First Record of Triplet Embryos in Sea Turtles: Evidence of Natural Polyembryony in a Wild Green Turtle (Chelonia mydas) Nest From Guanahacabibes, Cuba.

Polyembryony is an exceptionally rare developmental phenomenon in reptiles and is typically documented as isolated cases of monozygotic twinning. Evidence of triplet embryos in chelonians is particularly scarce and has previously been reported only in managed or captive conditions. We report and describe an exceptional case of polyembryonic triplet embryos from a wild green turtle (Chelonia mydas) nest on the Guanahacabibes Peninsula, Cuba-representing one of only two confirmed chelonian triplet records and the first documented under natural incubation conditions in a sea turtle nest. The nest achieved 91.6% hatching success and normal hatchling performance; three of the 11 unhatched eggs (27.3%) contained embryos with congenital malformations, including a polyembryonic triplet embryo configuration. Morphological assessment, developmental staging, and yolk sac examination demonstrated three embryos attached to a single continuous yolk mass, each possessing an independent vitelline vascular network, consistent with a monozygotic origin. Marked developmental asymmetry and craniofacial malformations in one embryo are compatible with resource limitation and asymmetric sibling competition within a shared yolk environment. Histological analysis of urogenital tissues revealed ovarian-type gonads in all three embryos, consistent with the expected female-biased sex ratios at higher incubation temperatures. These findings provide robust evidence of polyembryony under natural incubation conditions and highlight the developmental constraints inherent to multi-embryo development in sea turtles, underscoring the importance of long-term nest monitoring for detecting rare embryological events.