Key to the Superfamilies
1. Hinge with taxodont dentition (reduced
to a few teeth in some) > 2
Hinge edentate or with other than taxodont dentition > 9
2. Ligament internal > 3
Ligament mostly or entirely external > 6
3. Hinge teeth few in number, entirely or
mostly on one side of beaks > 4
Hinge teeth more than 8 and on both sides of beaks > 5
4. Hinge teeth about 5, on one side of beaks
only > Manzanelloidea
Hinge teeth 1 - 8, on both sides of beaks, more posteriorly > Pristiglomoidea
5. Shell very iridescent internally > Nucloidea
Shell porcelaneous (or slightly iridescent) > Nuculanoidea (in part)
6. Sculpture commarginal, not crenulate within
> Nuculanoidea (in part)
Sculpture radial and/or crenulate within > 7
7. Ligament in a triangular pit under beaks
> Limopsoidea
Ligament in chevron-shaped grooves > 8
8. Shape subquadrate, globose or elliptical
> Arcoidea
Shell ovate, not globose or elongate > Glycymeroidea
9. Dorsal margin produced anteriorly and posteriorly
into traiangular ears, or ligament in a series of pits > 10
Dorsal margin not produced into ears; ligament not divided into a series of
pits > 12
10. Shape alate or spatulate > Pterioidea
Shape other than alate or spatulate > 12
11. Shell much higher than long; ears small
> Limoidea
Shell height and length more or less similar; one or both ears large > Pectinoidea
12. With a large subcentral adductor muscle
scar > 13
With anterior and posterior muscle scars > 16
13. Shell triangonal > 14
Shell various, but not triangonal > 15
14. Shell large (to 360 mm), not hirsute
> Pinnoidea
Shell minute (<8 mm), hirsute > Philobryoidea
15. Adductor scar complex; central area showing two or more scars > Anomioidea
Adductor scar simple, with one central scar > Ostreoidea
16. Hinge simple, without conspicuous interlocking cardinal teeth, projecting
chondrophores, or myophores (may have inconspicuous denticles or a resilifer
on hinge plate, or left valve may fit into lateral grooves in right valve) >
17
Hinge complex, with two or more interlocking cardinal teeth in at least one
valve (may also have a chondrophore) > 34
Hinge complex, without interlocking cardinal teeth or a chondrophore, but with
projecting apophysis > Pholadoidea (most)
17. Adductor muscle very unequal in size; anterior scar smaller, near beaks;
beaks anterior in most > Mytiloidea
Adductor muscle scars of approximately same size; beaks not anterior > 18
18. Periostracum produced well beyond shell margin > Solemyoidea
Periostracum, if conspicuous, not produced well beyond shell margin > 19
19. Right valve cemented to substratum > Dimyoidea
Animal not cemented to substratum > 20
20. Shell porcelaneous within > 21
Shell nacreous within > 29
21. Shell rudimentary, without a true hinge > Galeommatoidea (some)
Shell normal; valves connected by a hinge > 22
22. Valves closing tightly > 23
Shell gaping ventrally or anteriorly > 28
23. With a conspicuous pallial sinus > Thracioidea (part)
Without a pallial sinus > 24
24. With conspicuous radial ribs, mostly on posterior end > Cuspidarioidea
Radial ribs absent or feeble > 25
25. Ligament external > 26
Ligament internal under beaks > 27
26. Ligament large, bulbous > Cardioidea (Serripes)
Ligament sunken into hinge plate > Lucinoidea (Thyasiridae)
27. Sculpture of conspicuous commarginal ribs > Myoiudea (Spheniopsidae)
Surface smooth Cuspidarioidea (part)
28. Pallial line continuous and with a deep sinus > Gastrochaenoidea
Pallial line disjunct and/or with shallow sinus > Hiatelloidea
29. Internal dorsal surface with crurae > Pandoroidea (Pandoridae)
Without crurae > 30
30. Sculpture of heavy radial ribs > Verticordioidea
Sculpture not of heavy radial ribs > 31
