Ohio pigtoe Pleurobema cordatum, from the Illinois State Museum.

Belongs within: Bivalvia.
Contains: Trigoniidae, Myophoriidae, Mutelidae, Hyriidae, Anodonta, Unio, Lampsilis, Quadrula.

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. 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. 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 Cambrian to Devonian Cycloconchoidea, which have hinges with elongate teeth lacking denticles, or reduced dentition, may represent early members of this lineage.

Characters (from Cox et al. 1969): Equivalve, with closed margins and prismatonacreous shells; ligament amphidetic or opisthodetic, external and parivincular; dentition generally consisting of few teeth more or less radial and divergent from umbonal region, striated in some genera, rarely becoming taxodont in few genera (certain Unionoida); where lateral teeth occur, they originate below beaks and are not separated from cardinals
by edentulous interval.

    |--Trigonioida [Trigoniacea, Trigoniina, Trigonoidea] GW02
    |    |--Trigoniidae GW02
    |    `--Myophoriidae F99
    |--Cycloconchoidea [Actinodontoida] SV03
    |    |--Redoniidae SV03
    |    |--Intihuarella Sánchez & Vaccari 2003 [Intihuarellidae] SV03
    |    |    `--*I. simplicidentata Sánchez & Vaccari 2003 SV03
    |    `--Cycloconchidae SV03
    |         |--Fortowensia SV03
    |         |--Famatinadonta SV03
    |         `--Actinodonta G88
    `--Unionoida G88
         |  i. s.: Archanodon [Archanodontidae] G88
         |--Trigonioidacea G88
         |    |  i. s.: ‘Diplodon’ gregoryi G88
         |    |         ‘Diplodon’ haroldi G88
         |    `--Trigonioididae K84
         |           |--Trigonioides K84
         |           |--Plicatounio K84
         |           `--Nippononaia asinaria Reeside 1957 K84, G88
         |--Mutelacea G88
         |    |--Mutelidae G88
         |    `--Mycetopodidae G88
         |         |--Mycetopus soleniformis A66b
         |         |--Anodontites laciranus G88
         |         |--Mycetopoda diluculi Pilsbry in Wanner 1921 G88
         |         |--Etheria [Etheriidae] G88
         |         |    `--E. elliptica G88
         |         `--Monocondylaea G88
         |              |--M. (Plagiodon) isocardioides A66a
         |              `--M. marshalliana G88
         `--Unionoidea [Unionacea] GW02
              |--Hyriidae KJ13
              |--Margaritiferidae S88
              |    |--Cumberlandia monodonta S88
              |    `--Margaritifera S88
              |         |--M. auricularia S88
              |         |--M. hembeli (Conrad 1838) S88
              |         |--M. laosensis S88
              |         |--M. margaritifera S88
              |         `--M. marrianae S88
              `--Unionidae JN90
                   |--Psilunio littoralis GW02
                   |--Pseudodon inoscularis (Gould 1843) [=Anodonta inoscularis; incl. Monocondylaea vondembuschii] TC89
                   |--Anodonta JN90
                   |--Unio UM02
                   |--Actinonaias ligamentina (Lamarck 1819) JN90
                   |--Cyclonaias tuberculata (Rafinesque 1820) JN90
                   |--Tritogonia verrucosa (Rafinesque 1820) JN90 (see below for synonymy)
                   |--Lampsilis JN90
                   |--Cyprogenia OE97
                   |    |--C. aberti (Conrad 1850) OE97
                   |    `--C. stegaria (Rafinesque 1820) (see below for synonymy) V16
                   |--Amblema plicata (Say 1817) OE97
                   |--Venustaconcha ellipsiformis (Conrad 1836) OE97
                   |--Ellipsaria lineolata (Rafinesque 1820) OE97
                   |--Megalonaias nervosa (Rafinesque 1820) OE97
                   |--Leptodea fragilis (Rafinesque 1820) OE97
                   |--Obliquaria reflexa Rafinesque 1820 OE97 [=Unio reflexa V16]
                   |--Strophitus undulatus (Say 1817) OE97
                   |--Uniomerus tetralasmus (Say 1831) OE97
                   |--Utterbackia Baker 1927 OE97
                   |    `--U. imbecillis (Say 1829) OE97
                   |--Pyganodon Crosse & Fischer 1893 OE97
                   |    `--P. grandis (Say 1829) OE97
