CIRCOS plots for 4 new chitons genome assemblies, clockwise from top left: one species in the order Lepidopleurida Deshayesiella sirenkoi, and three species in the clade Chitonida sensu lato: Acanthochiton rubrolineata, A. discrepans, and Callochiton septemvalvis. Each quarter circle shows the pseudochromosome content for each species, in order of size, with concentric rings indicating GC content, gene count, percent repeat content, and a photograph of the respective species.

Phylogeny of Mollusca, with new genomes noted in bold type, and the chromosome number in square brackets for each species where known. Lineages with known whole (double circle) or partial genome (single circle) duplication are in thicker lines for emphasis; boxes on branches show the reconstructed ancestral 1n chromosome number for the respective clade.

Evolution of the ancestral molluscan linkage groups (MLGs) within Polyplacophoran using the lineage leading to Acanthochitona discrepans as an example. MLGs are distinguished by colours, at the top of the diagram and in the key at bottom showing the number of orthologs. Each row is the reconstructed karyotype of the ancestor of living Polyplacophora, the order Chitonida sensu lato, and the genus Acanthochitona.

Syntenic rearrangements of MLGs within the evolution of Polyplacophora. Each part shows the reconstructed karyotypes of an ancestor (middle) and two descendent lineages, with a schematic cladogram for orientation. From left to right, the divergence of A) ancestor of Polyplacophora, leading to the lepidopleuran species Deshayesiella sirenkoi (left) and ancestor of Chitonida (right), B), ancestor of Chitonida leading to the callochitonid Callochitona septemvalvis (left) and chitonid Liolophura japonica (right) and C) ancestor of the genus Acanthochitona leading to the two congeneric species A. rubrolineata (left) and A. discreapans (right). Colours and presentation are as in Figure 3. Chromosome fusions are highlighted with chromosome numbers in black boxes, and duplications in white boxes.

Oxford plots comparing gene occupancy of species from four different classes of molluscs (vertical) to the ancestral molluscan linkage groups (MLG, horizontal): A) the bivalve Archivesica marisinica retains a plesiomorphic karyotype reflecting the 20 MLGs, B) the chiton Liolophura japonica has large scale gene duplication in MLG11 and MLG17 on separate pseudochromosomes, C) the scaphopod Siphonodetalium dalli has large scale gene duplication of MLG13 and MLG03 on separate pseudochromosomes, D) the gastropod Rapana venosa demonstrates a nearly whole genome duplication with MLG20 not duplicated. Colours follow the presentation in Figure 3.