRSffi&Pf ILLINOIS arrangement of the unionids had to take into consideration their distribution in the different hydrographic systems. When this view was accepted, and it was understood that the overwhelming num- jber of described palearctic unionids must be reduced to a very ol limited number of "fundamental" species, there was the unfortunate 0 circumstance that nobody knew which these fundamental species gmight be. Everyone agreed, at least, that these fundamental species, which- Oever they might be, had given origin to local races in the different ^ parts of the river systems inhabited by them. Collectors and scien- cotists — among them, thirty years ago, even the writer of these "-'lines — began to prove the existence of these local races and to