Barythaerus biconvexus

Barythaerus biconvexus is a marine bivalve mollusc of the family Thraciidae. It is endemic to New Zealand, with records off southern South Island and Stewart Island.

Barythaerus biconvexus measures up to 5.1 mm in length. It is known from depths between 27-311 m, with live specimens from bryozoan and shell substrates at intermediate depths (55–183 m).