The initial swimming gastrula, or protrochophore, is completely ciliated but lacks any trochal band.
Ciliary structures: apical tuft present; one pair of lateral bristles form; trochal band absent
A distinct trochal band is not present at this stage.
A distinct trochal band is first visible at the level of the intestine, here referred to as a mesotroch, following the terminology of Okada (1957).
The first is the appearance of a second trochal band just anterior to the existing mesotroch.
A particularly distinctive cell type is that of the ciliated cells of the trochal bands.
Four other differences are apparent between our results and those in figure 5 of Cazaux (1965): (i) we do not detect trochal bands around the stomodeum; (ii) a distinct intestine is visible, rather than the extension of the posterior stomach shown; (iii) the mesotroch is more posterior in our preparations; (iv) only one pair of laterally placed eyes are visible rather than the two pairs depicted.
At Stage L4 another trochal band, which we also call a mesotroch, forms just anterior to the first band.