Phyllobothrium squali Yamaguti, 1952 is redescribed and illustrated on the basis of the holotype from Squalus acanthias from Japanese waters and specimens from the same host off the Bulgarian Black Sea coast (new geographical record). The species is characterised by: a scolex diameter of 2.9-4.3 mm, a glandular apical organ, foliose bothridia with folded and posteriorly bifid margins, accessory suckers of 286-367 m in diameter, 222-373 testes per proglottis, an oval cirrus-sac with a length of 354-655 m, the vagina opening anteriorly to the cirrus-sac, and the terminal part of vagina with a circular musculature. Specimens from Etmopterus spinax off Naples, Mediterranean Sea, recorded by Euzet (1959) as Crossobothrium squali, are redescribed and their identification not confirmed. P. squali is recognised as a specific parasite of S. acanthias; it is presently known only from Japanese waters, the Black Sea and the Irish Sea. Changes to the generic diagnosis of Phyllobothrium, as given by Ruhnke (1996a), are proposed in order to include the characters of P. squali.