Molecular data confirm synonymy of Roscovite molgulid ascidians

We used molecular data to compare Molgula echinosiphonica Lacaze-Duthiers, 1877 from Roscoff, France and Molgula citrina Alder & Hancock, 1848 from the eastern coast of the United States and northern French Atlantic coast in order to confirm that these described molgulids are two populations of the same species, Molgula citrina. First, we compared sequences of two nuclear genes, 18S rDNA and 28S rDNA, from these species and found that they were 100% identical, indicating a single species. Then we reviewed the available literature describing their differences and compared them to our recent observations and suggest that the described differences may be due to developmental plasticity in the species. Molgula citrina (1848) has precedence over M. echinosiphonica (1877), so we retained M. citrina for this species. We encourage professional taxonomists to consider collaborations using molecular markers to solve cases of synonymy in the literature caused by phenotypic plasticity and/or doubtful morphological descriptions.