Table 2 Comparative developmental guide for cephalopod development

Fertilized egg

Stage 1

Stage 1

Newly laid fertilized egg that did not finish maturation

Segmentation (cleavage)

First maturation division

Stage 2

Stage 1

First polar body

Segmentation (cleavage)

Second maturation division

Stage 3

Stage 1

3 polar bodies

Segmentation (cleavage)

2 cells, first cleavage

Stage 4

Stage 2

Two partially separated cells

Segmentation (cleavage)

4 cells, second cleavage

Stage 5

Stage 3

Four partially separated cells

Segmentation (cleavage)

8 cells, third cleavage

Stage 6

Stage 4

Eight incompletely separated cells

Segmentation (cleavage)

16 cells, fourth cleavage

Stage 7

Stage 5

2 completely closed blastomeres, 14 blastocones

Segmentation (cleavage)

32 cells, fifth cleavage

Stage 8

Stage 6

12 blastomeres, 20 blastocones

Segmentation (cleavage)

64–66 cells, sixth cleavage

Stage 9

Stage 7

36 blastomeres, 28 blastocones

Segmentation (cleavage)

Stage I

Stage 10

Stage 8

Morula (advanced cleavage)

Segmentation (cleavage)

Stage II

Stage 10

Stage 9

Blastula

Segmentation (cleavage)

Stage III

Stage 11

Stage 10

Onset of epiboly

Gastrulation

Stage IV

Stage 12

Stage 11–12

Formation of the germinal disk (yolk envelope & embryonic proper)

Gastrulation

Stage V

Stage 13

Stage 13

Epiboly continues

Gastrulation

Stage VI

Stage 14–15-16

Stage 14

Mesoderm concentrations become more distinct (smooth surface)

Epiboly

Stage VII.1

Stage 17

Stage 15

Visible thickening of placodes starts

Epiboly

Stage VII.2

Stage 18

Stage 15

Primordia of mantle, eyes, mouth and arms visible

Epiboly/ Organogenesis

Stage VIII

Stage 19

Stage 16

Mouth and eye invagination, funnel pouches and statocysts visible

Organogenesis

Stage IX

Stage 20

Stage 17

Primordia more prominent. Funnel tube rudiments are distinct

Organogenesis

Stage X

Stage 21

Stage 18

Eye vesicles closed and sticking out. Funnel tube rudiments fuse ventrally

Organogenesis

Stage XI

Stage 22

Stage 19

Mantle starts to grow. Funnel tube rudiments bend towards midline

Organogenesis

Stage XII.1

Stage 23

Stage 20

Funnel tube rudiments start to form a tube ventrally. Mantle covers 1/2nd of gills

Organogenesis

Stage XII.2

Stage 23

Stage 20

Funnel formed siphon at ventral extremity. Mantle bowl-shaped

Organogenesis

Stage XIII

Stage 23

Stage 21

Formation of the funnel complete. Iris fold rudiment visible

Organogenesis

Stage XIV

Stage 24

Stage 22

Mantle as wide as long and covers gills completely

Organogenesis

Stage XV.1

Stage 25

Stage 23

Mantle covers ventral margin of funnel. Inner yolk strongly constricted

Organogenesis

Stage XV.2

Stage 26

Stage 24

Mouth starts to internalize

Organogenesis

Stage XVI

Stage 27

Stage 25–26

Few anterior chromatophores evident. Mouth completely covered by arm crown

Organogenesis

Stage XVII

Stage 28

Stage 27

Mantle enlarged in relation to head. Chromatophores numerous

Organogenesis

Stage XVIII.1

Stage 28

Stage 27

Yolk sac same size as head (Octopus & Loligo)

Growth

Stage XVIII.2

Stage 28

Stage 27

Chromatophores darker

Growth

Stage XIX.1-XIX.2

Stage 29

Stage 28

Pigmentation of ink sac. Eyes covered with iridophores

Growth

Stage XX.1

Stage 29

Stage 29

Yolk nearly depleted

Growth

Stage XX.2

Stage 30

Stage 30

Loss of outer yolk and hatchling

Growth