Rhizocephalans seem more like fungi than animals. Only their developmental stages mark them out as animals, crustaceans and barnacles. Sacculina carcini that Deutsch's team turned in their quest to find the elusive back end of the barnacle, as they explain in Evolution and Development 1 . Their epic journey was aided immeasurably by the high-tech tools of genomics. The researchers traced, in this species, two copies of a gene called engrailed .
Sacculina larvae are just the same.
Engrailed is expressed in bold stripes marking the head and thorax.