Trigonulina novemcostata is a carnivorous bivalve in the family Verticordiidae.

[1] It is native to the South China Sea with 7–8 prominent ribs on its surface[2] and ranges from about 0.7-5 millimeters in size[3] in accordance with the unaccepted genus Hippagus it was originally described as.

It is the only currently known species in the genus Trigonulina that lives outside of the western Atlantic Ocean,[4] being found in the South China Sea[1] and Pacific Ocean.

This species has been observed between California and Peru[5] as well as in Costa Rica.

[6] Malacologists currently debate if T. novemcostata is a separate species or a variant of T. ornata due to their similar appearances and habitat overlap.