Schizodus obscurus, from here.

Belongs within: Bivalvia.
Contains: Actinodontoida, Unionidae, Margaritiferidae, Trigoniidae, Myophoriidae, Mutelidae.

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. Fossil palaeoheterodontans include the Carboniferous Anthracosiidae which are common fossils in coal measures and would have inhabited brackish marshes. Babinka prima, from the Middle Ordovician of Czechia, 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.

<==Palaeoheterodonta [Naiadacea] GW02
    |  i. s.: Glyptarca Hicks 1873 C96
    |           `--G. primaeva Hicks 1873 SB93
    |--+--Actinodontoida C96
    |  `--Babinka [Babinkidae, Babinkoidea] M96
    |       `--B. prima Barrande 1881 SB93
    `--+--+--Unionoida [Naiadacea] G07
       |  |    |--Unionidae GW02
       |  |    `--Margaritiferidae G07
       |  `--Anthracosiidae [Anthrocosioidea] M96
       |       |--Naiadites fragilis (Meek & Worthen 1866) SB93
       |       |--Palaenodonta castor (Eichwald 1856) SB93
       |       |--Anthracosia ladina G31
       |       |--Anthracomya SB93
       |       |    |--A. laevis G31
       |       |    |--A. minima G31
       |       |    |--A. modiomorphoides G31
       |       |    |--A. ovalis (Dawson 1860) SB93
       |       |    |--A. phillipsi G31
       |       |    `--A. wardiformis G31
       |       `--Carbonicola SB93
       |            |--C. bradorica (Dawson 1868) SB93
       |            |--C. carbonaria G31
       |            |--C. ovalis G31
       |            |--C. subrotunda G31
       |            |--C. virti G31
       |            `--C. wangsoweni G31
       `--Trigonioida [Trigoniacea, Trigoniina, Trigonoidea] GW02
            |  i. s.: Cytherodon SB93
            |         Hefteria SB93
            |         Liotrigonia SB93
            |         Rhenania SB93
            |         Toechomya SB93
            |         Nipponotrigonia SB93
            |--Trigoniidae M96
            |--Myophoriidae F99
            |--Mutelidae SB93
            |--Eoschizodus [Eoschizodiidae] SB93
            |    `--E. truncatus (Goldfuss 1837) SB93
            |--Scaphellina [Scaphellinidae] SB93
            |    `--S. concinnus (Branson 1930) SB93
            |--Eoastartidae SB93
            |    |--Eoastarte subcircularis Ciriacks 1963 SB93
            |    `--Kaibabella (Flattopia) axinia Waterhouse 1987 SB93
            |--Actinodontophoridae SB93
            |    |--Actinodontophora katsurensis Ichikawa 1951 SB93
            |    `--Palaeopharus elongatus Moore 1861 SB93
            |--Pachycardiidae [Trigonodidae] SB93
            |    |--Pachycardia rugosa Hauer 1857 SB93
            |    |--Trigonodus sandbergeri (Stoliczka 1871) SB93
            |    |--Cardinioides varidus Hayami 1957 SB93
            |    `--Kidodia SB93
            |--Trigonioididae [Trigonioidacea] SB93
            |    |--Plicatounio K84
            |    |--Nippononaia asinaria Reeside 1957 K84, G88
            |    `--Trigonioides K84
            |         |--T. kobayashi (Hoffet 1937) SB93
            |         `--T. kodairai Kobayashi & Suzuki 1936 SB93
            |--Etheriidae SB93
            |    |--Acostaea [incl. Eumulleria Anthony 1907, Mulleria Férussac 1823] PB27
            |    |--Pseudomulleria PB27
            |    |--Bartlettia Adams 1866 A66
            |    |    `--*B. stefanensis (Moricand 1856) [=Etheria stefanensis] A66
            |    `--Etheria Lamarck 1807 (see below for synonymy) PB27
            |         |--*E. semilunata Lamarck 1807 PB27, SB93 [=Aetheria semilunata PB27, E. semilunaris (l. c.) PB27]
            |         `--E. elliptica Lamarck 1807 (see below for synonymy) PB27
            `--Schizodus King 1844 W77 [Schizodiidae SB93]
                 |--*S. truncatus G31
                 |--S. compressus G31
                 |--S. delicatula (Fletcher 1929) [=Astartila delicatula] F71
                 |--S. dubiformis G31
                 |--S. elongatus Grabau 1931 G31
                 |--S. kennedyensis Dickins 1956 F71
                 |--S. obscurus Sowerby 1821 W77
                 |--S. pinguis G31
                 |--S. rossicus G31
                 |--S. subcarinata (Fletcher 1929) [=Astartila subcarinata] F71
                 |--S. subquadratus Grabau 1931 G31
                 `--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


[A66] Adams, H. 1866. List of land and freshwater shells collected by Mr. E. Bartlett on the Upper Amazons, and on the River Ucayali, eastern Peru, with descriptions of new species. Proceedings of the Zoological Society of London 1866: 440–445.

[C96] Cope, J. C. W. 1996. The early evolution of the Bivalvia. In: Taylor, J. D. (ed.) Origin and Evolutionary Radiation of the Mollusca pp. 361–370. Oxford University Press: Oxford.

[F71] Fletcher, H. O. 1971. Catalogue of type specimens of fossils in the Australian Museum, Sydney. Australian Museum Memoir 13: 1–167.

[F99] Freneix, S. 1999. Bivalves du Trias tariquide de Los Pastores (Algésiras), Espagne. Leur signification. Geodiversitas 21 (2): 137–146.

[GW02] Giribet, G., & W. Wheeler. 2002. On bivalve phylogeny: a high-level analysis of the Bivalvia (Mollusca) based on combined morphology and DNA sequence data. Invertebrate Biology 121 (4): 271–324.

[G31] Grabau, A. W. 1931. The Permian of Mongolia: A report on the Permian fauna of the Jisu Honguer limestone of Mongolia and its relations to the Permian of other parts of the world. American Museum of Natural History: New York.

[G07] Graf, D. L. 2007. Palaearctic freshwater mussel (Mollusca: Bivalvia: Unionoida) diversity and the Comparatory Method as a species concept. Proceedings of the Academy of Natural Sciences of Philadelphia 156: 71–88.

[G88] Gray, J. 1988. Evolution of the freshwater ecosystem: the fossil record. Palaeogeography, Palaeoclimatology, Palaeoecology 62: 1–214.

[K84] Kobayashi, T. 1984. On the non-marine Mesozoic faunas of Asia and their bearing on the historical geology. Fossils 35: 33–37.

[M96] Morton, B. 1996. The evolutionary history of the Bivalvia. In: Taylor, J. D. (ed.) Origin and Evolutionary Radiation of the Mollusca pp. 337–359. Oxford University Press: Oxford.

[PB27] Pilsbry, H. A., & J. Bequaert. 1927. The aquatic mollusks of the Belgian Congo, with a geographical and ecological account of Congo malacology. Bulletin of the American Museum of Natural History 53 (2): 69–602, pls 10–77.

[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.

Last updated: 6 March 2022.

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