Two species of
Anthopleura, A. ballii and
A. thallia , co-occur in Northern Europe with
Bunodosoma biscayensis , a species closely allied to
Anthopleura . The historical factors underlying their distribution are here investigated as part of a preliminary phylogenetic analysis of morphological data. Based on this analysis,
Bunodosoma is nested within
Anthopleura, and
B. biscayensis is more closely related to members of
Anthopleura than to other members of
Bunodosoma . Because
B. biscayensis also has adhesive verrucae, rather than non-adhesive, rounded vesicles, it is transferred to
Anthopleura . The tree consists of two major clades, each of which includes species from the Atlantic and the Pacific. The tree shows geographic structure: one clade includes species found only in the Northern Hemisphere, and the other includes widespread species and species found only in the Southern Hemisphere. Although all of the European species of
Anthopleura are part of the Northern Hemisphere clade, none are one another’s closest relative.
