An updated concept and revised composition for Hamacreadium Linton, 1910 (Opecoelidae: Plagioporinae) clarifies a previously obscured pattern of host-specificity among species Author Martin, Storm B. Author Cutmore, Scott C. Author Ward, Selina Author Cribb, Thomas H. text Zootaxa 2017 4254 2 151 187 journal article 33240 10.11646/zootaxa.4254.2.1 64b0d4b0-479e-484a-aaf5-d5237292d4a5 1175-5326 545862 0BDF72E4-5330-4EE7-8560-DF44E71C1F41 Hamacreadium phyllorchis ( Bilqees, 1976 ) Cribb, 2005 ( Figure 5 b) Synonyms: Olivacreadium phyllorchis Bilqees, 1976 ; Olivacreadium heterorchis Bilqees, 1976 n . syn. ; Hamacreadium heterorchis ( Bilqees, 1976 ) Cribb, 2005 n. syn. Records. From the olive grunt, Pomadasys olivaceus (Day) (Haemulidae) , as O . phyllorchis and from the golden snapper, Lutjanus johnii , as O . heterorchis , off Pakistan by Bilqees (1976) . Remarks. Bilqees (1976) proposed Olivacreadium for O . phyllorchis and O . heterorchis , but only made comparisons with freshwater species of Eucreadium Dayal, 1950, without considering Hamacreadium and other relevant plagioporine genera. Cribb (2005a) transferred both species to Hamacreadium , synonymising Olivacreadium . Bilqees (1976) considered the two species distinguishable by egg size, relative development of ventral sucker musculature, sucker width ratio, uterine metraterm, cirrus-sac structure and genital pore position. However, none of these differences is compelling, largely because each species was described based on a single flattened specimen; the reported egg sizes overlap substantially (60–67 × 37–46 vs 60– 68 × 32–40 µm), the differences in the ventral sucker muscular appear to be overstated, the shape of the cirrus-sac and the sucker width ratios are distorted by flattening and the visibility of the metraterm and the observed difference in the position of the genital pore may be considered intra-specific variability. Hamacreadium heterorchis is therefore considered a junior synonym of H . phyllorchis here. The only discrepancy between H . phyllorchis and the concept of Hamacreadium is the excretory vesicle, which Bilqees (1976) described as reaching only to the testes, although her illustration depicts an open ended excretory vesicle suggesting, perhaps, that the excretory vesicle could only be followed to the testes. If the excretory vesicle is restricted to the hindbody, this species would be more comparable to those of Neolebouria , particularly Neolebouria capoori Jaiswal, Upadhyay, Malhotra, Blend, Dronen & Malhotra, 2014 , known from a nemipterid in Indian waters. Haemulids are closely related to lutjanids but have only been reported as hosts of H . mutabile on three occasions (Table 1). Because Bilqees (1976) reported a single worm and a low prevalence (2.6%, from 39 fish), it seems likely that P . olivaceus is only an incidental host of H . phyllorchis .