Stage 33
This corresponds to the Late Tail Absorption Stage (CirobuD:0000056; 29-30 h), during which the tail becomes completely absorbed. Together with the tail, the 88 larval entities associated with the embryonic and larval stages are no longer recognizable.
Both the notochord and the tail muscles are folded several times and coiled into the posterior trunk. Moreover, the posterior trunk epidermis wraps around the absorbing tail. Strong actin staining can still be observed in the absorbing axial organ (muscles and notochord) and in the degenerating tail epidermis.
In histological sections, several newly formed structures associated with the juvenile lifestyle can be defined. Some of them are the body wall (CirobuA:0000857), the atrial siphon muscles (CirobuA:0000367), and the pericardial cavity (CirobuA:0000678) (Hirano and Nishida, 1997; Stolfi et al., 2014, 2010; Wang et al., 2013). The stalk continues to elongate. Tunic cells are numerous in the definitive tunic (the original inner compartment of the tunic with its inner cuticular layer).