Trapezidens dolichorhynchus ( Tapparone-Canefri, 1889 )

Konopleva, Ekaterina S., Bolotov, Ivan N., Kondakov, Alexander V., Kononov, Oleg D., Gofarov, Mikhail Yu., Tomilova, Alena A., Lunn, Zau, Chan, Nyein, Win, Than & Vikhrev, Ilya V., 2020, A taxonomic review of Trapezidens (Bivalvia: Unionidae: Lamellidentini), a freshwater mussel genus endemic to Myanmar, with a description of a new species, Ecologica Montenegrina 27, pp. 45-57 : 52-53

Trapezidens dolichorhynchus ( Tapparone-Canefri, 1889)

Fig. 3b

= Unio marginalis var. obesa Hanley & Theobald (1876): 20 , Pl. 43, Fig. 3 . Type locality: River Iriwadi, Birmah. Primary homonym of Unio obesus Lea, 1831 . Type: Holotype BMNH_ 1907-12-30 -46 [by monotypy]; Natural History Museum, London, UK (examined by us).

= Unio dolichorhynchus Tapparone-Canefri (1889): 348 . Type locality: Mercato di Mandalay [Mandalay market]. Types: Whereabouts unknown, but probably in ZSI ( Prashad 1922).

= Unio scutum var. humilior Martens (1899): 45 , Pl. 5, Fig. 1 . Type locality: Irawaddi, bei Yenangyoung. Type: Holotype ZMB_49639; Museum für Naturkunde, Berlin, Germany (examined by us). Paratype: SMF 3625 (Chindwin bei Kalewa, O. Birmah. H. Rolle); Naturmuseum Senckenberg, Frankfurt, Germany (examined by us).

= Trapezidens obesa obesa ( Hanley & Theobald, 1876) . – Bolotov et al. (2017b): 10.

= Unio protensus Tapparone-Canefri (1889): 349 . Type locality: Prome, Bassa Birmania [Irrawaddy near Pyay city, approx. 18.8387°N, 95.2206°E]. Primary homonym of Unio protensus Lea, 1865 ; renamed Lamellidens canefrianus Simpson, 1900 . Types: Whereabouts unknown, but probably in ZSI ( Prashad 1922).

= Lamellidens canefrianus Simpson (1900): 857 . Type locality: Prome, Lower Burma [Irrawaddy near Pyay city, approx. 18.8387°N, 95.2206°E]. Replacement name for Unio protensus Tapparone-Canefri, 1889 .

= Unio protensus var. ellipticus Tapparone-Canefri (1889): 350 . Type locality: Prome, Bassa Birmania [Irrawaddy near Pyay city, approx. 18.8387°N, 95.2206°E]. Primary homonym of Unio elliptica Rafinesque, 1820 . Types: Whereabouts unknown, but probably in ZSI ( Prashad 1922).

= Unio gianellii Tapparone-Canefri (1889): 353 . Type locality: Mercato di Mandalay [Mandalay market]. Types: Whereabouts unknown, but probably in ZSI ( Prashad 1922).

Topotypes examined. MYANMAR: Ayeyarwady River near Tant Kyi village , 21.1567°N, 94.8050°E, 02.iii.2018, 16 specimens [ RMBH biv 417, including specimens RMBH biv 417_1, biv 417_2, and biv 417_3 being sequenced], Bolotov, Nyein Chan and Vikhrev leg.

Other material examined. MYANMAR: Myit Tha (Manipur) River, 23.22845°N, 94.1434°E, Ayeyarwady River basin, 02.ii.2018, 6 specimens [ RMBH biv 336, including specimens RMBH biv336_1, biv 336_2, and biv 336_3 being sequenced], Bolotov, Nyein Chan and Vikhrev leg ; Chindwin River, 23.1499°N, 94.3627°E, Ayeyarwady River basin, 04.ii.2018, 7 specimens [ RMBH biv 353 and biv 354, including specimens RMBH biv 353, biv 354_1, biv 354_2, and biv 354_3 being sequenced], Bolotov, Nyein Chan and Vikhrev leg.

Differential diagnosis. Shell large, very elongated, inequilateral, irregularly elliptic with slightly curved or straight ventral margin and slightly raised dorsal margin, rather thick and moderately inflated. Periostracum dark-brown with well visible growth lines. Pseudocardinal teeth massive, lateral teeth long and sharp, mussel scars deep.

Molecular diagnosis. Trapezidens dolichorhynchus is closely related to T. angustior and T. yeti sp. nov. (mean uncorrected COI p-distances: 2.14% and 1.96% respectively), but it can be distinguished from the sister species by two fixed substitutions in the COI gene fragment as follows: 479 T and 569 G; two fixed substitutions in 16S rRNA gene fragment as follows: 186 T and 196 C.

Distribution. Endemic to the Ayeyarwady River, Myanmar.

Comments. Phylogenetically and morphologically, specimens from the Ayeyarwady, Chindwin, and Manipur rivers do not have any significant differences. Our novel results support the morphology-based hypothesis that the nominal taxa Trapezidens dolichorhynchus (Ayeyarwady) and Unio scutum var. humilior (Chindwin and Manipur) are conspecific ( Bolotov et al. 2017b).

Figures

Figure 1. Distribution and the type localities of Trapezidens species in Myanmar. The numbers on the map indicate the type localities (green stars) and ranges (color filling) of certain species as follows: (1) Trapezidens yeti sp. nov.: Ye River basin. (2) T. scutum: Tanintharyi (Great Tenasserim) River basin. (3) T. angustior: Bago (Pegu), Sittaung, and Bilin river basins. (4) T. exolescens: Dawei (Tavoy) River basin. (5) T. dolichorhynchus: Ayeyarwady (Irrawaddy) River basin.

Figure 3. Shells of five Trapezidens species: a) T. angustior [topotype RMBH biv 382_3]; b) T. dolichorhynchus [topotype RMBH biv 417_2]; c) T. exolescens [topotype RMBH biv 145_12]; d) T. scutum [topotype RMBH biv 632_1]; e) T. yeti sp. nov. [holotype RMBH biv 616_1]. Scale bar = 20 mm. (Photos: Ekaterina S. Konopleva).