Belongs within: Bivalvia.
Contains: Actinodontoida, Unionidae, Margaritiferidae, Mutelidae, Anthracosiidae, Trigoniidae, Myophoriidae.
The Palaeoheterodonta is a clade of bivalves represented in the modern fauna by two quite divergent subclades, the angular-shelled Neotrigonia (sole surviving lineage of the Trigonioida) and the freshwater clams of the Unionoida. Though the integrity of the Palaeoheterodonta has been questioned in the past, monophyly of the living members is supported by molecular analysis (Giribet & Wheeler 2002). The Trigonioida have a distinctive posteriorly truncate shell shape with a carinate or subcarinate posterior slope, and are marine. Unionoida are mostly found in flowing waters such as rivers and streams; they disperse upstream by means of larvae called glochidia that attach to the gills of fish before falling off and settling as mature clams. Unionoidans may be divided between the Unionoidea, which typically have well-developed to heavy cardinal teeth, and the Muteloidea, in which the hinge is more or less edentulous (Beesley et al. 1998).
Fossil palaeoheterodontans include Babinka prima from the Middle Ordovician of Czechia, which has an anteriorly expanded, compressed shell with two small cardinal teeth in the left valve and one large cardinal tooth in the right valve. The Trigonioida have an extensive fossil record extending to the Devonian. Schizodus is a trigonioid genus of smooth-shelled species with the left valve hinge containing a strong, bilobed median tooth, small and marginal anterior tooth, and a mostly or entirely obsolete posterior tooth.
<==Palaeoheterodonta [Naiadacea]GW02
| i. s.: Glyptarca Hicks 1873C96
| `--G. primaeva Hicks 1873SB93
|--+--ActinodontoidaC96
| `--Babinka [Babinkidae, Babinkoidea]M96
| `--B. prima Barrande 1881SB93
`--+--+--Unionoida [Naiadacea, Naiades]G07
| | |--UnionoideaBRW98
| | | |--UnionidaeSS97
| | | `--MargaritiferidaeG07
| | `--MuteloideaBRW98
| | |--MutelidaeSB93
| | |--MycetopusA66 [Mycetopinae, MycetopodidaeBRW98]
| | | `--M. soleniformisA66
| | `--EtheriidaeBRW98
| | |--Acostaea [incl. Eumulleria Anthony 1907, Mulleria Férussac 1823]PB27
| | |--PseudomulleriaPB27
| | |--Bartlettia Adams 1866A66
| | | `--*B. stefanensis (Moricand 1856) [=Etheria stefanensis]A66
| | `--Etheria Lamarck 1807 (see below for synonymy)PB27
| | |--*E. semilunata Lamarck 1807PB27, SB93 [=Aetheria semilunataPB27, E. semilunaris (l. c.)PB27]
| | `--E. elliptica Lamarck 1807 (see below for synonymy)PB27
| `--AnthracosiidaeM96
`--Trigonioida [Trigoniacea, Trigoniina, Trigonoidea]GW02
| i. s.: CytherodonSB93
| HefteriaSB93
| LiotrigoniaSB93
| RhenaniaSB93
| ToechomyaSB93
| NipponotrigoniaSB93
|--TrigoniidaeM96
|--MyophoriidaeF99
|--Scaphellina [Scaphellinidae]SB93
| `--S. concinnus (Branson 1930)SB93
|--Eoschizodus [Eoschizodiidae]SB93
| |--E. taemasensisBRW98
| `--E. truncatus (Goldfuss 1837)SB93
|--EoastartidaeSB93
| |--Eoastarte subcircularis Ciriacks 1963SB93
| `--Kaibabella (Flattopia) axinia Waterhouse 1987SB93
|--ActinodontophoridaeSB93
| |--ActinodontophoraSB93
| | |--A. katsurensis Ichikawa 1951SB93
| | `--A. qinglongensisX89
| `--Palaeopharus elongatus Moore 1861SB93
