ID Keys
*Images in development

Major Taxa

Hinge taxodont [c1ab], some deep water with subparallel teeth [c1c]
Go to #2
Hinge not taxodont or lacking teeth
Go to #4
Ligament internal [c2] or as a small external arched band [c3]
Ligament external set on a flat [c4] or cleft [c5] dorsal area
Go to #3
Duplivincular (many bands) [c6a,b,c], Outline trapezoidal to rhomboidal but if oval isomyarian [c7] = Arcoidea
Arcoida (Arcoidea & Limopsoidea)
Alivincular (simple triangular) [c8] Outline obliquely oval, heteromyarian [c9] = Limopsoidea
Arcoida (Arcoidea & Limopsoidea)
Shell thin, proteinaceous, greatly reduced anteriorly [c10,c11,c12}, byssate, lacking true hinge teeth, ligament external
Pterioida & Mytiloida
Shell typically calcareous, if reduced anteriorly then gaping or with true teeth, free-living, cemented or weakly byssate, ligament external or internal
Go to #5
One valve cemented to or conforming to the substrate, if latter then lower valve with a foramen [c13] through which the byssus passes
Ostreoidea, Chamoidea & Anomioidea
Shell not cemented or with lower valve with a byssus foramen
Go to #6
Shells discoid [c14] to oval [c15] with projections (ears) [c17] extending from at least one side of the umbos
Go to #7
Shells lacking "ears"
Go to #8
Shells discoid, ligament internal [c18]
Shells obliquely oval to oval, ligament external in a triangular depression between the beaks
Boring into rock, wood or peat within a fitting burrow
Rock and wood borers
Not boring into rock or wood but may nestle in old burrows and crevices
Go to #9
With at least 2 radiating cardinal teeth in each valve, ligament external or partly internal on a chondrophore or wholly internal
Go to #10
Hinge not with this combination of characters
Go to #16
Pallial line entire
Go to #11
Pallial sinus present, in some represented only by a slightly indentation of the posterior ventral line if so lateral tooth present
Go to #14
Hinge with 2 cardinals and anterior and posterior laterals, most with radial ribbing
Not this
Go to #12
Anterior adductor scar elongate, posterior oval
Veneroidea and venerid-like clams
Adductor scars of similar shape and size
Go to #13
Heavy hinge, 1-3 cardinal teeth, commarginal lines/ridges
Hinge with 3 cardinal teeth and posterior laterals
Veneroidea and venerid-like clams
Both valves with 2 cardinals, laterals absent or present, some with partly internal ligament on chondrophore, cruciform muscle scars present, pallial sinus extensive
Not this combination
Go to #15
Ligament external, 3 cardinals in LV 2 or 3 in RV, laterals absent or present
Veneroidea and venerid-like clams
Ligament mostly internal in a shallow but wide resilifer, most have LV with inverted v-shaped cardinal teeth
Ligament external or partly external, visible along the dorsal margin of joined valves
Go to #17
Ligament internal on a shallow resilifer or projecting chondrophore
Go to #21
Elongate, cylindical shells, LV with 2 cardinals RV with 1
Subovate, polygonal or oblong shells
Go to #18
Hinge glossoid, cardinal teeth subparallel with hinge line
Veneroidea and venerid-like clams
Cardinal teeth reduced or absent
Go to #19
Thin, subovate to polygonal shells, ligament external but sunken, teeth absent or poorly formed
Oblong, subovate to rhomboidal shells
Go to #20
Oblong to subovate shells, ligament partly internal on a shallow projecting resilifer, teeth absent, many pustulose
Oblong to rhomboidal in outline ligament wholly external, teeth reduced or absent
Hiatelloidea & Basterotiidae
Shells with a distinct posterior extension, rostrate or subrostrate
Shells not rostrate
Go to #22
Hinge with a projecting, tooth-like, chondrophore in one valve, Corbiculidae very inequivalve
Chondrophore not projecting or if projecting then equally in both valves
Go to #23
Chondrophore projecting in both valves, umbonal stress fracture present
Chondrophore not projecting or not present
Go to #24
Shells markedly inequivalve
Shells not markedly inequivalve
Go to #25
Shells nacreous with or without a shallow chondrophore, ligament supported by a lithodesma, teeth rudimentary, mostly deep water species with some granular microsculpture.
Shells not nacreous ligament inserted on the hinge plate, or in the umbonal cavity or attached to a resilial shelf, mostly small shelf species, many commensal, shell lacking granular microsculpture