Caputi L, Andreakis N, Mastrototaro F, Cirino P, Vassillo M, Sordino P.

Proc Natl Acad Sci U S A. 2007 May 29;104(22):9364-9 doi:10.1073/pnas.0610158104

Cryptic speciation in a model invertebrate chordate.

Only C. robusta female gametes could be fertilised by sperm from either C. rob or C. int. Hybrids were infertile. Allospecific crosses between two sympatric strains from Plymouth could not develop beyond a few cell cleavages.