Originally, a group of Teleost fishes from the rivers and lakes of Old Earth's Africa, comprising 18 genera and some 200 species. By the late Information Age most were extinct in the wild due to over-fishing, pollution and diversion of watercourses, and the introduction of foreign predators and parasites. They persisted only as a few species kept by zoos and by hobbyists, and as records in gene banks. The original species were notable for two related traits. First, they were among the relatively few Old Earth species that were weakly electrogenic and strongly electrosensitive. Secondly, and very probably a trait related to the first, they had the largest brains of any Old Earth fish, giving them an encephalization quotient comparable to that of baseline apes (including humans) or cetaceans. Most of this brain matter was cerebellum, devoted to the interpretation of their electrical fields as well as the natural electrical fields of other life forms. However, they were capable of fairly complex thought, manifested in a rich repertoire of play-like behaviours. Mormyrids lived in muddy waters, or were nocturnal, or both, and used their electrical sense to detect food, predators, and inanimate features of their environment. Many mormyrids had a long snout, sometimes with a trunk-like appendage, which they used to probe the sand or mud of the river bottom for food.
The surviving species of mormyrids have attracted the attention of provolution groups because of their large brains and apparent intelligence. There are several minor clades of Actie provolves based on one or more of the mormyrids, and one moderately well known clade, the Kanumae.
Subsapient life forms based on mormyrids are commonly used in biologically based habs, especially in the Zoeific Biopolity, where they are ubiquitous in the water supply systems. Their relatively high intelligence, their ability to detect tiny variations in electrical and magnetic fields and to navigate in complete darkness, and the sensitivity and dexterity of the "trunk" make them useful in hab maintenance. A few varieties have enhanced electrogenic ability as an aspect of system security, and can generate 500 or more volts, but this is rare; usually splices derived from other species that are naturally stronger generators (torpedo rays, electric "eels" or electric catfish) are employed for such work.
Some, perhaps even many or all, of the original mormyrid species have been restored to their original habitats on Old Earth, presumably either from stock confiscated by GAIA from hobbyists or scientists or else lazurogened from data in the caches of the Burning Library Project. Pilgrims visiting historical sites along the Old Earth's Nile have noted that the local Children of Gaia seem to regard the local mormyrid species as holy; this is a resurrection of an ancient Egyptian belief.