A lophotrochozoan twist gene is expressed in the ectomesoderm
of the gastropod mollusk Patella vulgata.
The first three quartets give rise to ectodermal tissues, including the two ocelli (derived from la and lc micromeres), as well as ectomesoderm
(from 2c, 3a, and 3b micromeres).
lacteus is derived as ectomesoderm
from the 3a and 3b micromeres, and as endomesoderm from the 4d micromere.
Other changes have occurred in the sub-lineages that give rise to certain structures, such as the ciliated band (derived from first, second, and third quartet derivatives) and the ectomesoderm
(derived entirely from 3a and 3b).