Unio sumatrensis Dunker, 1852
Dunker, 1852. Zeitschr. f. Malakozool. 9: 52.
Type(s): TYPE ZMB_108722, Danau Luar, Sumatra.

Rectidens sumatrensis — Simpson (1900), Simpson (1914), Haas (1914), van Benthem Jutting (1953), Graf & Cummings (2007), ... Chen et al. (2025), Klymus et al. (2025), Campbell & Lydeard (2026), Wu et al. (2026), Zieritz et al. (2026)
Rectidens sumatrensis sumatrensis — Haas (1969)

Unio perakensis Morgan, 1885
Morgan, 1885. Bull. Soc. Zool. France 10: 424, pl. 9, figs. 3-4.

Rectidens perakensis — Simpson (1900), Simpson (1914), Haas (1914)
Rectidens sumatrensis perakensis — Haas (1969)
Rectidens sumatrensis — Pfeiffer et al. (2021)

Unio lingulatus Drouët & Chaper, 1892
Drouët & Chaper, 1892. Mém. Soc. Zool. France 5: 149, pl. 5, figs. 7-9.
Drouët, 1893. J. de Conch. 41: 42.
Type(s): SYNTYPE MNHN_IM-2000-1737, Borneo.

Rectidens lingulatus — Simpson (1900), Simpson (1914), Haas (1914), Graf & Cummings (2007), Bogan (2010), Zieritz et al. (2018), Graf & Cummings (2021), Sahidin et al. (2021)
Rectidens lingulatus lingulatus — Haas (1969)
Rectidens sumatrensis — Pfeiffer et al. (2021)

Unio prolongatus Drouët, 1894
Drouët, 1894. Rev. Biol. Nord France 6: 216, text fig. 1.
Drouët, 1895. J. de Conch. 43: 36, sp. 111.
(homonym of Unio calamitarum var. B prolongata Fischer & Crosse, 1894)

Rectidens prolongatus — Simpson (1900), Simpson (1914), Haas (1914), Thiele (1934), Haas (1969)
Rectidens lingulatus prolongatus — Haas (1969)
Rectidens lingulatus — Graf & Cummings (2007), Graf & Cummings (2021)
Rectidens sumatrensis — Pfeiffer et al. (2021)

Microcondylaea gracilis Strubell, 1897
Strubell, 1897. Nachr. Bl. Dtsch. Malak. Ges. 29: 8.
Type(s): TYPE SMF_3610, S. Sumatra.

Rectidens gracilis — Simpson (1914), Haas (1914), Marwoto (1987)
Rectidens sumatrensis gracilis — Haas (1969)
Rectidens sumatrensis — Pfeiffer et al. (2021)

Unio palembangensis Strubell, 1897
Strubell, 1897. Nachr. Bl. Dtsch. Malak. Ges. 29: 10.
Type(s): TYPE SMF_3611, S. Sumatra.

— Simpson (1900)
Unio palembangensis — Martens (1900)
Rectidens palembangensis — Simpson (1914)
Rectidens gracilis — Haas (1914)
Rectidens sumatrensis gracilis — Haas (1969)
Rectidens sumatrensis — Pfeiffer et al. (2021)

Unio pahangensis E.A. Smith, 1899
E.A. Smith, 1899. Proc. Malac. Soc. London 3: 315, text fig.
Type(s): HOLOTYPE (MONOTYPY) BMNH_99-9-4-1, Pahang River, Malay Pennisula.

Rectidens pahangensis — Simpson (1900), Simpson (1914)
Rectidens perakensis — Haas (1914)
— Haas (1969)
Rectidens sumatrensis — Pfeiffer et al. (2021)

Unio pressirostris Martens, 1900
Martens, 1900. Nachr. Bl. Dtsch. Malak. Ges. 32: 14.
Type(s): TYPE ZMB_51794, Indragiri Fluss, Sumatra.

Unio pressirostris — Martens (1900)
Rectidens pressirostris — Simpson (1914), Haas (1914)
Rectidens sumatrensis pressirostris — Haas (1969)
Rectidens sumatrensis — Pfeiffer et al. (2021)

Unio palembangensis var. pahumbaensis Martens, 1900
Martens, 1900. Nachr. Bl. Dtsch. Malak. Ges. 32: 14 [as ‘pahumbaënsis’].
(intro'd as intra-sp. of Unio palembangensis Strubell, 1897)

Unio palembangensis var. pahumbaënsis — Martens (1900)
Rectidens palembangensis var. pahumbaënsis — Simpson (1914)
Rectidens gracilis — Haas (1914)
Rectidens sumatrensis gracilis — Haas (1969)
Rectidens sumatrensis — Pfeiffer et al. (2021)

Unio perakensis Preston, 1912
Preston, 1912. Rec. Ind. Mus. 7: 287, pl. 8, figs. 5-6.
(renamed Rectidens prestoni Simpson, 1914; homonym of Unio perakensis Morgan, 1885)

Unio perakensis — Preston (1912)
Rectidens prestoni — Simpson (1914)
Rectidens perakensis — Haas (1914)
Rectidens sumatrensis — Pfeiffer et al. (2021)

Rectidens prestoni Simpson, 1914
Simpson, 1914. Descr. Cat. Naiades: 1159.
(new name for Unio perakensis Preston, 1912)

Rectidens prestoni — Simpson (1914)
— Haas (1969)
Rectidens sumatrensis — Pfeiffer et al. (2021)

Unio pahoembaensis Haas, 1912
‘Martens’ Haas, 1912. Conch. Cab. 9 (pt. 2, h. 46): pl. 28, figs. 1-2.
(error for Unio palembangensis var. pahumbaensis Martens, 1900)

Rectidens palembangensis var. pahumbaënsis — Simpson (1914)