Monostephanostomum nolani sp. n. is described from Carangoides plagiotaenia Bleeker, off Lizard Island, Great Barrier Reef, Queensland, Australia. It differs from all other species in the genus except M. manteri Kruse, 1979 in that the vitellarium reaches into the forebody. It differs from M. manteri in the ventral hiatus in the circum-oral spine row, the extent of the vitellarium in the forebody, where it is not confluent, its elongate pharynx and its smaller eggs. Monostephanostomum krusei Reimer, 1983 is redescribed from Pseudocaranx dentex (Bloch et Schneider) from Ningaloo Reef off Western Australia. It is considered similar to M. nolani, differing in the vitellarium being restricted to the hindbody, but sharing with M. nolani an unusual arrangement of small body-spines on the antero-ventral surface. It is also morphologically very similar to Monostephanostomum roytmani (Parukhin, 1974), which apparently lacks the diminutive antero-ventral body-spines. A key to eight recognized species in the genus is presented.
The genera Preptetos Pritchard, 1960 and Neopreptetos Machida, 1982 are redefined. The following species are described and/or recorded from marine fishes. From the Great Barrier Reef: Preptetos caballeroi Pritchard, 1960 in Naso annula-tus, N. brevirnslris and N. vlamingii·, P. xesuri (Yamaguti, 1940) in Zebrasoma veliferum and Z. scopas; Preptetos cannoni Barker, Bray et Cribb, 1993 in Siganus dolialus and S. fuscescens', Preptetos laguncula sp. n. in Naso unicornis (type-host); P. impar sp. n. in Lutjanus erythropterus (type-host) and L. malabaricus·, Neopreptetos arusettae Machida, 1982 in Pomacanthus semicirculatus·, and N. kurochkini (Toman, 1989) in Chaetodontoplus meredithi. From southwestern Australia: Preptetos rotto sp. n. in Nelusetta ayraudi (type-host), Neosebastes pandus, Oplegnathus woodwardi and Pagrus auratus. The new combination Preptetos trulla (Linton, 1907) (originally Distomum then Lepocreadium) is made and the species Lepocreadium areolatum (Linton, 1900) is considered likely to belong in Preptetos.