A new deep-sea species of Elliptiolucina Cosel & Bouchet, 2008 (Bivalvia, Lucinida, Lucinidae) from cold seep of the South China Sea

The increasing discoveries of new species of the family Lucinidae in the last two decades indicated a surprising diversity of chemosynthetic lucinids in the deep sea, especially in the Indo-West Pacific. However, only a few records have been reported from the South China Sea. A new lucinid species Elliptiolucina subovalis sp. nov. is here reported from a deep-sea cold seep site of the South China Sea. The new species is distinct from its congeners by possessing a strong anterior lateral tooth on the right valve and anterior tapering, subrectangular-oval shells. Sequences of three genes (18S rRNA, 28S rRNA, and CytB) were used to analyze its relationships with other species in the subfamily Myrteinae and confirm its taxonomic placement. The result supports the monophyly of Myrteinae but also demonstrates the polyphyly of Elliptiolucina. The new species has a close relationship with E. williamsae and Rostrilucina garuda, but is not closely related to congener E. ingens. By comparing morphological characters, we suggest that E. ingens should not belong to the genus Elliptiolucina. The basal two of three deep-sea clades recognized in Myrteinae may indicate the deep-sea origin of this subfamily. Our results add to the known diversity of deep-sea lucinids and molecular information for poorly studied Myrteinae and highlight the necessity of further investigation on deep-sea lucinids of the South China Sea.