Phenatoma decessor

Phenatoma decessor is an extinct species of sea snail, a marine gastropod mollusk in the family Borsoniidae.

Description
The length of the shell is 17 mm, its width 6 mm. Marwick considered this species a direct ancestor of Phenatoma rosea to which it closely resembles in shape and ornamentation.

Distribution
This extinct marine species was endemic to New Zealand and fossils were found in fossiliferous beds of calcareous tuffs at Whenuaturu Peninsula.