The idea of a single-eyed “cyclops shark” often appears in sensationalized online stories. Specimens exhibiting this feature have been recovered, confirming the phenomenon is real. However, this animal is not a newly discovered species, but rather a rare case of a severe congenital disorder. The characteristic single eye results from a developmental anomaly that occurs during the earliest stages of fetal growth. Understanding this rare occurrence requires looking into the underlying biological mechanisms of birth defects in marine life.
The Anatomy of the Discovery
The most well-known example occurred in 2011 off the coast of Mexico. A fisherman, Enrique Lucero León, caught a pregnant dusky shark (Carcharhinus obscurus) near Cerralvo Island. He discovered a single, pale male fetus among the ten pups in the womb that possessed a striking deformity.
This particular fetus was approximately 22 inches long and featured a single, large eye socket positioned centrally on the head. The specimen also lacked a proper snout, with the area above the single eye being deformed. The fisherman shared images of the shocking finding, which quickly went viral and were initially dismissed as a hoax.
Biologists from the Interdisciplinary Center of Marine Sciences in La Paz, Mexico, eventually examined the specimen. They confirmed the authenticity of the fetus and diagnosed the condition as cyclopia. This is an extremely rare congenital defect documented in various animal species, though rarely found in such a developed state.
The Developmental Biology of Cyclopia
The condition is cyclopia, the most extreme form of a broader disorder called holoprosencephaly (HPE). This disorder originates when the developing forebrain, or prosencephalon, fails to properly cleave into two distinct cerebral hemispheres during the embryonic stage. This failure to divide the brain mass also prevents the subsequent separation of the facial structures.
Normally, the forebrain’s segmentation dictates the formation of two separate eye fields, which develop into two distinct orbits and eyes. In cases of HPE, the lack of proper midline development means the orbits remain fused or merge into a single cavity. This profound brain malformation is directly responsible for the characteristic single eye and the associated absence of a nose or the formation of a tube-like appendage above the eye.
The underlying causes of HPE in sharks are not fully understood, but research suggests several factors can disrupt this delicate process. Genetic mutations or chromosomal abnormalities can play a role in the failed segmentation of the neural tube. Environmental factors are also considered, such as exposure to toxins, nutritional deficiencies, or severe infections during gestation.
Survival and Rarity in the Wild
The shocking appearance of a cyclops shark naturally raises the question of whether such an animal could survive in the ocean. Based on scientific observation, these individuals are virtually non-viable. The severe neurological and structural defects that cause the single eye are often accompanied by other debilitating internal malformations.
In the dusky shark fetus, the lack of proper head development meant the absence of functional olfactory organs, making it unable to detect prey or navigate. The associated brain defects and malformations in other organ systems, such as the respiratory tract, make survival nearly impossible. Many fetuses with cyclopia are stillborn or miscarried before reaching full term.
The few documented cases of cyclops sharks have all been found as fetuses within pregnant females. This lack of viability explains why the creature is so rare and why no free-swimming adult cyclops shark has ever been observed. The phenomenon is a spontaneous developmental accident, not a stable genetic trait that could create a new population.