Bottletail and bobtail squids, small marine invertebrates, are easy to collect and reproduce quickly. They can also be raised in large numbers in labs, making them valuable model animals for research. They are cephalopods, related to true squids, octopus and cuttlefish. Scientists still don't know much about them. Researchers have now published a study in Communications Biology that shows that bottletail squid (bobtail squid) and their common ancestor share some genetic similarities. This suggests that the major biogeographic events that led to the diversification of species might also have been involved."With 68 species recognized, bobtailsquid are a diverse family. They have been divided into three subfamilies. The study revealed that one subfamily is further divided into two geographical lineages. Dr. Gustavo Sanchez (researcher at Hiroshima University and former Visiting Student in Okinawa Institute of Science and Technology Graduate University’s (OIST), Molecular Genetics Unit) was one of the leading authors. "In 2019, we discovered a new species bobtail squid as part of my research at OIST. This highlights both the diversity and the unknowns."Sepiolida is made up of bobtail and bottletail Squids. They are small and can live for between 1-8 cm.Dr. Sanchez and researchers from OIST, Galway and the National University of Ireland collected 32 species of bobtail squids across the Indo-Pacific and Mediterranean Seas for this new study. Genome skimming is a method that sequences entire genomes at low coverage. They were able to examine the genetic differences between these species and thus estimate their evolutionary relationships.The results showed that the bobtail and bottletail Squids split up into separate families about 66 million years ago. This is consistent with modern marine fishes' rapid diversification after the disappearance of other ancient groups (the same one that decimated most dinosaurs). The Bobtail squid continued to diversify into three subfamilies, Sepiolinae, Rossinae, as well as Heteroteuthinae. Sepiolinae is the largest subfamily. It can be further divided into two tribes, those found in the Indo-Pacific Ocean, the Mediterranean Sea, and the Atlantic Ocean. This split occurred around 50 million years ago with another important biogeographic event, the closing of the Tethys sea. This caused the separation of the two regions and led to the division of this subfamily in two.The second part of the study was focused on the evolution and production of luminescence in bobtailsquid. Many of these animals need luminescence to survive. It allows them to avoid predators at night and counter-illumination. Researchers discovered that the Sepiolinae subfamily's ancestor likely had a bilobed-lit organ that contained luminescence-producing bacteria. It has been preserved by many species today, but it was lost in two groups: one in the Indo Pacific tribe and one in the Mediterranean-Atlantic tribal.Professor Daniel Rokhsar who heads the OIST Unit said that although it is still necessary to investigate the evolutionary relationship of almost 50% of bobtailsquids, this research has provided a solid foundation for classifying bobtails and bottletailsquids. We hope this phylogenetic and ancestral reconstructions will prove useful in future research.