100 Years of Research on ‘Turbellaria’

Abstract

Comprehensive research on the ‘Turbellaria’ – or what are known now as the free-living platyhelminths – can mark its beginnings with the first monographic treatises on the group, foremost those by v. Graff, Lang, Wilhelmi and Benham. A major center for turbellarian research grew up around Graff in Graz, Austria, from 1884 through the first quarter of the 20th century; among its members were Bohmig, A. Meixner, J. Meixner, Reisinger and Steinbock. Other contributors to the major research effort in the later years of the 19th and early part of the 20th century were scattered in Germany, Italy, France, Scandinavia, Russia, Japan and the United States and included Hofsten, Steinmann, Wilhelmi, Sabussov, Beauchamp, Bresslau, Bock, Kenk, Ijima and Kaburaki. The attention to detail and accuracy of presentation by these early workers in Graz and elsewhere has made their contributions of long-lasting value. Between 1910 and 1960, modern research whose impact is still widely felt today took form. It includes studies in systematics (Luther, Karling, Hyman, Meixner, Beauchamp, Ijima, Ivanov, Mamkaev, Kenk, Papi, Riedl, Marcus, Ax), development (Bresslau , Reisinger, Steinbock), physiology (Hyman, Westblad), and genetics (Benazzi). Electron microscopy had a profound impact on morphological study starting in the 1970's, and the data it provided led to a new phylogenetic system of the Platyhelminthes as a whole, emphasizing the paraphyletic nature of the ‘Turbellaria’ within it. Systematic biology can be expected to make further advances by combining molecular methods with high-quality traditional taxonomic ones, still essential to this field. Other methodological advances spurring turbellarian research today include immunocytochemistry, molecular biology of nucleic acids, karyology and computational methods. Better understanding of nervous systems and muscle systems should come through studies in functional biology, immunocytochemistry, fluorescence microscopy and molecular biology. Understanding the early evolution of the brain as a control center in the nervous system will be especially interesting. Studies of structural and regulatory proteins as well as the newer microscopical techniques should provide insight into the regulation of cell proliferation, tissue growth, and embryonic development. Ecology and behavior are areas in which research efforts should be intensified. Culturing and the new techniques in molecular biology, microscopy and computational methods now allow the collection of quantitative, experimental data in these fields. Current karyological and biogeographical studies as well as work on the evolution of sex in hermaphrodites are encouraging signs that we might soon better understand many aspects of reproduction and of interactions of free-living platyhelminths in their ecosystems. Turbellarians remain important research subjects for reasons that inspired interest by even the earliest workers, the probability that they are the most primitive living representatives of the Bilateria.