                   |--Alasmidonta OE97
                   |    |--A. marginata Say 1818 JN90
                   |    `--A. viridis (Rafinesque 1820) OE97
                   |--Villosa JN90
                   |    |--V. iris (Lea 1829) JN90
                   |    `--V. trabilis [=Micromya trabilis] USDI77
                   |--Truncilla OE97
                   |    |--T. brevidens Lea 1834 (see below for synonymy) V16
                   |    |--T. donaciformis (Lea 1827) OE97
                   |    |--T. flexuosa (Rafinesque 1820) [=Obliquaria flexuosa, Unio flexuosa] V16
                   |    |--T. obliqua (Rafinesque 1820) (see below for synonymy) V16
                   |    |--T. torulosa (Rafinesque 1820) (see below for synonymy) V16
                   |    |--T. triquetra Rafinesque 1820 [=T. triqueter, Unio triqueter] V16
                   |    `--T. truncata Rafinesque 1820 OE97 (see below for synonymy)
                   |--Ligumia OE97
                   |    |--L. recta (Lamarck 1819) OE97
                   |    `--L. subrostrata (Say 1831) OE97
                   |--Lasmigona JN90
                   |    |--L. complanata (Barnes 1823) OE97
                   |    |--L. costata (Rafinesque 1820) OE97
                   |    `--L. subviridis (Conrad 1835) JN90
                   |--Ptychobranchus OE97
                   |    |--P. fasciolaris (Rafinesque 1820) OE97 (see below for synonymy)
                   |    |--P. occidentalis (Conrad 1836) OE97
                   |    `--P. subtentum (Say 1825) OE97
                   |--Elliptio JN90
                   |    |--E. cistelliformis (Lea 1863) G97
                   |    |--E. complanata (Lightfoot 1786) OE97
                   |    |--E. dilatata (Rafinesque 1820) JN90 (see below for synonymy)
                   |    `--E. waccamawensis (Lea 1863) G97
                   |--Pleurobema PM89
                   |    |--P. beadleanum PM89
                   |    |--P. clava Lam. 1819 (see below for synonymy) V16
                   |    |--P. coccineum (Conrad 1834) OE97
                   |    |--P. conradi Vanatta 1916 [=Unio maculatus Conr. 1834 non U. maculata Rafinesque 1820] V16
                   |    |--P. cordatum (Rafinesque 1820) SS97
                   |    |--P. cyphia (Rafinesque 1820) (see below for synonymy) V16
                   |    |--P. plenum USDI77
                   |    `--P. simpsoni Vanatta 1916 [=Unio striatus Lea 1840 non Obovaria striata Rafinesque 1820] V16
                   |--Toxolasma JN90
                   |    |--T. cylindrella [=Carunculina cylindrella] USDI77
                   |    |--T. lividus (Rafinesque 1831) OE97
                   |    |--T. parvus (Barnes 1823) JN90
                   |    `--T. texasensis PM89
                   |--Potamilus OE97
                   |    |--P. alatus (Say 1817) SS97
                   |    |--P. caprax [=Proptera capax] USDI77
                   |    |--P. ohiensis (Rafinesque 1820) OE97
                   |    `--P. purpuratus (Lamarck 1819) OE97
                   |--Cucumerunio Iredale 1934 P61
                   |    |--*C. novaehollandiae [=Unio novaehollandiae] P61
                   |    `--C. websteri (Simpson 1902) P61
                   |         |--C. w. websteri P61
                   |         `--C. w. delli McMichael & Hiscock 1958 P61
                   |--Fusconaia WMP89
                   |    |--F. cuneolus USDI77
                   |    |--F. ebena (Lea 1831) WMP89
                   |    |--F. edgariana USDI77
                   |    |--F. flava (Rafinesque 1820) OE97
                   |    `--F. ozarkensis (Call 1887) OE97
                   |--Hyridella (Echyridella McMichael & Hiscock 1958) P61
                   |    `--H. (*E.) menziesi (Gray 1843) [=Unio menziesi] P61
                   |         |--H. m. menziesi [incl. H. lucasi, H. rugulosum, H. zelebori] P61
                   |         |--H. m. aucklandica (Gray 1843) [incl. H. lutulentus] P61
                   |         |--H. m. depauperata (Hutton 1883) [incl. H. acuta] P61
                   |         `--H. m. hochstetteri (Dunker 1862) P61
                   `--Quadrula JN90

