I obtained a genome from NCBI. For instance, Haloquadratum walsbyi strain AM180088.1. But the FASTA file contain two parts. The first part marked as >AM180088.1 Haloquadratum walsbyi DSM 16790 complete genome The second part marked as >AM180089.1 Haloquadratum walsbyi DSM 16790 plasmid PL47 complete genome What does that mean? In particular, the second one "plasmid"? If it is called complete genome should it all in one? Why divide into parts?