The majority of morphological abnormalities reported for elasmobranchs are cases of bicephalia.This contribution describes the third confirmed case worldwide and the first in the South Atlantic of diprosopus tetrophthalmus (craniofacial duplication) in a foetus of blue shark, Prionace glauca (Linnaeus, 1758), from a female caught off Shower Caps the Brazilian coast (26°36′11′′S, 45°56′00′′W) in July 2007.The specimen is described and compared to normal specimens from the same size and to another one with similar deformities from Chile.
The embryo is smaller than a normal embryo, with deformities in the skull, head muscles and curvature of Calls the vertebral column.