Embryonic development of the paintpot cuttlefish ( Ascarosepion tullbergi ), with emphasis on benthic traits during organogenesis

Abstract The paintpot cuttlefish Ascarosepion tullbergi (Appellöf, 1886) exhibits a distinctly benthic lifestyle, in contrast to the typical ontogenetic shift from benthic to nekto-benthic modes observed in most cuttlefish species. While many cuttlefish initially attach to substrates using arms IV and the ventral mantle, they generally transition to swimming-based locomotion as they mature. A. tullbergi , however, remains benthic throughout its life, relying on arms IV and the lateral edges of the ventral mantle for attachment and using an ambling gait for locomotion from hatching to adulthood. Despite the ecological significance of benthic specialisation, embryonic development in fully benthic cuttlefish remains poorly studied, as previous research has primarily focused on nekto-benthic species. To address this gap, we described the embryonic development of A. tullbergi and compared it with that of other sepiid species. Although the overall developmental pattern of A. tullbergi is broadly similar to that of other nekto-benthic cuttlefish, this species exhibits a pronounced early investment in benthic traits, particularly in the development of arms IV and the lateral edges of the mantle. Specifically, arms IV in A. tullbergi develop earlier and more prominently than in other Sepiidae species that undergo ontogenetic shifts in life mode. This early specialisation underscores the unique ecological strategy of A. tullbergi and reflects its adaptation to a lifelong benthic niche. The present study provides a description of embryonic development in A. tullbergi and contributes to a deeper understanding of cephalopod diversity.