| Popis: |
Planktonic octopuses undergo a transitional period from a pelagic lifestyle to the predominantly benthic life of the juvenile stage, known as settlement, that is scarcely documented in the wild or captivity. In this work two generations of the common octopus, Octopus vulgaris, were reared in captivity and three different stages were defined for the settlement phase based on morphological, anatomical, and behavioural changes: pre-settlement or “tactile” stage, settlement, and post-settlement or “ninja” stage. Before settlement the swimming planktonic paralarvae are transparent with 65–80 chromatophores, iridophores covering eyes and digestive system, Kölliker organs, circular pupils, ~ 20 suckers, and mantle length (ML) bigger than total length (TL; ML/TL > 60%). The “tactile” stage (ML/TL from 65 − 55% and ~ 20–25 suckers) is marked by the onset of pre-settlement reflexes, where the late paralarvae touch the walls and bottom of the tank and start crawling clumsily. Morphologically, the paralarvae are transparent with increasing chromatophores and iridophores along the arms and the dorsal area of head and mantle. During the settlement stage (~ 55 − 48% ML/TL, and ~ 25–35 suckers), there is an exponential increase of chromatophores in the dorsal area and a marked change in behaviour, with paralarvae showing strong negative phototaxis, looking for shelter when disturbed. The skin is still transparent but new chromatic cells (leucophores) start to develop and the Kölliker organs are almost lost. During the post-settlement stage (~ 48 − 40% ML/TL, > 35 suckers) the chromatic cells keep increasing exponentially, giving a pale look to the skin. The early juveniles have horizontal pupils, with the “eye-bar” and display very fast and coordinated movements like “ninjas”. The start of the benthic phase is marked by the presence of skin sculptural components (papillae and cirrha) and the display of complex chromatic and body patterns. |
