On the taxonomic status and distribution of Chthamalus stellatus (Cirripedia) in the north-east Atlantic region: with a key to the common intertidal barnacles of Britain

Abstract

During his studies on the Cirripedia Darwin (1854) gave much attention to the Chthamalidae, and his views of the species remained unchallenged for many years. Darwin's attitude to speciation appears to have been coloured by his concurrently developing theories of natural selection, and he was especially interested in the existence of wide variation within species. Thus Chthamalus stellatus as described by Darwin consisted of a number of races or varieties, and was of almost worldwide distribution (‘southern England, Ireland, Isle of Man, Mediterranean, Madeira, Cape Verde Is., southern United States, West Indies, Brazil, Rio Plata, Red Sea, Philippines, China, Gulf of Korea, Oregon or N. California’). This distribution has been considerably narrowed in the last 60 years, and recent investigators have raised varieties to specific rank, or described new species and subspecies. In North California and Oregon we now have the full species C. dalli (Pilsbry, 1916); along the eastern coast of U.S.A. we now have C.fragilis (Pilsbry, 1916); in the Caribbean and along the east coast of South America we have C. angustitergum and C. bisinuatus (Pilsbry, 1916; Ross, 1969; Southward, 1975); for the Indopacific region there are now the species C. challengeri and C. malayensis (Hoek, 1883; Pilsbry, 1916); and in the Mediterranean, C. depressus (Poli), which was reduced by Darwin to a variety of C. stellatus, has been raised again to specific rank (Barnes, 1956; Utinomi, 1959; Southward, 1964; Klepal & Barnes, 1975) and is now assigned to the genus Euraphia (Newman & Ross, 1976). Thus except for a few dubious records what remains of Darwin's C. stellatus is confined to Europe, N. Africa and W. Africa (Southward, 1964; Stubbings, 1967). Nevertheless, even such a reduced distribution encompasses several distinct climatic zones, and seems more extensive than the individual ranges of the three species (C. dalli, C. fissus and C. panamensis) found in comparable climatic regions of the N.E. Pacific.