The Tube-WormSpirorbis Vitreusand its Distribution in Britain

Abstract

Spirorbis vitreus (Fab.), an arctic form, seems to be absent from Wales and most of England, but is generally abundant off the west coast of Scotland and also occurs in certain localities off Ireland, the Isle of Man, Cornwall and Brittany (which is probably its southern limit in Europe). Its range thus extends farthest down our western coasts, a distribution which is characteristic of various other northern and southern forms that are near the limits of their geographical ranges. Such species presumably benefit from the equable temperatures, adjoining deep water, and this winter-breeding species of Spirorbis also needs freedom from abrasion.The tubes of juvenile S. vitreus are very different from those of adults. The distribution of uncini on the abdomen shows a remarkable bilateral asymmetry, as in S. spirillum.