Magnapinna sp. C is an undescribed species of bigfin squid known only from a single specimen of 79mm mantle length (ML) collected in the southern Atlantic Ocean and held in the Natural History Museum.
It is characterised by several morphological features: the proximal tentacles are more slender than arm pair IV, pigmentation is contained in the chromatophores, and "white nodules" are absent from the fins and glandular regions of the proximal tentacles.
Magnapinna sp. C was originally illustrated in The Open Sea in 1956 and identified as Octopodoteuthopsis.