Four polyopisthocotyleans (Platyhelminthes: Monogenea) from carangid fishes in the Mediterranean, off the Algerian coasts.

Four polyopisthocotyleans were collected from the gill filaments of carangids from off the Algerian coast, southern Mediterranean. Specimens of van Beneden & Hesse, 1863 (Gastrocotylidae) and cf. Dillon & Hargis, 1965 (Heteraxinidae) from the Mediterranean horse mackerel (Steindachner), (Meserve, 1938) (Heteraxinidae) from the greater amberjack (Risso) and Euzet & Ktari, 1970 (Pyragraphoridae) from the pompano (Linnaeus) are redescribed based on newly collected specimens. Their taxonomically important morphological features (male copulatory organ and clamp sclerites) are described and illustrated, and the morphometric variation between Mediterranean and oceanic specimens is highlighted. Careful examination of the specimens of Sproston, 1946 from the Mediterranean revealed that they exhibited unusual features compared with Dillon & Hargis, 1965 from the Pacific, mainly the absence of the terminal lappet, thus questioning previous records of this species in the Mediterranean. New geographical locality records are provided for and . The presence of cf. and in the Mediterranean is noteworthy as these monogeneans were initially described in the Pacific Ocean. This study extends the geographical range of to the southern Mediterranean.