Thyasira motutaraensis is an extinct species of bivalve, a marine mollusc, in the family Thyasiridae. Fossils of the species date to early Miocene strata of the west coast of the Auckland Region, New Zealand.
In the original description, Powell described the species as follows:
The holotype of the species measures in height, in width, and has a thickness of when measuring both valves. The species can be differentiated from T. marwicki due to being higher than it is more, more angular when viewed from above, being almost equilateral, and by having an extra radial furrow bordering its lunule, and from T. bartrumi due to its having a less lunule and by having a furrow border.
The species was first described by A. W. B. Powell in 1935 as Thyasira (Prothyasira) motutaraensis. Its currently accepted name is Thyasira motutaraensis, without a subgenus. The holotype was collected at an unknown date prior to 1935 from between Powell Bay and Bartrum Bay, approximately south of Muriwai, Auckland Region (then more commonly known as Motutara), and is held in the collections of Auckland War Memorial Museum.
This extinct marine species occurs in early Miocene strata of the Nihotupu Formation of New Zealand, on the west coast of the WaitÃÂkere Ranges of the Auckland Region, New Zealand. The Powell Bay site deposits of the Nihotupu Formation in the western WaitÃÂkere Ranges are mid-bathyal .