Ptychogyliauchen, a new genus of Gyliauchenidae (Platyhelminthes: Digenea) from siganid fishes of the Indo-West Pacific

We propose a new genus of the Gyliauchenidae Fukui, 1929 ( Digenea), Ptychogyliauchen, gen. nov., for four new species that infect Indo-West Pacific siganid fishes. Ptychogyliauchen, gen. nov. is a morphologically distinctive genus, diagnosed principally by the presence of a highly convoluted oesophagus, which generally exceeds the total body length of the worm, and by the unusual folded structure of the ejaculatory duct. Ptychogyliauchen thetidis, sp. nov. is designated as the type species, and is described from the intestine of Siganus punctatus (Siganidae) from Heron Island, Great Barrier Reef, Queensland, Australia. Ptychogyliauchen himinglaeva, sp. nov. is described from the intestine of Siganus corallinus ( Siganidae) from Lizard Island, Great Barrier Reef, Queensland, Australia. Ptychogyliauchen leucothea, sp. nov. is described from the intestine of S. argenteus, and further recorded from S. fuscescens, off Ningaloo, Western Australia, Australia. Ptychogyliauchen thistilbardi, sp. nov. is described from the intestine of S. doliatus from Noumea, New Caledonia, and is also found in S. argenteus, S. canaliculatus, S. corallinus and S. spinus from Noumea, New Caledonia, and Moorea, Tahiti, French Pacific. Ptychogyliauchen thistilbardi, sp. nov. also occurs in the intestine of Chaetodon citrinellus (Chaetodontidae) from Moorea. A key to species is provided. All species have been described following morphological examination using light microscopy, and specimens of P. thetidis, sp. nov., P. leucothea, sp. nov. and P. thistilbardi, sp. nov. have been characterised using molecular methods. Sequences were obtained for a combination of nuclear ribosomal (28S (D1-D3) and ITS2) and mitochondrial (ND1) genes. A phylogenetic analysis of sequenced specimens of Ptychogyliauchen, gen. nov. was conducted using species of Petalocotyle Ozaki, 1934 for outgroup comparison. This analysis, based on alignments of the ITS2 and 28S (D1-D3) rDNA genes, supports monophyly of the geographically widespread P. thistilbardi, sp. nov., which is known from both siganid and chaetodontid hosts. We discuss the taxonomy of the genus and the host associations of each species and the group