A new type of advanced third-stage larvae of the genus Gnathostoma in freshwater eels, Fluta alba, from Nakhon Nayok, central Thailand.

Five advanced third-stage larvae of a newly identified type of genus Gnathostoma were collected from freshwater eels, Fluta alba, which were purchased at a market in Nakhon Nayok, central Thailand. The most remarkable characteristic of the newly identified larvae was the larger body size compared with any other larva of Gnathostoma spp. They were also distinguishable from other species by the shape of their hooklets, which branched in a complex manner at the base: this had not been previously observed in any other larval Gnathostoma. The newly described larvae had an average number of 44.5, 45.0, 49.0 and 55.1 hooklets on the head-bulb from the first to the fourth rows, respectively, which were comparable to those of larval G. spinigerum. However, the average number of nuclei in each intestinal cell was 2.21 and fewer than those of the larvae of G. spinigerum. These results suggest that the new type of larvae belong to either G. vietnamicum, G. malaysiae, or constitute a new species of the genus Gnathostoma.