ON A NEW SPECIES OF HYSTEROTHYLACIUM (NEMATODA, ANISAKIDAE) FROM CAUQUE MAULEANUM (PISCES, ATHERINIDAE) BY BRIGHTFIELD AND SCANNING ELECTRON-MICROSCOPY

Hysterothylacium geschei n. sp. (Nematoda, Anisakidae) is described fr om the intestine of Cauque mauleanum (Steindachner) (Pisces: Atherinid ae) from Lake Panguipulli (39 degrees-43 'S; 72 degrees-13 'W), Chile. Eleven (78.6%) out of 14 fish were infected, with a mean intensity (r ange) of 14.4 (1-55) worms. The new species can be differentiated from the two previously described species of freshwater fishes from South America by the presence of lateral alae, the number of caudal papillae , and the length of the spicules, oesophagus, intestinal caecum, dista nce vulva-anterior extremity and the length ratio intestinal caecum: v entricular appendix. From the fishes examined in Lake Panguipulli, inc luding the introduced salmonid species Oncorhynchus mykiss (Walbaum) a nd the authochthonous species Basilichthys australia Eigenmann (Atheri nidae) and Percichthys trucha (Valenciennes) (Percichthyidae), only on e specimen of P. trucha was found parasitized by a third-stage larva o f this species.