Key:  Order Nuculoida

Taken primarily from  Kozloff, 1987, 1996 p. 266 (Copyright 1987, 1996, University of Washington Press.  Used in this web page by permission of University of Washington Press)

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Lower taxonomic level	Main Page	Alphabetic Index	Systematic Index	Glossary

1a	Ligament external; interior of valves porcellanous, not pearly; with a pallial sinus (animal with siphons)	2
1b	Ligament internal (photo); interior of valves pearly, especially when fresh; without a pallial sinus	Family Nuculidae
2a	With a chondrophore on the lower part of the hinge plate	3
2b	Without a chondrophore	4
3a	Shell closing tightly, pallial sinus shallow	Family Nuculanidae
3b	Shell gaping posteriorly; pallial sinus deep	Family Yoldiidae
4a	Series of hinge teeth posterior to the umbo nearly twice as long as the series anterior to the umbo; posterior ends of valves rounded	Family Malletiidae
4b	Series of hinge teeth posterior to the umbo not much longer than the series anterior to the umbo; posterior ends of valves somewhat pointed due to way the the curved ventral margin meets the nearly straight dorsal margin	Family Tindariidae

  Family Nuculidae
  Family Yoldiidae