Penion fairfieldae (Powell, 1947)[1] Penion chathamensis is a species of very large predatory sea snail or whelk, a marine gastropod mollusc in the family Austrosiphonidae.

[3] Although P. chathamensis has separate sexes, the species does not appear to exhibit secondary sexual dimorphism in shell shape or size.

[4] A separate species, Penion fairfieldae was formerly recognised, but recent genetic data has demonstrated that the species is indistinguishable from Penion chathamensis.

[1] Penion chathamensis is endemic to New Zealand.

[3][4][5] The species is distributed off of the west coast of the South Island, and occurs on Chatham Rise and in waters surrounding the Chatham Islands[3][4][5] The latter location is the type locality, giving rise to the binomial name of the species.