Penion mandarinus, common name the mandarin penion, southern siphon whelk or Waite's buccinum whelk, is a species of medium-to-large predatory sea snail or whelk, a marine gastropod mollusc in the family Austrosiphonidae.

[10][11] Penion mandarinus is a medium-to-large sized species of siphon whelk.

[12][13] The species could be confused with the sympatric species P. maximus, however P. mandarinus is typically smaller and has a smoother shell with a shorter siphonal canal.

[12][13][14] Penion mandarinus is closely related to another Australian species P.

[13][15] The species have overlapping geographic ranges (sympatry) and may have evolved from a common ancestor via niche differentiation based on prey size and water depth.