A new species of Paracapillaroides (Nematoda: Capillariidae) parasitizing Nemadactylus bergi (Perciformes: Latridae) from the Argentine Sea.

A new nematode species, Paracapillaroides acanthocotylus sp. n., is described from the marine fish Nemadactylus bergi (Norman) (Latridae, Perciformes) from waters off Mar del Plata, Argentina (38 degrees 08'S, 57 degrees 32'W) (prevalence 81.8%, mean intensity 12.4 +/- 10.3). The new species is readily distinguished from P. agonostomi Moravec, Salgado-Maldonado et Caspeta-Mandujano, 1999, the only known species of the genus, by having in both sexes a longer oesophagus in relation to total body length. Males of the new species have a shorter and more complex spicule and a markedly different morphology of the spicular sheath; the rays supporting the caudal bursa are also shorter and rounded, instead of digitiform. Furthermore, females of the new species have elevated vulval lips and longer eggs. The complex structure of both the spicule and spicular sheath is unique among all capillariids parasitizing cold-blooded vertebrates. This is the first record of a species of Paracapillaroides in the southwestern Atlantic Ocean.