Red Phantom Tetra

Megalamphodus sweglesi has a maximum standard length of 3.2 cm (1.3 in). This species has no less than three colour forms, varying from a silvery, transparent form through to a red form. It is thought that the colour is determined by habitat, with the ligher coloured fishes being found in clear waters, and the red forms coming from blackwater. This species is shallow bodied in comparison to its congeners, with its depth fitting into its standard length 2.71 to 2.9 times. There is a black humeral spot, and females can have a black stripe, with cream edges, running along their dorsal fin.

Megalamphodus sweglesi is found in Colombia and Venezuela in the Orinoco basin. It is typically found in clear or tannin-stained water with high visibility, frequently among submerged aquatic plants, in both streams and lentic waters.

Megalamphodus sweglesi is classified in the genus Megalamphodus, which is Greek and means "with spacious ways", a name coined by Carl H. Eigenmann which he gave no explanation for. It may be an allusion to the "very large" fontanels, the frontal bones being described as “entirely separate”', that is, with a space between them and the parietal bones. The specific name honours Kyle Swegle, an American fish trader who collected the holotype.