Electric eel ancestors were cave dwellers

Here’s another series of taxa,
this time related to the infamous electric eel (Electrophorus, Figs. 1, 2) going back only as far as the Early Cretaceous bowfin, Calamopleurus (Figs. 1, 2).

We looked at
Kryptoglanis earlier here, and Electrophorus + cave fish earlier here. With fewer taxa and less understanding of shifting skull bones, I only guessed the conclusions proposed then and there… prior to adding Typhlichthys (Figs. 1, 2) to the large reptile tree (LRT, 1800+ taxa).

Typhlichthys subterraneus
(Girard 1859, 10cm) is the extant Southern cave fish and a killifish-mimic. This blind ambylopsid relative of Amia and the electric eel has a maxilla overlapping the premaxilla, a toothy palatine, two postfrontals, and three separate jugals. No pelvic fins are present. Scales are absent along with their pigment. Chemoreceptors dot the body. The vomer lacks teeth. The mandible is prognathus.

Kryptoglanis shajii 
(Vincent and Thomas 2011; 5.9cm long; extant) was originally considered an enigmatic subterranean catfish due to its barbels. Here it nests as an eel-knifefish with catfish-like barbels by convergence.

Gymnotus carapo
(Linneaus 1758; up to 100cm in length) is the extant banded knifefish, a nocturnal small prey predator with essentially no dorsal, caudal or pelvic fins. The anal fin undulates for slow propulsion. The electric signal is weak. A close relative is Electrophorus.

Electrophorus electricus
(Linneaus 1766, 2m in length) is the extant electric eel. Nearly blind, these appear to be derived from cave fish (above) let loose into fresh water rivers feeding into the Amazon. The electric organs, derived from muscles, form the majority of the body by volume.

References
Britz R, Kakkassery F and Raghavan R 2014. Osteology of Kryptoglanis shajii, a stygobitic catfish (Teleostei: Siluriformes) from Peninsular India with a diagnosis of the new family Kryptoglanidae. Ichthyological Exploration of Freshwaters. 24 (3): 193–207.
Girard C 1859. Ichthyological notes. Proceedings of the Academy of Natural Sciences, Philadelphia 11:56–68.
Linnaeus C 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.
Linneaus C von 1766. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio duodecima, reformata. pp. 1–532. Holmiæ. (Salvius)
Putnam FW, 1872. The blind fishes of the Mammoth Cave and their allies. American Naturalist v. 6 (no. 1): 6-30. Also published in: Packard, Jr. and Putnam 1872. Life in the Mammoth Cave, etc. chapter 3, pp. 29-54.
Vincent M and Thomas J 2011. Kryptoglanis shajii, an enigmatic subterranean-spring catfish (Siluriformes, Incertae sedis) from Kerala, India. Ichthyological Research. 58 (2): 161–165. doi:10.1007/s10228-011-0206-6.

wiki/Kryptoglanis_shajii
wiki/Electrophorus
wiki/ Spring_cavefish
wiki/Gymnotus
wiki/Amblyopsidae