1. Species Posidonia lata Betekhtina, 1979 † (accepted > unreplaced junior homonym, junior homonym of Posidonia lata Studer, 1838)
2. Subgenus Posidonia (Karadjalia) Sadykov, 1962 † accepted as Guerichia Rzehak, 1910 † (unaccepted > junior objective synonym, same type species)
   1. Species Posidonia (Karadjalia) bairensis Sadykov, 1962 † accepted as Guerichia bairensis (Sadykov, 1962) † (unaccepted > superseded combination)
   2. Species Posidonia (Karadjalia) kazakhstanensis Sadykov, 1962 † accepted as Guerichia kazakhstanensis (Sadykov, 1962) † (unaccepted > superseded combination)
   3. Species Posidonia (Karadjalia) mariannae (B. I. Chernyshev, 1941) † accepted as Guerichia mariannae (B. I. Chernyshev, 1941) † (unaccepted > superseded combination)
   4. Species Posidonia (Karadjalia) nalivkini Sadykov, 1962 † accepted as Guerichia nalivkini (Sadykov, 1962) † (unaccepted > superseded combination)
   5. Species Posidonia (Karadjalia) ovata Sadykov, 1962 † accepted as Guerichia ovata (Sadykov, 1962) † (unaccepted > superseded combination)
   6. Species Posidonia (Karadjalia) simorini Sadykov, 1962 † accepted as Guerichia simorini (Sadykov, 1962) † (unaccepted > superseded combination)
   7. Species Posidonia (Karadjalia) venusta (Münster, 1840) † accepted as Guerichia venusta (Münster, 1840) † (unaccepted > superseded combination)
   8. Species Posidonia (Karadjalia) venustiformis Sadykov, 1962 † accepted as Guerichia venustiformis (Sadykov, 1962) † (unaccepted > superseded combination)
3. Species Posidonia alveata Conrad, 1841 † accepted as Grammysioidea alveata (Conrad, 1841) † (unaccepted > superseded combination)
4. Species Posidonia arcuata Conrad, 1841 † accepted as Grammysioidea arcuata (Conrad, 1841) † (unaccepted > superseded combination)
5. Species Posidonia buchii Roemer, 1836 † accepted as Bositra buchii (Roemer, 1836) † (unaccepted > superseded combination, original combination)
6. Species Posidonia hians (Waldschmidt, 1885) † accepted as Pterochaenia insidiosa (Barrande, 1881) † (unaccepted > junior subjective synonym)
7. Species Posidonia lirata Conrad, 1838 † accepted as Paracyclas lirata (Conrad, 1838) † (unaccepted > superseded combination)
8. Species Posidonia marcellensis J. M. Clarke, 1904 † accepted as Pterochaenia marcellensis (J. M. Clarke, 1904) † (unaccepted > superseded combination)
9. Species Posidonia mariannae B. I. Chernyshev, 1941 † accepted as Guerichia mariannae (B. I. Chernyshev, 1941) † (unaccepted > superseded combination)
10. Species Posidonia mimer Öberg, 1877 † accepted as Peribositria mimer (Öberg, 1877) † (unaccepted > superseded combination)
11. Species Posidonia minuta Zieten, 1833 † accepted as Euestheria minuta (Zieten, 1833) † (unaccepted > superseded combination, not a mollusk)
12. Species Posidonia ornati Quenstedt, 1851 † accepted as Bositra ornati (Quenstedt, 1851) † (unaccepted > superseded combination)
13. Species Posidonia pannonica (Mojsisovics, 1873) † accepted as Peribositria pannonica (Mojsisovics, 1873) † (unaccepted > superseded combination)
14. Species Posidonia somaliensis L. R. Cox, 1935 † accepted as Bositra buchii (Roemer, 1836) † (unaccepted > junior subjective synonym)
15. Subgenus Posidonia (Posidonia) Bronn, 1828 † represented as Posidonia Bronn, 1828 †
    1. Species Posidonia (Posidonia) kavuni Sadykov, 1962 † (uncertain > unassessed)
    2. Species Posidonia (Posidonia) orbicularis Sadykov, 1962 † (uncertain > unassessed, junior homonym of Posidonia orbicularis Münster, 1835)
    3. Species Posidonia (Posidonia) protobecheri Sadykov, 1962 † (uncertain > unassessed)
    4. Species Posidonia (Posidonia) striata Sadykov, 1962 † (uncertain > unassessed)
16. Species Posidonia aequilatera Vukhuc, 1965 † (uncertain > unassessed)
17. Species Posidonia anomala Münster, 1835 † (uncertain > unassessed)
18. Species Posidonia becheri Bronn, 1828 † (uncertain > unassessed)
19. Species Posidonia bronnii Zieten, 1833 † (uncertain > unassessed)
20. Species Posidonia canaliculata Goldfuss, 1835 † (uncertain > unassessed)
21. Species Posidonia gigantea Münster, 1835 † (uncertain > unassessed)
22. Species Posidonia orbicularis Münster, 1835 † (uncertain > unassessed)
23. Species Posidonia qijiagouensis Z.-R. Yang, 1983 † (uncertain > unassessed)
24. Species Posidonia radiata Goldfuss, 1835 † (uncertain > unassessed)
25. Species Posidonia socialis Münster, 1835 † (uncertain > unassessed)
26. Species Posidonia tamugangensis Z.-R. Yang, 1983 † (uncertain > unassessed)

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