Genome Announcement: Further Improved Genome Assembly of .

Nematodes such as and are powerful models for associating phenotypes to genotypes. However, exploring the evolution of identified genetic loci requires a robust phylogenomic framework. Here, we present an updated genome of the nematode which is the only known member of the sister group of . Reassembly of previously generated long read sequencing data combined with new Hi-C data resulted in a near chromosome-scale genome assembly spanning 302.5Mb. The Hi-C contact map, karyotyping data and comparative genomic analysis support an organization of the genome into six chromosomes, whereby all autosomes correspond to individual Nigon elements and the sex chromosome represents a fusion of Nigon elements D and X. The further improved genome will be useful as an outgroup for dating and polarizing lineage-specific genomic signatures.