INTRODUCTION, AND ECOLOGICAL AND SYSTEMATIC BACKGROUND, TO THE TERRICOLA (TRICLADIDA)

Terrestrial flatworms are carnivorous soil animals which maintain thei r moisture requirements by vertical migration through a continuum of m icrohabitats between soil, litter and vegetation. Over 800 species are known and several show human-mediated distribution patterns. Recent m olecular studies of the Tricladida have cast doubt on the monophyly of the Terricola. The taxonomy of the terrestrial flatworms is in a stat e of flux, and the classification of austral taxa hampered at present by the apparent numerous species complexes. Worldwide only some 55% of named species are adequately known histologically, and further compar able anatomical descriptions are essential for advancing their taxonom y. Distribution of the Terricola, especially at subfamily level, is be st explained by the vicariance mechanisms of plate tectonics. The low vagility of the Terricola makes them particularly useful for biogeogra phical studies.