Time | Ectoderm | Mesoderm | Endoderm | Traditional staging terminology |
---|---|---|---|---|
3–5 dpf | Circumoral ciliary band 2–4 serotonergic neurons in apical organ Apical tuft | Apical strand Pharyngeal circular muscles Protocoel, pore canal and hydropore | Tripartite gut | Müller stage Larva just recognizable as a tornaria, longitudinal ciliary bands formed, telotroch not yet present |
5–10 dpf | Eyespots Telotroch formation, neurotroch Neuropil, dorsal axons | Anchoring muscles |  | Heider stage Longitudinal ciliary bands without development of lobes and saddles; telotroch just formed. |
10–18 dpf | Dorsal cluster of 5HT neurons in apical organ Telotroch fully formed |  |  | |
18–22 dpf | Primary dorsal saddles and lobes Ventral saddle Addition of cell bodies in apical organ |  |  | Metschnikoff stage Primary lobes and saddles in formation or formed. Trunk coeloms not yet or having just appeared. |
22–30 dpf | Apical tuft disappears Primary ventral saddles and lobes Lower dorsal lobe | Longitudinal muscles in pharynx Mesocoels and metacoels |  | Krohn stage Secondary lobes and saddles or tentacles formed or forming. Trunk coelom usually present. Collar coelom not yet present or just first appearing. Large size. The high point of larval development. |
30–50 dpf | Secondary telotroch | Pulsatile vesicle |  | |
50–65 dpf | Serotonergic cell bodies throughout ectoderm Well-developed serotonergic nerve net | Apical strand disappears Mesocoels and metacoels increase in size Muscle fibers in coeloms | Gill slits (5 pairs) | Spengel stage Secondary lobes and saddles in regression or regressed. Collar and trunk coeloms present. Smaller than the previous stage, club shaped. Circular constriction about the middle of the body. Opaque. |
0–5 h post onset of metamorphosis | Thickening of epidermis Gill pore formation | Expansion of all coeloms (reduction of blastocoelar space) | Digestive tract retracts posteriorly | |
5–11 h post-onset of metamorphosis | Food grooves disappear Circumoral ciliary band disappears | Protocoel replaces blastocoelar space in proboscis Larval pharyngeal muscles disappear Trunk musculature develops | Pharynx posterior to the mouth | Agassiz stage Secondary lobes and saddles gone. Collar and trunk coeloms well developed. Regionalization indistinct. Entire body more elongate than in previous stage. Analfield a conical bulge. Longitudinal ciliary bands shifted toward the apical plate, the gut shifted analward. Protocoel very large. |
12–24 h post-onset of metamorphosis | Epidermis opaque Protocoel fills entire proboscis | Mesocoels replace blastocoelar space in collar Well-developed longitudinal muscles in trunk | Growth of pharynx Growth of gill slits Stomach folds | |
24–48 h post-onset of metamorphosis | Resorption of telotroch Transition from swimming to burrowing Eyespots disappear | Metacoels replace blastocoelar space in trunk | Additional gill slits | Metamorphosis stage Metamorphosis begins at the end of larval life. Proboscis, collar, and trunk regions delineated. Ciliary rows or tentacles in atrophy. Appearance of gill slits and buccal diverticulum. |
In all germ layers: clear division of body into proboscis, collar and trunk. Trunk growth |