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. 2020 Oct 21;10:17916. doi: 10.1038/s41598-020-73544-9

Table 1.

Ciona developmental stages from the Larva Period to the Juvenile Period. Stages 1–41 were defined in the paper, Stages 1–37 described.

Stage Stage name Characteristics Time after fertilization 18 ℃ (hour post fertilization) Time after hatch 20 ℃1 (hour post hatch) ANISEED 2017

Embryonic development, pre-metamorphosis

CirobuD:0000003

VI. Larva Period (St. 26–29, 17.5–24hpf)2

St. 26

CirobuD:0000049

 Hatching larva Hatching, spherical trunk shape, immature papillae with pyramidal shape, irregular tail movements 17 h 30 min (17.5 hpf) 0 St. 26

St. 27

CirobuD:0000050

 Early swimming larva Spindle-like trunk shape, regular tail movements and swimming behaviour 17.5–20 hpf – St. 27

St. 28

CirobuD:0000051

 Mid swimming larva Elongated papillae and expansion of their basal part, squared trunk, spherical test cells, cilia in epidermal sensory neurons recognizable, preoral lobe recognizable 20–22 hpf – St. 28

St. 29

CirobuD:0000052

 Late swimming larva Longer and narrower head with respect to St. 28, trunk profile squared at transition between trunk and tail 22–24 hpf – St. 29, 30

Metamorphosis

CirobuD:0000004

VII. Adhesion period (St. 30–31, 24–27 hpf)

St. 30

CirobuD:0000053

 adhesion Curved papillae, otolith and ocellus remnants recognizable 24–27 hpf 6.5–9.5hph St. 31, 32
VIII. Tail absorption period (St. 32–34, 27–30 hpf)

St. 31

CirobuD:0000054

 Early tail absorption Beginning of tail absorption, tail bending at the transition between trunk and tail, otolith and ocellus remnants recognizable 27 hpf Avg. 9.9 hph St. 33

St. 32

CirobuD:0000055

 Mid tail absorption 50% of tail absorbed into trunk; tail shrinked and thickened, otolith and ocellus remnants recognizable 28 hpf Avg. 10.4 hph St. 34

St. 33

CirobuD:0000056

 Late tail absorption Tail completely resorbed, papiliae no more recognizable, otolith and ocellus remnants recognizable 29 hpf Avg. 11.4 hph St. 35
IX. Body axis rotation period (St. 35–37, 30–60 hpf)

St. 34

CirobuD:0000057

 Early body axis rotation Beginning of body axis rotation (angle between the stalk and the endostyle more than 0°), outer tunic compartment and outer cuticle layer no more present, tunic cells recognizable in definitive tunic, otolith and ocellus remnants recognizable 30–36 hpf Avg. 17.7 hph St. 36

St. 35

CirobuD:0000058

 Mid body axis rotation Body axis rotation of about 30°–60°, one pair of gill-slit recognizable, otolith and ocellus remnants recognizable 36–45 hpf Avg. 27 hph St. 37, 38

St. 36

CirobuD:0000059

 Late body axis rotation Two pairs of gill-slit open, body axis rotation of about 80°–90°, filtering and feeding activity present, otolith and ocellus remnants recognizable, heart beating 45–60 hpf Avg. 37.5 hph St. 39, 40
Post-metamorphosisCirobuD:0000005
X. Juvenile period (St. 37–41, 60 hpf–)

St. 37

CirobuD:0000060

 Early juvenile I Body axis rotation completed, stomach swollen, otolith and ocellus remnants recognizable 63–72 hpf (3 dpf) 45.5–54.5 hph St. 41, 42

St. 38

CirobuD:0000061

 Early juvenile II Larval tail remnants totally adsorbed 3–4 dpf 3 dph St. 43, 44

St. 39

CirobuD:0000062

 Mid juvenile I Additional gill slit begin to open, appearance of stomach, gut and neural grand 4–6 dpf 5 dph St. 45

St.40

CirobuD:0000063

 Mid juvenile II Gonad in form of oval vesicle (corresponding to Stage 6 in Chiba et. al., 2004) 6–7 dpf 6 dph St. 46

St.41

CirobuD:0000064

 Late juvenile Atrial siphon begins to fuse (corresponding to Stage 7 in Chiba et. al., 2004) 7 dpf– 6 dph– St. 47

1The average time course of Tail absorption period and Body axis rotation period in same batch was set-up once again after hatching.

2The duration of larval swimming differs among individuals. Matsunobu et al. (2015) showed that the hatched larva requires at least three or four hours to get competence to commence metamorphosis. So the time after fertilization during Larva Period was broad.