Worldwide 12 species of Leydigia are accepted as valid, see Kotov (2009) for a key to the genus.
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References
(1) KOTOV, A.A. 2009. A revision of Leydigia Kurz, 1875 (Anomopoda, Cladocera, Branchiopoda), and subgeneric differentiation within the genus. Zootaxa. 2082: 1-84.