Trigonulina is a genus of small carnivorous bivalves in the family Verticordiidae.

[1][2] It was first named by Alcide d'Orbigny with the type taxon T. ornata in 1853, though T. novemcostata was named first originally as Hippagus novemcostatus in 1850 which is now unaccepted.

[3] Trigonulina shells are known to be extremely small, ranging from about 1-3.6 millimeters long.

[2] They live at depths of 18-850 meters below the ocean's surface and burrow under sand to feed on microscopic crustaceans using adapted inhalant siphons.

[2] T. ornata lives in the western Atlantic Ocean[2] while T. novemcostata is native to the South China Sea.