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