Here we show first that the Sacculina caudal gene is expressed early in embryogenesis, which makes it the earliest genetic marker evidenced in the development of Sacculina and of any other crustacean species. It is expressed later in the embryo in the caudal papilla, a posterior proliferating zone of cells. Surprisingly, it is never expressed in the vestigial abdomen. This lack of expression of the Sacculina caudal gene in a posterior region, at odds with what is known in all other studied metazoan species, might be correlated with the defective development of the abdomen. Several of these show related patterns of expression within a wide variety of animals belonging to different phyla.
Crustaceans show a wide variety of body plans.
We addressed the question of the genetic mechanism underlying this peculiar feature. We took this as evidence for the determination of a vestigial abdomen. It was worth looking for other developmental genes putatively involved in abdomen formation. We report here the cloning, sequencing, and expression pattern of a partial cDNA of the caudal gene of Sacculina carcini . It is the earliest genetic marker ever reported in crustacean development.