The coelacanth braincase is 98.5% filled with fat; only 1.5% of the braincase contains brain tissue. The cheeks of the coelacanth are unique because the opercular bone is very small and holds a large soft-tissue opercular flap. A spiracular chamber is present, but the spiracle is closed and never opens during development. Coelacanth also possess a unique rostral organ within the ethmoid region of the braincase. Also unique to extant coelacanths is the presence of a "fatty lung" or a fat-filled single-lobed vestigial lung, homologous to other fishes' swim bladder. The parallel development of a fatty organ for buoyancy control suggest a unique specialization for deep-water habitats. There are small, hard but flexible plates around the vestigial lung in adult specimen, though not around the fatty organ. The plates most likely had a regulation function for the volume of the lung. Due to the size of the fatty organ, researchers assume that it is responsible for the kidney's unusual relocation. The two kidneys, which are fused into one, are located ventrally within the abdominal cavity, posterior to the cloaca. In 2013, a group led by Chris Amemiya and Neil Shubin published the genome sequence of the coelacanth in the journal "Nature". The African coelacanth genome was sequenced and assembled using DNA from a Comoros Islands "Latimeria chalumnae" specimen. It was sequenced by Illumina sequencing technology and assembled using the short read genome assembler ALLPATHS-LG. Due to their lobed fins and other features, it was once hypothesized that the coelacanth might be the most recent shared ancestor between terrestrial and marine vertebrates. But after sequencing the full genome of the coelacanth, it was discovered that the lungfish is the most recent shared ancestor. Coelacanths and lungfish had already diverged from a common ancestor before the lungfish made the transition to land. Another important discovery made from the genome sequencing is that the coelacanths are still evolving today (but at a relatively slow rate). One reason the coelacanths are evolving so slowly is the lack of evolutionary pressure on these organisms. They have few predators, and live deep in the ocean where conditions are very stable. Without much pressure for these organisms to adapt to survive, the rate at which they have evolved is much slower compared to other organisms.