Mediomastus fragilis Rasmussen (Polychaeta: Capitellidae), a species newly recorded from British Waters

Mediomastus Hartman (1944) is a genus of capitellid polychaetes with ten species of which only M. fragilis, described from the Danish Isefjord by Rasmussen (1973), has been found in European waters. In 1963 Clark & Dawson recorded the presence of an incomplete specimen of a capitellid from the west coast of Scotland and tentatively assigned it to Mediomastus. However, collections made by Dr P. E. Gibbs (Marine Biological Association, U.K.) in the Shetlands during April 1974 revealed a large number of capitellids subsequently identified as fragilis. More recently M. fragilis. has been recorded in large numbers during sampling programmes carried out by Dr A. Walker (Marine Science Labs., University College of N. Wales, Menai Bridge) in Dublin Bay and Liverpool Bay, and Mr J. Hunter (Highland River Purification Board, Dingwall, Ross-shire) has collected specimens from Dornoch Firth and Cromarty Firth, Easter Ross.