Diversity of Extant Bivalves
The adult maximum size of living species of bivalve ranges from 0.52 mm (0.02 in) in Condylonucula maya, a nut clam, to a length of 1,532 millimetres (60.3 in) in Kuphus polythalamia, an elongated, burrowing shipworm. However, the species generally regarded as the largest living bivalve is the giant clam Tridacna gigas, which can grow to a length of 1,200 millimetres (47 in) and a weight of more than 200 kilograms (441 lbs). The largest known extinct bivalve is a species of Platyceramus whose fossils measure up to 3,000 mm (118 in) in length.
In his 2010 treatise, Compendium of Bivalves, Markus Huber gives the total number of living bivalve species as about 9,200 combined in 106 families. Huber states that the number of 20,000 living species, often encountered in literature, could not be verified and presents the following table to illustrate the known diversity:
| Subclass | Order | Families | Genera | Species |
|---|---|---|---|---|
| Heterodonta | 64 (incl. 1 freshwater) | &0800800 (incl. 16 freshwater) | &56005600 (incl. 270 freshwater) | |
| Arcticoidea | 2 | &00066 | &001313 | |
| Cardioidea | 2 | &003838 | &0260260 | |
| Chamoidea | 1 | &00066 | &007070 | |
| Clavagelloidea | 1 | &00022 | &002020 | |
| Crassatelloidea | 5 | &006565 | &0420420 | |
| Cuspidarioidea | 2 | &002020 | &0320320 | |
| Cyamioidea | 3 | &002222 | &0140140 | |
| Cyrenoidea | 1 | &00066 (3 freshwater) | &006060 (30 freshwater) | |
| Cyrenoidoidea | 1 | &00011 | &00066 | |
| Dreissenoidea | 1 | &00033 (2 freshwater) | &002020 (12 freshwater) | |
| Galeommatoidea | 4 !ca. 4 | &0100ca. 100 | &0500ca. 500 | |
| Gastrochaenoidea | 1 | &00077 | &003030 | |
| Glossoidea | 2 | &002020 | &0110110 | |
| Hemidonacoidea | 1 | &00011 | &00066 | |
| Hiatelloidea | 1 | &00055 | &002525 | |
| Limoidea | 1 | &00088 | &0250250 | |
| Lucinoidea | 2 | &0085ca. 85 | &0500ca. 500 | |
| Mactroidea | 4 | &004646 | &0220220 | |
| Myoidea | 3 | &001515 (1 freshwater) | &0130130 (1 freshwater) | |
| Pandoroidea | 7 | &003030 | &0250250 | |
| Pholadoidea | 2 | &003434 (1 freshwater) | &0200200 (3 freshwater) | |
| Pholadomyoidea | 2 | &00033 | &002020 | |
| Solenoidea | 2 | &001717 (2 freshwater) | &0130130 (4 freshwater) | |
| Sphaerioidea | 1 !(1 freshwater) | &0005(5 freshwater) | &0200(200 freshwater) | |
| Tellinoidea | 5 | &0110110 (2 freshwater) | &0900900 (15 freshwater) | |
| Thyasiroidea | 1 | &0012ca. 12 | &0100ca. 100 | |
| Ungulinoidea | 1 | &001616 | &0100100 | |
| Veneroidea | 4 | &0104104 | &0750750 | |
| Verticordioidea | 2 | &001616 | &0160160 | |
| Palaeoheterodonta | 7 (incl. 6 freshwater) | &0171171 (incl. 170 freshwater) | &0908908 (incl. 900 freshwater) | |
| Trigonioidea | 1 | &00011 | &00088 | |
| Unionoidea | 6 !(6 freshwater) | &0170(170 freshwater) | &0900(900 freshwater) | |
| Protobranchia | 10 | &004949 | &0700700 | |
| Manzanelloidea | 1 | &00022 | &002020 | |
| Nuculanoidea | 6 | &003232 | &0460460 | |
| Nuculoidea | 1 | &00088 | &0170170 | |
| Sapretoidea | 1 | &0005ca. 5 | &001010 | |
| Solemyoidea | 1 | &00022 | &003030 | |
| Pteriomorpha | 25 | &0240240 (incl. 2 freshwater) | &20002000 (incl. 11 freshwater) | |
| Anomioidea | 2 | &00099 | &003030 | |
| Arcoidea | 7 | &006060 (1 freshwater) | &0570570 (6 freshwater) | |
| Dimyoidea | 1 | &00033 | &001515 | |
| Limoidea | 1 | &00088 | &0250250 | |
| Mytiloidea | 1 | &005050 (1 freshwater) | &0400400 (5 freshwater) | |
| Ostreoidea | 2 | &002323 | &008080 | |
| Pectinoidea | 4 | &006868 | &0500500 | |
| Pinnoidea | 1 | &00033 (+) | &005050 | |
| Plicatuloidea | 1 | &00011 | &002020 | |
| Pterioidea | 5 | &00099 | &008080 |
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