Re-examination of the phylogenetic relationships within the Gyliauchenidae Fukui, 1929 (Digenea) based on morphological and molecular evidence with a proposal for Paragyliaucheninae n. subfam. and a description of Flagellotrema convolutum Ozaki, 1936.

Flagellotrema convolutum Ozaki, 1936 was found parasitising the intestine of two new host fish species, the Indian sail-fin surgeonfish, Zebrasoma desjardinii (Bennett) (Acanthuridae), and the Picasso triggerfish, Rhinecanthus assasi (Forsskål) (Balistidae), from the northern Red Sea off Egypt. Another description of this species is provided with detailed morphological observations made of the genital systems. Using newly acquired molecular data from the D1-D3 regions of 28S rDNA, the phylogenetic relationships of subfamilies and genera within the Gyliauchenidae Fukui, 1929 are elucidated with morphological support. The Petalocotylinae Ozaki, 1934 and the Robphildollfusiinae Paggi & Orecchia, 1963 are recognized as valid subfamilies within the Gyliauchenidae. The Apharyngogyliaucheninae Yamaguti, 1942 and the Ichthyotreminae Caballero & Bravo-Hollis, 1952 remain junior synonyms of the Gyliaucheninae Fukui, 1929. Based on its unique position relative to all gyliauchenid subfamilies and its distinct separation from all other gyliauchenine genera, the Paragyliaucheninae n. subfam. is erected to contain Paragyliauchen Yamaguti, 1934. Paragyliauchen differs from all other gyliauchenine genera by having a pharynx differentiated into two, well-developed muscular regions: an anterior region composed of a ring with indented projections anteriorly and a posterior region that is ellipsoidal or barrel-shaped. Modified and/or new keys to the four subfamilies we recognize within the Gyliauchenidae as well as the genera within each subfamily are presented, and we discuss the evolutionary development and etymology of the unique anatomy of the anterior of gyliauchenids.

Redescription of Pseudolepidapedon balistis Manter, 1940 and a biological variant (Trematoda: Acanthocolpidae) from the Red Sea fishes; Balistoides viridescens and Rhinecanthus assasi.

During a survey of Red Sea fish parasites, two trematodes belonging to the genus Pseudolepidapedon Yamaguti, 1938 were encountered: P. balistis Manter, 1940 was found in the small intestine of the fish Balistoides viridescens and was redescribed for the first time from Egypt; adding many detailed morphological and ultrastructural characters. The second trematode was found in the small intestine of the fish Rhinecanthus assasi and found to represent a biological variant of the previous species as it differs from it in its generally smaller dimensions, shape of suckers and pharynx and the testes. SEM details of the first species were described for the first time illustrating the differences in the spination and papillae on different parts of the body; which may be of taxonomic importance in recognizing future different species of the genus.