Extended Data Fig. 1: The genome of Owenia fusiformis is conservatively evolving.

a, Differential interface contrast (DIC) images and z-stack confocal laser scanning views of a C. teleta trochophore larva stained for DAPI and acetylated α-tubulin. b,c, Pie charts of the transposable element content and Kimura substitution plots of transposable element divergence for O. fusiformis and other selected annelid species belonging to different annelid clades as depicted in c. Unlike H. robusta and L. luymesi, which show bursts of transposable elements, O. fusiformis shows more steady rates of expansion. d, Gene family evolution analysis across 22 metazoan lineages under a consensus tree topology. Gains are shown in green, losses in violet. Gene family losses in O. fusiformis are like those of slow-evolving lineages. e, Principal component analysis from Fig. 1b, showing the full set of species. f,g, O. fusiformis has the lowest number of gene losses of all sampled annelids (e), and the least gene expansions (f) after the extremely compact genome of D. gyrociliatus. h, Macrosynteny analysis between O. fusiformis, and from top to bottom, the cephalochordate Branchiostoma floridae, the bivalve Pecten maximus, and the annelid Streblospio benedicti. Owenia fusiformis retains ancestral linkage groups but also exhibits annelid- and species-specific chromosomal arrangements. However, the karyotype of O. fusiformis is more conserved than that of the annelid S. benedicti. i, Macrosynteny analysis between the bivalve P. maximus and the nemertean worm L. longissimus. Lineus longissimus exhibits conserved ancestral bilaterian linkage groups, including three potential lophotrochozoan-specific chromosomal rearrangements (H+Q, J2+L and K+O2), plus a nemertean-specific fusion (G+C1). Scale bar in a, 50 µm.