A single origin for the limnetic-euryhaline taxa in the Corbulidae (Bivalvia)
The bivalve family Corbulidae, known colloquially as 'basket clams', includes species tolerating a wide variety of habitats ranging from open marine to freshwater. Previous studies of corbulid phylogenetics have been based mainly on shell morphology and to some extent soft tissue anatomy. However, these studies have been inadequate for corbulid classification because of difficulties in determining the inter-relationships of primarily marine species with non-marine species, the latter commonly exhibiting highly divergent morphological, ecological and environmental characteristics from their marine counterparts. The first molecular phylogenetic study of the Corbulidae is presented herein, analysing DNA sequences from the 18S rRNA and 28S rRNA genes, separately and in combination. Fifteen corbulid species and 14 outgroup taxa were included in the analyses. Corbulidae is resolved as monophyletic, comprising three groups with varying support. The non-marine species form one group that we name as the subclade 'limnetic-euryhaline Corbulidae' (LEC) and comprising the genera Lentidium, Erodona and Potamocorbula. This LEC, which is consistently recovered as monophyletic, is globally distributed. The marine Corbulidae are divided into two well-supported lineages in combined analyses although there are inconsistencies in their membership between single-gene analyses. One of the two lineages consists of primarily Western Pacific taxa and the other of North American and Caribbean taxa. Finally, the authors advocate further study on the LEC to mitigate potential biological invasions beyond their native distribution.