First report of monovitellinic twin embryos of Bignose fanskate, Symterygia acuta Garman 1877 (Rajiformes, Arhynchobatidae)

This study reports the first case of monovitellinic twins in Sympterygia acuta , found in its natural habitat. While embryonic development in this species typically results in a single embryo per egg capsule, two embryos were found sharing a single yolk sac . The egg capsule and embryos exhibited morphological characteristics within the normal range for the species, though differences in the size and thickness of the yolk stalk were noted. This case is compared to other reports of monozygotic twins in fish and elasmobranchs, but the exact causes remain unknown. Potential environmental or evolutionary influences are discussed.