Description of Ophthalmonema diodontis gen. et sp. n. (Nematoda: Cystidicolidae), a parasite of the eye and surrouding tissues of porcupinefishes (Diodon spp.), with a key to cystidicolid genera.

A new nematode genus and species, Ophthalmonema diodontis gen. et sp. n. (Cystidicolidae), are established based on female specimens (males remain unknown) collected from both eyes of an aquarium-kept spot-fin porcupinefish, Diodon hystrix Linnaeus (Diodontidae, Tetraodontiformes), originally caught in coastal waters off Florida, USA. Examination by light (LM) and scanning electron microscopy (SEM) revealed that the mouth structure of this nematode, particularly the presence of two conspicuously large, rounded, opposing dorsoventral plates, each connected by a narrow bridge to the inner end of the pseudolabium, is unique among all cystidicolid genera. Inadequately described cystidicolid nematodes previously reported from the eye and surrounding tissues of D. hystrix and Diodon nicthemerus Cuvier in the Caribbean Sea and in waters off southern Australia, respectively, as Metabronema sp. or Cystidicolidae gen. sp. are considered to belong to the new species O. diodontis. A key to cystidicolid genera is provided.