Original description as Haplochromis longimanus:
- Trewavas, Ethelwynn. 1935. "A Synopsis of the Cichlid Fishes of Lake Nyasa". Annals and Magazine of Natural History. Series 10; pp. 65-118 (crc00118)
Conservation: Placidochromis longimanus is evaluated by the international union for the conservation of nature in the iucn red list of threatened species as (LC) least concern (2018).