Global genetic homogeneity in the deep-sea foraminiferan Epistominella exigua (Rotaliida: Pseudoparrellidae)*

Epistominella exigua is one of the most common deep-sea foraminiferal morphospecies and has a world-wide distribution. A recent molecular study revealed high genetic similarity between Arctic, Atlantic and Antarctic populations of this species. Here, we show that the small-subunit (SSU) and internal transcribed spacer (ITS) rDNA sequences of an E. exigua population from Pacific are almost identical to those reported previously from the other three oceans. This result confirms the genetic homogeneity of E. exigua, which contrasts with the prevalence of highly differentiated populations in planktonic and shallow-water benthic foraminiferans. We discuss special features of diversifications mechanisms in the deep sea that may be responsible for the lack of genetic differentiation and global distribution of some meiofauna species.