Contradens contradens (Lea, 1838) Fig. 3C

Unio contradens Lea, 1838: 75, pl. 18, fig. 58. Type locality: Java.

Uniandra contradens tumidula: Brandt 1974: 290-291, pl. 24, figs 51, 52.

Uniandra contradens rustica: Brandt 1974: 291-292, pl. 24, fig. 53.

Uniandra contradens fischeriana: Brandt 1974: 292, pl. 24, fig. 55.

Material examined.

CIFI.MOL.017, CIFI.MOL.018, MUMNH.UNI.2621, MUMNH.UNI.2629, MUMNH.UNI.2633, MUMNH.UNI.2648, MUMNH.UNI.2651, ZRC.MOL.015639.

Distribution and habitat.

Tonle Sap Lake at Kampong Chhnang and Siem Reap Provinces, and Chhnok Tru landing point (locality no. 8, 11, 18, 36, 37, and 39); in soft muddy substrate.

Remarks.

Not sold for food, collected as by-catch of Corbicula and Mekongia harvests, and were often observed to be discarded along with other large unionids. Contradens contradens was recently noted for its high varation in shell morphology dued to phenotypic plasticity (Jeratthitikul et al. 2019b). The species recognised here may represent one of Contradens contradens varations or could be recognised as a distinct species, e.g., Unio dautzenbergi Morlet, 1889. Further molecular studies are necessary to confirm the taxonomic status. The present collected specimens are strongly sculptured with irregularly concentric wrinkles throughout the shell, similar to some populations from Chao Praya basin, Thailand.