 The study reports chromosome-level genome assemblies of two related CNM&s, revealing a robust set of 15 chromosomes with clear one-to-one correspondence between the species. The genomes show chromosomal conservation, allowing for reconstruction of ancestral chlidarion and metazoan chromosomal blocks. The Hox and MK clusters are largely disintegrated in contrast to bilateria, suggesting fundamental differences in long-range gene regulation compared to vertebrates. This article was offered by Bob Zimmerman, Juan de Monti Negro, Sophia M. C. Robb, and others.