Development of <i>Philometroides seriolae</i> (Nematoda: Philometridae) in a Surrogate Intermediate Host <i>Tigriopus japonicus</i> (Copepoda: Harpacticidae)

The development of first to third stage larvae of Philometroides seriolae, the type species of the genus, was monitored. Hatched larvae were obtained from gravid females collected from Japanese amberjack Seriola quinqueradiata. The larvae in the uterus consisted of the first stage (18.4%) and second stage (81.6%). Larvae obtained from the uteri were exposed to the harpacticoid copepod Tigriopus japonicus, employed as a surrogate intermediate host. Infected copepods were maintained at 20°C and at 25°C for 28 days, during which larvae in the hemocoel were periodically examined. All larvae had developed into second stage by 5 days post exposure (5 dpe). Third stage larvae first appeared at 13 dpe at 20°C and at 8 dpe at 25°C. First to third stage larvae possessed two unicellular oesophageal glands located in the posterior region of the oesophagus. The second stage larvae possess single papilla-like projections at the surface of cephalic region and the caudal end. In the third stage larvae, these projections were liberated from the surface with peeling of the second stage sheath. This study provides the first description of the second and third stage larvae of P. seriolae and documents their experimental development in a copepod host.