Phylum: Mollusca
Class: Bivalvia
Order: Trigonoida Dall, 1889
Cincinnatian Families: Lyrodesmatidae

Geologic Range
?Middle Ordovician, Devonian – Recent

Common Paleoecology
Trigonioda is an extant order or facultatively mobile infaunal suspension feeders

Characteristics of the Order

  • Shell trigonal, ovate, or rhomboidal in shape
  • Surface smooth or ornamented
  • Hinge teeth radiating from the beak; left valve with strong median tooth & right valve typically with two main teeth
  • Small adductor scars found close to hinge teeth

Published Descriptions

Treatise on Invertebrate Paleontology, Part N, Mollusca 6(1 of 3) (1969):

  • (Characters of superfamily Trigoniacea) Shell equivalve; trigonal, ovate or rhomboidal; posteriorly truncate or subtruncate; posterior slope carinate or subcarinate; surface smooth or ornamented; ligament external, short, opisthodetic. Hinge teeth radiating from beak; left valve typically with strong median tooth and weaker one on each side; right valve typically with two main teeth received in recesses between those of left; additional and weaker teeth may be present, however, or some of teeth mentioned may be obsolete; adductor scars small, placed close to hinge teeth, anterior scar in each valve bordered on its inner side in many forms by buttress may border posterior adductor scar; pallial line entire except in Scaphellinidae; ostracum nacreous.