Short Communication |
Corresponding author: Ivan N. Bolotov ( inepras@yandex.ru ) Academic editor: Yasen Mutafchiev
© 2019 Ivan N. Bolotov, Ilya V. Vikhrev, Manuel Lopes-Lima, Mikhail Y. Gofarov, Ekaterina S. Konopleva, Zau Lunn, Nyein Chan, Arthur E. Bogan.
This is an open access article distributed under the terms of the CC0 Public Domain Dedication.
Citation:
Bolotov IN, Vikhrev IV, Lopes-Lima M, Gofarov MY, Konopleva ES, Lunn Z, Chan N, Bogan AE (2019) Indonaia rectangularis (Tapparone-Canefri, 1889), comb. nov., a forgotten freshwater mussel species from Myanmar (Bivalvia, Unionidae). ZooKeys 852: 23-30. https://doi.org/10.3897/zookeys.852.33898
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Unio rectangularis Tapparone-Canefri, 1889 is a little-known nominal species of freshwater mussels described from a tributary of the Ayeyarwady River in Myanmar. This taxon was considered a synonym of Gibbosula laosensis (Lea, 1863), a margaritiferid species. However, the range of Gibbosula laosensis does not encompass the Ayeyarwady River watershed. Here we re-examine the holotype of Unio rectangularis and provide a conchological re-description of this species. Based on conchological features such as the shell shape, elevated umbo, and the structure of lateral and pseudocardinal teeth, we transfer this taxon to the genus Indonaia Prashad, 1918 and propose I. rectangularis (Tapparone-Canefri, 1889), comb. nov. It appears to be a rare freshwater mussel species with a restricted range, because it has not been found since the original description. Two additional species in this genus are known from Myanmar, i.e. Indonaia andersoniana (Nevill, 1877) and I. subclathrata (Martens, 1899).
Ayeyarwady River, Indochinellini, Margaritiferidae, Parreysiinae, Southeast Asia, Unionidae
Gibbosula laosensis (Lea, 1863) (Bivalvia, Margaritiferidae) is an endangered freshwater mussel species from Southeast Asia (
Leonardo Fea, an adventurous Italian pioneer and explorer, found a single shell of Unio rectangularis among large collections of non-marine molluscs from British Burma during his travels in 1885–1887 (
Later,
We revise the generic placement of Unio rectangularis and discuss its prospective taxonomic status based on morphological study of the type specimen.
We studied the holotype of Unio rectangularis in the Museo Civico di Storia Naturale di Genovay (
=Unio rectangularis
=Margaritanopsis rectangularis (Tapparone-Canefri, 1889). –
Holotype in
Holotype of Indonaia rectangularis (Tapparone-Canefri, 1889), comb. nov. [
Teinzo (presently Teinthaw village), 24.3978N, 97.2519E, Moolay River (Mole Chaung in Burmese), hills E of Bhamo (L. Fea), alt. 110 m a.s.l., Ayeyarwady Basin, Myanmar (
As
Specimens of Indonaia andersoniana (Nevill, 1877) and I. subclathrata (Martens, 1899) from Myanmar [RMBH biv450_2 and RMBH biv347_2, respectively]. A, B Shell of I. andersoniana, lateral view: inner side of the left valve and outer side of the right valve (A); vice versa (B) C shell of I. andersoniana, dorsal view D, E shell of I. subclathrata, lateral view: inner side of the left valve and outer side of the right valve (D); vice versa (E) F shell of I. subclathrata, dorsal view. Scale bar: 5 mm. (Photos: Ekaterina S. Konopleva).
Shell length 34.2 mm, height 20.4 mm, width 16.2 mm. Shell thick, obovate, inequilateral, with broader posterior side. Dorsal margin slightly convex. Ventral margin nearly straight. Anterior margin rounded. Posterior margin slightly elevated posteriorly, with an inconspicuous wing. Umbo prominent, elevated, rounded, slightly eroded. Shell surface mostly smooth. In the posterior-dorsal area, regular ridges cross the growth lines and form a clear rectangular pattern. In the anterior-dorsal area, curved, lamella-like ridges closely spaced along growth lines. Periostracum light olive-brown, with two parallel, slightly curved green bands along posterior-dorsal area; inner band with a broad greenish extension posteriorly. Nacre silver-white. Umbo cavity deep. Anterior adductor scar round, shallow but well marked. Posterior adductor scar oval, very shallow, unclear. Mantle attachment scars absent. Pseudocardinal teeth are thick, lamella-like, very elongated, two teeth in the right valve and one tooth in the left valve. Lateral teeth well developed, thick, elongated and straight, one tooth in the right valve and two teeth in the left valve. Soft body morphology and anatomy unknown.
Unio rectangularis was originally described based on a single specimen with a shell 34.2 mm long, 20 mm high and 16 mm wide (
This species is known only from the type locality, a tributary of the Ayeyarwady River (Fig.
The results of our study reveal that Unio rectangularis is not a margaritiferid because it does not have mantle attachment scars, the most prominent diagnostic feature of the Margaritiferidae (
Indonaia represents the most divergent phylogenetic clade among the tribe Indochinellini (
1 | Shell surface with radial ridges covering the entire shell disc |
I. subclathrata (Martens, 1899) |
– | Shell surface without radial ridges on the shell disc | 2 |
2 | Shell surface mostly smooth, while regular ridges cross the growth lines and form a clear rectangular pattern in the posterior-dorsal area, and curved, lamella-like ridges closely spaced along growth lines in the anterior-dorsal area |
I. rectangularis (Tapparone-Canefri, 1889), comb. nov. |
– | Shell surface smooth |
I. andersoniana (Nevill, 1877) |
This work was partly funded by grants from the Russian Ministry of Education and Science (Project No. 6.2343.2017/4.6), Federal Agency for Scientific Organizations (Project No. AAAA-A18-118012390161-9), National Geographic Society (Project No. NGS-274R-18), Russian Foundation for Basic Research (Project Nos. 16-34-00638 and 18-34-20033), and Northern Arctic Federal University. Fundação para a Ciência e a Tecnologia – FCT supported MLL under grant No. SFRH/BD/115728/2016. We thank Maria Tavano, curator of the invertebrate collection of