Fishes Class Actinopterygii Woodward, 1891 - ray-finned fishes Order Gymnotiformes Rafinesque, 1810 - American knifefishes 1 Family Sternopygidae - glass knifefishes 2 Family Apteronotidae - ghost knifefishes 3 Family Rhamphichthyidae - sand knifefishes 4 Family Hypopomidae 5 Family Gymnotidae Rafinesque, 1815 - nakedback knifefishes 6 Family Electrophoridae - electric knifefishes see Family Gymnotidae Rafinesque, 1815