A new genus and two new species of freshwater mussels (Unionidae) from western Indochina

Ekaterina S Konopleva,Olga V Aksenova,Ilya V Vikhrev,Alexander V Kondakov,Zau Lunn,Nyein Chan,John M Pfeiffer,Ivan N Bolotov,Mikhail Yu Gofarov

doi:10.1038/s41598-019-39365-1

Abstract

The systematics of Oriental freshwater mussels (Bivalvia: Unionidae) is poorly known. Here, we present an integrative revision of the genus Trapezoideus Simpson, 1900 to further understanding of freshwater mussel diversity in the region. We demonstrate that Trapezoideus as currently circumscribed is non-monophyletic, with its former species belonging to six other genera, one of which is new to science and described here. We recognize Trapezoideus as a monotypic genus, comprised of the type species, T. foliaceus. Trapezoideus comptus, T. misellus, T. pallegoixi, and T. peninsularis are transferred to the genus Contradens, T. subclathratus is moved to Indonaia, and T. theca is transferred to Lamellidens. Trapezoideus prashadi is found to be a junior synonym of Arcidopsis footei. Trapezoideus dallianus, T. nesemanni, T. panhai, T. peguensis, and two species new to science are placed in Yaukthwagen. nov. This genus appears to be endemic of the Western Indochina Subregion. The two new species, Yaukthwa paiensissp. nov. and Y. inlenensissp. nov., are both endemic to the Salween River basin. Our results highlight that Southeast Asia is a species-rich freshwater mussel diversity hotspot with numerous local endemic species, which are in need of special conservation efforts.

Highlights

Freshwater mussels (Unionoida) are a diverse and globally distributed clade[1,2]
Our multi-locus phylogeny based on the mitochondrial cytochrome c oxidase subunit I (COI), small ribosomal RNA (16 S rRNA), and the nuclear large ribosomal RNA (28 S rRNA) gene fragments clearly indicates that the genus Trapezoideus sensu Bolotov et al 2017 in its current understanding is a polyphyletic entity (Fig. 1; Supplementary Table 1)
We suggest that Trapezoideus peninsularis is a member of the genus Contradens, T. theca belongs to Lamellidens, and Trapezoideus prashadi is a junior synonym of Arcidopsis footei

Summary

Introduction

Freshwater mussels (Unionoida) are a diverse and globally distributed clade[1,2]. There are two major freshwater mussel biodiversity hotspots, i.e. the Southeastern USA and East, South and Southeast Asia[3,4]. Several recent phylogenetic studies have substantially revised the taxonomy, morphological evolution, and historical biogeography of Asian freshwater mussels[4,5,6,7,8,9,10,11,12,13] but many taxa remain poorly characterized. The genus Trapezoideus Simpson, 1900 has been included in several recent phylogenetic studies[5,8,12,13,14] but taxon sampling within the genus remains largely incomplete, and no published study has yet to include the type species Unio foliaceus Gould, 184314. Recent collections of putative Unio foliaceus and several other species previously assigned to Trapezoideus (Trapezoideus comptus, T. misellus, T. pallegoixi, and T. subclathratus), as well as several morphologically similar specimens collected from the poorly characterized Salween River provide the basis for a more robust revision of the genus Trapezoideus and the tribe Contradentini more generally

Methods

Results

Conclusion