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Fertilized egg
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Stage 1
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Stage 1
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Newly laid fertilized egg that did not finish maturation
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Segmentation (cleavage)
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First maturation division
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Stage 2
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Stage 1
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First polar body
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Segmentation (cleavage)
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Second maturation division
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Stage 3
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Stage 1
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3 polar bodies
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Segmentation (cleavage)
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2 cells, first cleavage
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Stage 4
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Stage 2
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Two partially separated cells
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Segmentation (cleavage)
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4 cells, second cleavage
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Stage 5
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Stage 3
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Four partially separated cells
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Segmentation (cleavage)
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8 cells, third cleavage
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Stage 6
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Stage 4
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Eight incompletely separated cells
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Segmentation (cleavage)
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16 cells, fourth cleavage
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Stage 7
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Stage 5
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2 completely closed blastomeres, 14 blastocones
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Segmentation (cleavage)
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32 cells, fifth cleavage
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Stage 8
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Stage 6
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12 blastomeres, 20 blastocones
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Segmentation (cleavage)
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64–66 cells, sixth cleavage
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Stage 9
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Stage 7
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36 blastomeres, 28 blastocones
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Segmentation (cleavage)
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Stage I
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Stage 10
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Stage 8
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Morula (advanced cleavage)
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Segmentation (cleavage)
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Stage II
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Stage 10
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Stage 9
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Blastula
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Segmentation (cleavage)
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Stage III
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Stage 11
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Stage 10
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Onset of epiboly
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Gastrulation
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Stage IV
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Stage 12
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Stage 11–12
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Formation of the germinal disk (yolk envelope & embryonic proper)
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Gastrulation
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Stage V
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Stage 13
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Stage 13
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Epiboly continues
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Gastrulation
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Stage VI
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Stage 14–15-16
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Stage 14
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Mesoderm concentrations become more distinct (smooth surface)
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Epiboly
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Stage VII.1
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Stage 17
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Stage 15
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Visible thickening of placodes starts
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Epiboly
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Stage VII.2
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Stage 18
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Stage 15
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Primordia of mantle, eyes, mouth and arms visible
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Epiboly/ Organogenesis
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Stage VIII
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Stage 19
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Stage 16
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Mouth and eye invagination, funnel pouches and statocysts visible
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Organogenesis
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Stage IX
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Stage 20
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Stage 17
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Primordia more prominent. Funnel tube rudiments are distinct
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Organogenesis
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Stage X
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Stage 21
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Stage 18
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Eye vesicles closed and sticking out. Funnel tube rudiments fuse ventrally
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Organogenesis
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Stage XI
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Stage 22
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Stage 19
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Mantle starts to grow. Funnel tube rudiments bend towards midline
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Organogenesis
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Stage XII.1
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Stage 23
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Stage 20
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Funnel tube rudiments start to form a tube ventrally. Mantle covers 1/2nd of gills
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Organogenesis
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Stage XII.2
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Stage 23
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Stage 20
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Funnel formed siphon at ventral extremity. Mantle bowl-shaped
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Organogenesis
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Stage XIII
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Stage 23
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Stage 21
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Formation of the funnel complete. Iris fold rudiment visible
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Organogenesis
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Stage XIV
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Stage 24
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Stage 22
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Mantle as wide as long and covers gills completely
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Organogenesis
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Stage XV.1
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Stage 25
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Stage 23
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Mantle covers ventral margin of funnel. Inner yolk strongly constricted
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Organogenesis
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Stage XV.2
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Stage 26
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Stage 24
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Mouth starts to internalize
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Organogenesis
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Stage XVI
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Stage 27
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Stage 25–26
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Few anterior chromatophores evident. Mouth completely covered by arm crown
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Organogenesis
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Stage XVII
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Stage 28
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Stage 27
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Mantle enlarged in relation to head. Chromatophores numerous
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Organogenesis
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Stage XVIII.1
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Stage 28
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Stage 27
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Yolk sac same size as head (Octopus & Loligo)
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Growth
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Stage XVIII.2
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Stage 28
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Stage 27
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Chromatophores darker
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Growth
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Stage XIX.1-XIX.2
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Stage 29
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Stage 28
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Pigmentation of ink sac. Eyes covered with iridophores
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Growth
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Stage XX.1
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Stage 29
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Stage 29
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Yolk nearly depleted
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Growth
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Stage XX.2
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Stage 30
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Stage 30
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Loss of outer yolk and hatchling
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Growth
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