Structure of the female cephalic end and cuticular ornamentations of Paraphilometroides nemipteri (Nematoda: Philometridae), as revealed by SEM

Abstract

Scanning electron microscopy (SEM) examination of a paratype specimen (gravid female) of the philometrid nematode Paraphilometroides nemipteri Moravec et Shaharom-Harrison, 1989, the type species of Paraphilometroides Moravec et Shaharom-Harrison, 1989, made it possible to recognise the true structure of the cephalic end and the shape of cuticular ornamentations on the body. In contrast to other philometrid genera, the cephalic end is angular in lateral view and rounded in dorsoventral view; large external cephalic papillae are fused together to form a marked dorsal and a ventral ala, each bent into a curve; six minute internal papillae, including a pair of previously not reported lateral papillae, were found; amphids were indistinct. Cuticular ornamentations (inflations) were found to be transversely elongated. These features, especially the unique cephalic structure, clearly distinguish Paraphilometroides from other philometrids and confirm the validity of this genus. Moravec and Shaharom-Harrison (1989) erected the hitherto monotypic philometrid genus Paraphilometroides Moravec et Shaharom-Harrison, 1989 with the type species P. Nemipteri Moravec et Shaharom-Harrison, 1989, described from females found in the fins and operculum of the marine fish (notchedfin threadfin bream) Nemipterusperonii (Valenciennes) from off the South China Sea coast, Malaysia. The male of P. nemipteri remains unknown. The authors distinguished Paraphilometroides from the related genus Philometroides Yamaguti, 1935 mainly by the unusual structure of the female cephalic end, which is unique within the family Philometridae (see Moravec 2006). However, P. nemipteri was studied only by light microscopy (LM), whereas some details of the cephalic structure, especially the cephalic papillae of gravid philometrid females are usually difficult to observe by LM due to a various degree of their reduction and atrophy (Moravec 2004); in the past, some philometrid species were even reported to have no cephalic papillae. Consequently, the only reliable method to study the cephalic structures in philometrids is the use of scanning electron microscopy (SEM). Therefore, one of the ethanol-preserved paratype specimens (gravid female) of P. nemipteri, deposited in the Helminthologi-cal Collection of the Institute of Parasitology, Biology Centre