With the help of a new draft genome sequence, a Japanese research team explores the evolutionary history of the Argonauta argo, commonly known as the greater argonaut or paper nautilus. The octopus, which is adapted to open ocean "pelagic" zones, is known for producing a shell-like case to protect its eggs. As they report in Genome Biology and Evolution, the researchers put together a 1.1 gigabase draft genome for the cephalopod that contains more than 26,400 predicted protein-coding genes — a genome that is modest in size relative to those of other cephalopods. Through gene cluster, pathway, and comparative genomic analyses, the authors delved into the sequence data to search for explanations for the egg case, among other characteristic features, uncovering egg case evolution distinct from the genes used to produce shells in ancestral species. "We found that this species has an exceptionally small genome size, making it an ideal species for genomic studies," they note, adding that the study "allowed us to gain insights into the genomic basis of adaptation to the open ocean holopelagic lifestyle of this species in particular, and the evolution of cephalopods in general."