Cyprogenia stegaria (Rafinesque 1820) [=Obovaria stegaria, Unio stegaria; incl. Cyprogenia irrorata Lea 1830, Obovaria stegaria var. tuberculata Rafinesque 1820 non Unio tuberculata Rafinesque 1820] V16

Elliptio dilatata (Rafinesque 1820) JN90 [=Unio dilatata V16; incl. U. gibbosus Bar. 1823 non Rafinesque 1820 V16, Obliquaria sinuata Rafinesque 1820 V16, U. sinuata V16]

Pleurobema clava Lam. 1819 [incl. P. cuneata Rafinesque 1820, Unio cuneata, U. elliptica Rafinesque 1820, Elliptio elliptica, Obliquaria scalenia Rafinesque 1820, Unio scalenia] V16

Pleurobema cyphia (Rafinesque 1820) [=Obliquaria cyphya, Unio cyphia; incl. Pleurobema aesopus Green 1827] V16

Ptychobranchus fasciolaris (Rafinesque 1820) OE97 [=Obliquaria fasciolaris V16, Unio fasciolaris V16; incl. Ptychobranchus phaseolus Hild. 1828 V16]

Tritogonia verrucosa (Rafinesque 1820) JN90 [=Obliquaria verrucosa V16, Unio verrucosa V16; incl. U. tuberculata Bar. 1823 nec Rafinesque 1820 nec Obovaria stegaria var. tuberculata Rafinesque 1820 V16, Tritogonia tuberculata V16]

Truncilla brevidens Lea 1834 [incl. Obliquaria interrupta Rafinesque 1820 non Unio solenoides interrupta Rafinesque 1820] V16

Truncilla obliqua (Rafinesque 1820) [=Obliquaria obliquata, Unio obliquata; incl. U. sulcatus Lea 1830 non U. cuneata var. sulcata Rafinesque 1820, Truncilla sulcata] V16

Truncilla torulosa (Rafinesque 1820) [=Amblema torulosa, Unio torulosa; incl. A. gibbosa Rafinesque 1820, U. gibbosa, Truncilla perplexa Lea 1831] V16

Truncilla truncata Rafinesque 1820 non Unio truncata Spengl. 1793 (not preoc. if in dif. gen.) OE97 [=Unio truncata V16]

*Type species of generic name indicated


[A66a] Adams, H. 1866a. 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.

[A66b] Adams, H. 1866b. Descriptions of six new species of shells, and note on Opisthostoma de-Crespignii. Proceedings of the Zoological Society of London 1866: 445–447.

Cox, L. R., N. D. Newell et al. 1969. Treatise on Invertebrate Paleontology pt N. Bivalvia vol. 1. The Geological Society of America, Inc. and The University of Kansas.

[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.

[G97] Graf, D. L. 1997. Sympatric speciation of freshwater mussels (Bivalvia: Unionoidea): a model. American Malacological Bulletin 14 (1): 35–40.

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

[JN90] Jirka, K. J. & R. J. Neves. 1990. Freshwater mussel fauna (Bivalvia: Unionidae) of the New River Gorge National River, West Virginia. Nautilus 103 (4): 136–139.

[KJ13] Klunzinger, M. W., H. A. Jones, J. Keleher & D. L. Morgan. 2013. A new record of Lortiella froggatti Iredale, 1934 (Bivalvia: Unionoida: Hyriidae) from the Pilbara region, Western Australia, with notes on anatomy and geographic range. Records of the Western Australian Museum 28 (1): 1–6.

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

[OE97] Obermeyer, B. K., D. R. Edds, C. W. Prophet & E. J. Miller. 1997. Freshwater mussels (Bivalvia: Unionidae) in the Verdigris, Neosho, and Spring River basins of Kansas and Missouri, with emphasis on species of concern. American Malacological Bulletin 14 (1): 41–55.

[PM89] Payne, B. S., A. C. Miller, P. D. Hartfield & R. F. McMahon. 1989. Variation in size demography of lotic populations of Corbicula fluminea (Müller). Nautilus 103 (2): 78–82.

[P61] Powell, A. W. B. 1961. Shells of New Zealand: An illustrated handbook 4th ed. Whitcombe and Tombs Limited: Christchurch.

[SV03] Sánchez, T. M., & N. E. Vaccari. 2003. Ucumariidae new family (Bivalvia, Anomalodesmata) and other bivalves from the Early Ordovician (Tremadocian) of northwestern Argentina. Ameghiniana 40 (3): 415–424.

[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.

[S88] Smith, D. G. 1988. Notes on the biology and morphology of Margaritifera hembeli (Conrad, 1838) (Unionacea: Margaritiferidae). Nautilus 102 (4): 159–163.

[TC89] Tapparone Canefri, T. 1889. Viaggio di Leonardo Fea in Birmania e regioni vicine. XVIII.—Molluschi terrestri e d’acqua dolce. Annali del Museo Civico di Storia Naturale di Genova, Serie 2a 7: 295–359.

[UM02] Upchurch, P., & J. Martin. 2002. The Rutland Cetiosaurus: the anatomy and relationships of a Middle Jurassic British sauropod dinosaur. Palaeontology 45 (6): 1049–1074.

[USDI77] USDI (United States Department of the Interior). 1977. Endangered and threatened wildlife and plants—republication of list of species. Federal Register 42: 36420–36431.

[V16] Vanatta, E. G. 1916. Rafinesque's types of Unio. Proceedings of the Academy of Natural Sciences of Philadelphia 67 (3): 549–559.

[WMP89] Way, C. M., A. C. Miller & B. S. Payne. 1989. The influence of physical factors on the distribution and abundance of freshwater mussels (Bivalvia: Unionidae) in the lower Tennessee River. Nautilus 103 (3): 96–98.

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