Information on morphological abnormalities in the cephalic region of three female blue sharks' (Prionace glauca) foetuses found in Baja California Sur, Mexico, is included. In one foetus with bicephaly, the liver was shared. In the other two foetuses they do not have eyes, and part of their snout was not well-developed, with malformations in cranial cartilage and gill slits. A possible explanation for these deformities in blue shark embryos is that the blue shark is the most fecund shark worldwide with the highest number of embryos produced and not all embryos can be developed in their small uteri.