|--Pachycardiidae [Trigonodidae]SB93
| |--Pachycardia rugosa Hauer 1857SB93
| |--Trigonodus sandbergeri (Stoliczka 1871)SB93
| |--Cardinioides varidus Hayami 1957SB93
| `--KidodiaSB93
|--Trigonioididae [Trigonioidacea]SB93
| |--PlicatounioK84
| |--Nippononaia asinaria Reeside 1957K84, G88
| `--TrigonioidesK84
| |--T. kobayashi (Hoffet 1937)SB93
| `--T. kodairai Kobayashi & Suzuki 1936SB93
`--Schizodus King 1844W77 [SchizodiidaeSB93]
|--*S. truncatusG31
|--S. compressusG31
|--S. delicatula (Fletcher 1929) [=Astartila delicatula]F71
|--S. dubiformisG31
|--S. elongatus Grabau 1931G31
|--S. kennedyensis Dickins 1956F71
|--S. obscurus Sowerby 1821W77
|--S. pinguisG31
|--S. rossicusG31
|--S. subcarinata (Fletcher 1929) [=Astartila subcarinata]F71
|--S. subquadratus Grabau 1931G31
`--S. wheeleri (Swallow 1862) [=Cypricardia wheeleri]W77
Etheria Lamarck 1807 [=Aetheria Berthold 1827, Etherea Schweigger 1820; incl. Caillaudiana Bourguignat 1880–1881, Chambardiana Bourguignat 1880–1881, Letourneuxiana Bourguignat 1880–1881, Niloticiana Bourguignat 1880–1881]PB27
Etheria elliptica Lamarck 1807 [=Aetheria (*Niloticiana) elliptica, A. elliptica var. typica Germain in Anthony 1907; incl. A. bourguignati de Rochebrune 1886, A. elliptica var. bourguignati, Etheria cailliaudi Férussac 1823, A. (*Caillaudiana) caillaudi, E. caillaudi, E. carteroni Michelin 1830, Aetheria (*Chambardiana) chambardi Bourguignat 1880–1881, A. denhami Koenig 1826, A. elliptica f. globosa v. Martens 1897, A. heteromorpha Simroth 1894, Etheria lamarckii Férussac 1823, A. letourneuxi Bourguignat 1880–1881, A. nidushirundinis Simroth 1890, A. heteromorpha mut. nidushirundinis, A. nilotica Letourneux in Bourguignat 1880–1881, Etheria plumbea Férussac 1823, Aetheria plumbea, E. plombea (l. c.), A. (*Letourneuxiana) petrettinii Bourguignat 1880–1881, A. cailliaudi var. rotundata Sowerby 1825 (n. n.), A. senegalica Bourguignat 1880–1881, A. tanganikana Bourguignat 1889, Etheria transversa Lamarck 1807, E. trigonula Lamarck 1807, Aetheria elliptica var. trigonula, E. tubifera Sowerby 1825, A. elliptica var. tubifera, A. heteromorpha mut. tubulifera Simroth 1894, A. tubulosa Bk. in Simroth 1894]PB27
*Type species of generic name indicated
References
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[SS97] Schloesser, D. W., R. D. Smithee, G. D. Longton & W. P. Kovalak. 1997. Zebra mussel induced mortality of unionids in firm substrata of western Lake Erie and a habitat for survival. American Malacological Bulletin 14 (1): 67–74.
[SB93] Skelton, P. W., & M. J. Benton. 1993. Mollusca: Rostroconchia, Scaphopoda and Bivalvia. In: Benton, M. J. (ed.) The Fossil Record 2 pp. 237–263. Chapman & Hall: London.
[W77] White, C. A. 1877. Report upon the invertebrate fossils collected in portions of Nevada, Utah, Colorado, New Mexico, and Arizona, by parties of the expeditions of 1871, 1872, 1873, and 1874. U.S. Geographical Surveys West of the One Hundredth Meridian 4 (1): 1–219, pls 1–21.
[X89] Xi Y.-H. 1989. Late Permian–Early Triassic Gastropods from Zhongying, Qinglong of Guizhou with analysis of their feeding habits and forms. Acta Palaeontologica Sinica 28 (5): 683–686.