Gymnorhamphichthys rosamariae, a new species of knifefish (Rhamphichthyidae, gymnotiformes) from the upper Rio Negro, Brazil

Abstract

Based on several collections made in the upper Rio Negro in 1979 by Dr. M. Goulding, Gymnorhamphichthys rosamariae is described as a new species in the gymnotiform family Rhamphichthyidae. It is different from the other two species, G. rondoni and G. hypostomus, by its substantially larger size, a greater number of electrocytes in the submental accessory electric organ, and by having a more compact head with a blunter snout. Regarding body proportions, the newly described taxon has a relatively shorter abdominal, and longer caudal vertebral column. It also is much less pigmented than the two species, no dorsal nor lateral markings are present and the caudal appendage is unpig‐mented. The number of anal fin rays and number of caudal vertebral centra are like in G. hypostomus, and much higher than in G. rondoni. Cycloid scales are found in all three species on the posterier third of the body only. The three species were found syntopically in the upper Rio Negro.