31. Ligament sunken on hinge plate > Poromyoidea
Ligament in an internal resilifer > 32
32. Shell with radial threads > 33
Shell smooth or with conventric lamellae, lacking radial threads > Pandoroidea
(Entodesma, Mytilimeria)
33. Shell ovate, or subquadrate with terminal beaks > Verticordioidea
(part)
Shell subquadrate to elliptical, without terminal beaks > Pandoroidea
(Lyonsia)
34. Shell cemented to substratum by one valve > Chamoidea
Shell not cemented > 35
35. Shell cylindrical, gaping at ends > 36
Shell not cylindrical > 37
36. Shell approximately equilateral; without internal reinforcing rib > Tellinoidea
(Solecurtidae)
Beaks at or near anterior end; without internal reinforcing rib > Solenoidea
(Solen, Ensis)
Beaks not at anterior end; with internal reinforcing rib > Solenoidea
(Siliqua)
37. Shell with radial ribs over most of surface, showing as crenulations within
(reduced in some to internal crenulations only) > 38
Sculpture absend, commarginal, cancellate, or only weakly radial > 40
38. Shell subquadrate > Carditoidea (Glans, Mineria)
Shell ovate > 39
39. Shell with anterior and posterior lateral teeth > 58
Shell without lateral teeth, or with only an anterior lateral > Carditoidea
(Cyclocardia,
Miodontiscus)
40. Shell with entirely or partially internal ligament > 41
Shell with entirely external ligament > 46
41. Pallial sinsus present > 42
Pallial sinus absent > 43
42. Hinge with two simple, small cardinal teeth in each valve > Tellinoidea
(Semelidae)
Hinge with a inverted V-shaped cardinal in each valve > Mactroidea
43. Ligament deeply internal and opisthodetic > 44
Ligament in resilifer directly below umbones > 45
44. Hinge plate thin; ligament elongate, completely internal, opisthodetic
> Galeommathoidea (part)
Hinge plate heavy, with short ligament sunken into it posteriorly > Cyamioidea
45. With heacy commarginal sculpture (sometimes confined to beaks) > Crassatelloidea
With commarginal striae or fine ribs only > Galeommatoidea (part)
46. Shell with a conspicuous pallial sinus > 47
Shell pallial sunus absent or very shallow > 48
47. Hinge with three cardinal teeth one or both valves > Veneroidea
(most)
Hinge with two teeth in each valve > Tellinoidea (most)
48. Anterior adductor muscle scar narrower than posterior, its lower end detached
from pallial line > Lucinoidea (most)
Anterior adductor muscle scars more or less equal in shape, not detached from
pallial line > 49
49. Hinge complex, with some cardinal teeth placed dorsal to others > Glossoidea
Cardinal teeth radial > 50
50. With three cardinal teeth in one or both valves > 51
With fewer than three in each valve > 52
51. With three cardinal teeth in each valve > Veneroidea (Chione)
With three cardinal teeth in right valve, two in the left > Corbiculoidea
With two cardinal teeth in each valve (sometimes obscure) > Cardioidea
(Serripes)
52. With one cardinal tooth in right valve, two in left valve > 53
With two cardinal teeth in each valve > 54
53. Hinge teeth very thick > Astartoidea
Hinge teeth minute > Veneroidea (Turtonidae)
54. Hinge with anterior and posterior laterals > Lucinoidea (Parvilucina)
Hinge lacking laterals or with only posterior lateral teeth > Arcticoidea
55. Hinge with a horizontally porjecting chondrophore in left valve and a socket
in right valve > Myoidea (most)
Hinge endentulous, or with ventrally projecting chondrophore in both valves
> 56
56. Shell gaping anteriorly, boring into substratum > Pholaadoidea
(Netastoma)
Shell not gaping anteriorly > 57
57. External surface pustulose > Thracioidea
External surface without pustules > Myoidea (Sphenia)
58. Cardinal teeth small, tubercular > Lucinoidea (Parvilucina)
Cardinal teeth projecting > Cardiodea