New data on the morphology of Nilonema senticosum [Nematoda, Philometridae], a parasite of Arapaima gigas [Pisces], with notes on another philometrid, Alinema amazonicum, in Peru

Female specimens of a little-known philometrid nematode, Nilonema senticosum (Baylis, 1927), were collected from the swimbladder of the arapaima, Arapaima gigas, from the Amazon River basin (Iquitos, Loreto District) in Peru. Scanning electron microscopical (SEM) examination, used for the first time in this species, made it possible to reveal some taxonomically important, previously unreported features of N. senticosum, such as the presence of minute cephalic papillae (10 papillae in 2 circles) and amphids surrounding the small oral aperture, and to confirm the absence of an anal opening in this species. Males and females of another philometrid, Alinema amazonicum (Travassos, 1960), were recovered from the body cavity of the pimelodid catfishes Calophysus macropterus and Brachyplatystoma juruense (a new host record) from the Amazon River basin (fish market in Iquitos, Loreto District) in Peru. SEM examination, not previously used in the male of A. amazonicum, enabled to study in detail the male cephalic and caudal structures.