Abstract
Cephalopods such as Euprymna berryi play vital ecological roles and hold potential for aquaculture, yet their development in the South China Sea remains understudied. This study aimed to verify the species identity of E. berryi from Sanya, Hainan, using diagnostic morphology supported by molecular markers and to elucidate its embryonic development to inform marine science and aquaculture. Specimens collected from Hongsha coastal waters underwent morphological examination (mantle shape, arm formula, beak structure, ovarian anatomy) and molecular sequencing (COI, 12S rRNA, 18S rRNA), with phylogenetic trees constructed using maximum likelihood in MEGA 11. Embryonic development was observed at 27–28 °C, with hatching rates and environmental effects analyzed via ANOVA and generalized additive models in R. Diagnostic morphology, together with COI and 12S rRNA placement, supported the assignment of the specimens to E. berryi, with bootstrap support values of 100% and 88%, respectively. Hatching began on Day 20, and the monitored egg set reached a final cumulative hatching rate of 97.26% by Day 27. Capsule removal was associated with earlier hatching endpoints, and many hatchlings retained yolk sacs. High mortality occurred during qualitative feeding observations with Artemia nauplii; diet quality was not tested. This study provides a documented developmental baseline for E. berryi in the South China Sea and demonstrates that incubation conditions critically influence embryogenesis and hatching success. The identified nutritional bottleneck highlights the need for optimized first-feed protocols to improve juvenile survival and advance captive rearing efforts for this promising aquaculture species.