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Table 1 Hallmarks of each developmental stage in O. vulgaris

From: A practical staging atlas to study embryonic development of Octopus vulgaris under controlled laboratory conditions

Stage 0Cleavage
Stage IMorula (advanced cleavage)
Stage IIBlastula; disk flatter
Stage IIIOnset of epiboly
Stage IVFormation of the germinal disk, as wide as the yolk
Stage VEpiboly reaches 1/4th of the yolk
Stage VIEpiboly reaches 1/2nd of the yolk
Stage VII.1Epiboly reaches 3/4th of the yolk
Visible thickening of placodes starts
Stage VII.2Embryo completed first reversion
Primordia of eyes, mouth, mantle and arms clearly visible
Stage VIIIMouth and eye invagination
Mantle elevated and embryo thicker
Funnel pouches visible in lateral view
Stage IXFirst eye pigmentation (yellowish)
Primordia more prominent
Funnel tube rudiments are distinct
Contraction of yolk envelope evident
Stage XMantle flat, no depression in the middle
Eye vesicles sticking out with light orange retina (“saddle” shape)
Funnel tube rudiments fuse at the ventral margins
Stage XIMantle tilted
Funnel tube rudiments bended towards midline
Arm buds ‘elevated’ from yolk
Stage XII.1Mantle thicker and covers 1/2nd of gills
Funnel tube rudiments start to form a tube ventrally
First suckers recognizable on the posterior side
Stage XII.2Mantle bowl-shaped
Funnel formed siphon at ventral extremity
Stage XIIIMantle is bigger
Formation of the funnel complete
Arms elongated and pointed with (3) prominent suckers
Stage XIVMantle as wide as long and cube-shaped, covers gills completely
Heartbeat starts
Embryo and yolk have equal size
Stage XV.1Mantle completely covers ventral margin of funnel
Inner yolk strongly constricted (connection inner and outer yolk sac very thin)
Appearance of two chromatophores laterally from the funnel
Stage XV.2Mouth encircled by anterior arms
First chromatophores on posterior mantle appear
Stage XVIMouth completely covered by arm crown
Yolk size 1/3rd of embryo + yolk
Few chromatophores on anterior mantle evident
Stage XVIIChromatophores darker and more numerous
Stage XVIII.1Yolk size 1/4th of embryo + yolk
Posterior chromatophores darker and chromatophores appear next to the eye
Embryo more active in egg (mantle contraction)
Stage XVIII.2Anterior chromatophores darker. Chromatophores react to light stimulus
Stage XIX.1Eyes tilted and covered with iridophores
Yolk size 1/6th of embryo + yolk
Embryos react to mechanical stimulus
Pigmentation of ink sac
Stage XIX.2Embryos completed second reversion
Stage XX.1Minimal outer yolk sack
Chromatophore expansion and contraction more widely distributed
Stage XX.2Absence of outer yolk