Temperature, taxonomic technique and the zoogeography of lugworms (Arenicolidae, Polychaeta)

Abstract

1. The surface of the world may be divided into three great zones, each with a completely distinct lugworm fauna on its shores. The boundaries correspond roughly with the summer surface-water isotherms at 20° C, and they separate a northern cool-water, a warm-water and a southern cool-water zone. The third zone shows a subdivision of minor importance along the line of the 10° C isotherm. 2. The main zones are characterized by endemic clusters of forms which seem to have evolved and differentiated within the zones. The temperature barriers must therefore have persisted for long enough to allow a considerable degree of intrazonal evolutionary differentiation to take place. 3. Until ten years ago, our classification of the Arenicolidae was based almost entirely on museum material, the samples being mostly small and sometimes ill-preserved. In the circumstances, taxonomists could use only very obvious characters, and they tended to make their groups too large. 4. Recent work with large samples of worms, combining field with laboratory study, has split several of the older taxa. The number of named species and subspecies of lugworms has risen in ten years, mainly as a result of splitting, from 10 to 24. 5. The importance of temperature barriers, and of other isolating factors, in controlling lugworm distribution is now more clearly seen. It may be that similar studies, carried out on other families, would substantially reduce the number of polychaetes supposed to have wide (bipolar or cosmopolitan) distributions. © 1964 Biologischen Anstalt Helgoland.